Fearful thoughts take many different forms. Sometimes they sound reasonable: “I’m just being careful, so I’m taking my time.” Other times they are tied to your past: “I’ve tried that before and it didn’t work.” Occasionally, fears are cleverly disguised as being realistic: “Most people fail, so I want to be absolutely sure before I get started.” I could fill page after page with other examples. Yet when you take a close, honest look at every fearful thought, there are threads of similarity. All of them are explanations or rationalizations for why something shouldn’t or can’t work. They are usually justifications for quitting, or for not getting started.

Fearful thoughts hold you back, not some but all of the time.

A critic, especially a fearful one, will look at this advice and say it’s unrealistic, simplistic, and/or foolish. The problem with overcoming these objections is that, on the surface, they sound reasonable. Let me assure you that I’m not suggesting you ignore the facts and take unnecessary and/or foolish risks.

What I’m talking about here are the fears that clearly and directly interfere with your dreams – the fear of rejection, the fear of failure; thoughts like “What will everyone think of me? I might look foolish,” or “I don’t think I can do it, I don’t have the time, or the experience, or the confidence.” These common, ongoing fearful thoughts are the dream snatchers of our own making.

I encountered a beautiful problem last time, hence writing this post to help those who have the same problem.

Problem: My task is to download files from the servers as a zip file format through Java Code. I created one zip file and added all files to that zip. Finally write that zip file in servlet out put stream. But interesting thing is this works perfectly in Firefox/Mozila but failed in IE6/7,

Following is the code snippet for this:

String zipfilePath = (new StringBuilder(String.valueOf(getServlet().getServletContext().getRealPath(“/”)))).append(“upload”).append(“//”).append(“Allattachements.zip”).toString();

ZipOutputStream out = null;
out = new ZipOutputStream(new FileOutputStream(zipfilePath));

//Code to add all files to zip goes here

//Start download code

File                f        = new File(zipfilePath);
int                 length   = 0;
ServletOutputStream op       = resp.getOutputStream();

resp.setContentLength( (int)f.length() );
resp.setHeader( “Content-Disposition”, “attachment; filename=\”" +  some_filename + “\”" );
resp.setContentType( (mimetype != null) ? mimetype : “application/octet-stream” );

byte[] bbuf = new byte[18024];
DataInputStream in = new DataInputStream(new FileInputStream(f));

while ((in != null) && ((length = in.read(bbuf)) != -1))
{
op.write(bbuf,0,length);
}

in.close();
op.flush();
op.close();
}

In IE what happen when we click on the download option is just cant imagine.

I am prompted for download option, but after downloading the file, i found another file inside the downloadzip with same name as of the downloadzip file , but with no extension, when i 7zip the file, all other files are there in side it.

I started some experiment, finally able to download the correct format.

Here is the solution:

Every thing will remain same just changed the content type:

resp.setContentLength( (int)f.length() );
resp.setHeader( “Content-Disposition”, “attachment; filename=\”" +  original_filename + “\”" );
resp.setContentType(“application/octet-stream” );
resp.setHeader (“Pragma”, “public”);
resp.setHeader(“Cache-control”, “must-revalidate”);

You need to set the Pragma to public. SO it will works for Ie. as well as set the  contentType to “application/octet-stream”

Thanks

http://www.developersbook.com/

PDF Search Engine

http://www.pdf-search-engine.com/

Spring Framework Best Practice

http://lijinjoseji.wordpress.com/2007/09/27/spring-framework-best-programming-practices/

Struts, Spring, Hibernate Tutorial

===============================

http://www.vaannila.com

Employee.java

package jyoti;
import java.util.Date;
public class Emp {

private int empno;
private String ename;
private String job;
private int mgr;
private Date hiredate;
private float sal;
private float comm;
//private int deptno;
private Dept dept;

public Emp() {
super();
// TODO Auto-generated constructor stub
}

public Emp(int empno, String ename, String job, int mgr, Date hiredate, float sal, float comm, Dept dept) {
super();
this.empno = empno;
this.ename = ename;
this.job = job;
this.mgr = mgr;
this.hiredate = hiredate;
this.sal = sal;
this.comm = comm;
this.dept = dept;
}

public Emp(String ename, String job, float sal) {
super();
this.ename = ename;
this.job = job;
this.sal = sal;
}

public int getEmpno() {
return empno;
}
public void setEmpno(int empno) {
this.empno = empno;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
public int getMgr() {
return mgr;
}
public void setMgr(int mgr) {
this.mgr = mgr;
}
public Date getHiredate() {
return hiredate;
}
public void setHiredate(Date hiredate) {
this.hiredate = hiredate;
}
public float getSal() {
return sal;
}
public void setSal(float sal) {
this.sal = sal;
}
public float getComm() {
return comm;
}
public void setComm(float comm) {
this.comm = comm;
}

public Dept getDept() {
return dept;
}
public void setDept(Dept dept) {
this.dept = dept;
}

}

employee.hbm.xml

<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE hibernate-mapping PUBLIC
“-//Hibernate/Hibernate Mapping DTD 3.0//EN”
“http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd”>
<hibernate-mapping>
<class name=”jyoti.Emp” table=”emp” lazy=”true”>
<id name=”empno” type=”int” column=”empno” >
<generator/>
</id>
<property name=”ename”>
<column name=”ename” />
</property>
<property name=”job”>
<column name=”job”/>
</property>
<property name=”mgr” not-null=”false”>
<column name=”mgr”/>
</property>
<property name=”hiredate”>
<column name=”hiredate” />
</property>
<property name=”sal”>
<column name=”sal”/>
</property>
<property name=”comm”>
<column name=”comm”/>
</property>

<many-to-one name=”dept” column=”deptno” not-null=”false”>
</many-to-one>
</class>
</hibernate-mapping>

Dept.java

package jyoti;

import java.util.Set;

public class Dept {

private int deptno;
private String dname;
private String loc;
private Set employee;

public Dept() {
super();
// TODO Auto-generated constructor stub
}
public int getDeptno() {
return deptno;
}
public void setDeptno(int deptno) {
this.deptno = deptno;
}
public String getDname() {
return dname;
}
public void setDname(String dname) {
this.dname = dname;
}
public String getLoc() {
return loc;
}
public void setLoc(String loc) {
this.loc = loc;
}
public Set getEmployee() {
return employee;
}
public void setEmployee(Set employee) {
this.employee = employee;
}
}

dept.hbm.xml

<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE hibernate-mapping PUBLIC
“-//Hibernate/Hibernate Mapping DTD 3.0//EN”
“http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd”>
<hibernate-mapping>
<class name=”jyoti.Dept” table=”dept” lazy=”true”>
<id name=”deptno” type=”int” column=”deptno” >
<generator/>
</id>
<property name=”dname”>
<column name=”dname” />
</property>
<property name=”loc”>
<column name=”loc”/>
</property>
<set name=”employee” inverse=”true” cascade=”all” lazy=”true” batch-size=”9″>
<key>
<column name=”deptno”/>
</key>
<one-to-many class=”jyoti.Emp”/>
</set>
</class>
</hibernate-mapping>

TestClass.java

public class FirstExample {
public static void main(String[] args) {
Session session = null;

try{

SessionFactory sessionFactory = new Configuration().configure(“/hibernate.cfg.xml”).buildSessionFactory();
session =sessionFactory.openSession();
session.setFlushMode(FlushMode.AUTO);
org.hibernate.Transaction tx = session.beginTransaction();
Set ofemp = new HashSet();
System.out.println(“Inserting Record”);
Emp emp = new Emp();
//emp.setEmpno(19);

emp.setEname(“Jyoti”);
emp.setJob(“Analyst”);
emp.setMgr(4578);
Date d= new Date();
emp.setHiredate(d);
ofemp.add(emp);
Emp emp1 = new Emp();
//emp.setEmpno(19);

emp1.setEname(“Jyoti”);
emp1.setJob(“Analyst”);
emp1.setMgr(4578);
Date d2= new Date();
emp1.setHiredate(d2);
ofemp.add(emp1);
//emp.setDept(10);
Dept dept = new Dept();
//ob.setDeptno(50);
dept.setDname(“CTC”);
dept.setLoc(“BBSR”);
dept.setEmployee(ofemp);
//session.save(emp); /*If cascade attribute is set to “true” then no need of this code. Hibernate trys to persist all at a time*/
//session.save(emp1); /*if inverse=”true” set then hibernate knows that there is a bidirectional association exist*/
session.save(dept);
tx.commit();
System.out.println(“Done”);

}catch(Exception e){
e.printStackTrace();
System.out.println(“sorry jyoti “+e.getMessage());
}finally{

try{
session.flush();
session.close();
}catch(Exception ee){
ee.printStackTrace();
System.out.println(“jyoti”);}

}

}
}

FOR INHERITANCE MAPPING IN HIBERNATE SEE THE FOLLOWING LINK

====================================================http://simsonlive.wordpress.com/2008/03/09/how-inheritance-works-in-hibernate/

A.1.

Making a class immutable

Immutability must be familiar to every one when we talk about String & StringBuffer classes in java. Strings are considered immutable because the values contained in the reference variable cannot be changed. Whereas String Buffer is considered mutable because the value in a string buffer can be changed (i.e. mutable).

However I always thought how to make our user defined classes as immutable though I am unaware as to why any one would need this.

The reason perhaps might be clear once we have a look at the code.

Now in order to make a class immutable we must restrict changing the state of the class object by any means. This in turn means avoiding an assignment to a variable. We can achieve this through a final modifier. To further restrict the access we can use a private access modifier. Above do not provide any method where we modify the instance variables.

Still done? No. How if some body creates a sub class from our up till now immutable class? Yes here lies the problem. The new subclass can contain methods, which over ride our base class (immutable class) methods. Here he can change the variable values.

Hence make the methods in the class also final. Or a better approach. Make the immutable class itself final. Hence cannot make any sub classes, so no question of over ridding.

The following code gives a way to make the class immutable.

/*
Code Developed By Ashish Agarwal
This code demonstrates the way to make a class immutable
*/

// The immutable class which is made final
final class MyImmutableClass
{
// instance var are made private & final to restrict the access

private final int count;
private final double value;

// Constructor where we can provide the constant value
public MyImmutableClass(int paramCount,double paramValue)
{
count = paramCount;
value = paramValue;
}

// provide only methods which return the instance var
// & not change the values

public int getCount()
{
return count;
}

public double getValue()
{
return value;
}
}

// class TestImmutable
public class TestImmutable
{
public static void main(String[] args)
{
MyImmutableClass obj1 = new MyImmutableClass(3,5);

System.out.println(obj1.getCount());
System.out.println(obj1.getValue());

// there is no way to change the values of count & value-
// no method to call besides getXX, no subclassing, no public access to var -> Immutable
}
}

The possible use of immutable classes would be a class containing a price list represented for a set of products.
Otherwise also this represents a good design.

2.Q What is a Marker Interface ?

Ans:

A marker interface is such an interface, by implementing which , your class object will get some special behavior.

Example: By implementing java.io.Serializable your class Object becomes Serializable.

By implementing java.lang.Runnable your Class becomes thread Class.

By implementing java.lang.Cloneable your Class Object can be cloned.

Q. 3: What is an invoker Servlet?

A:

Invoker Servlet

The Invoker servlet (or InvokerServlet) is a special servlet provided with Tomcat, which allows servlets to be called by simply using a /servlet URL, without having to configure each servlet individually in web.xml. It is disabled by default in new Tomcat installations and new Metawerx hosting accounts.

For example:

http://www.examplecompany.com/servlet/MyServlet

Why does it exist?

In older servlet containers, before web.xml was added to the specification, this was the default behaviour, so the Invoker Servlet was provided to avoid creating complex web.xml files.

Why is it disabled by default?

• The /servlet/ URL extension allows any class in your classpath to be accessed, as long as the class is a valid servlet. This is a security risk. Using web.xml configuration, the deployer of the application can define specifically which URL’s can be used.
• Secondly, the /servlet/ approach forces the use of java class names in the URL. Using web.xml configuration provides a way to define the URL instead, separating the class names from what the end-user sees in their browser’s URL bar.

Enabling the Invoker

• The Invoker is disabled by default, so it is necessary to change either the server-wide web.xml file, or add a small section to your applications web.xml (preferred method). To see how to do this, see Enabling the Invoker Servlet.

Usage tips

• The servlet name in the URL is the same as the servlet class name.
• The servlet should not be included in a package if you are planning on using it with the Invoker.

Q.4: Is Jsp by default thread safe ?

A: Short answer, no, JSPs by default are not automatically thread safe.

To make jsp as threadsafe we hav to make isThreadSafe=false
,so it sends only one request for processing.it implicitly
implement SingleThreadModel interface.

Just add the directive <%@ page isThreadSafe=”false” %> with the jsp page.

Q. 5: How to get a read only collection ?

  ArrayList list = new ArrayList();
  list.add(“first”);
  ...
  List readOnlyList = Collections.unmodifiableList(list);

public class DemoStringCreation {

  public static void main (String args[]) {
    String str1 = "Hello";
    String str2 = "Hello";
    System.out.println("str1 and str2 are created by using string literal.");
    System.out.println("    str1 == str2 is " + (str1 == str2));
    System.out.println("    str1.equals(str2) is " + str1.equals(str2));  

    String str3 = new String("Hello");
    String str4 = new String("Hello");
    System.out.println("str3 and str4 are created by using new operator.");
    System.out.println("    str3 == str4 is " + (str3 == str4));
    System.out.println("    str3.equals(str4) is " + str3.equals(str4));  

    String str5 = "Hel"+ "lo";
    String str6 = "He" + "llo";
    System.out.println("str5 and str6 are created by using string
constant expression.");
    System.out.println("    str5 == str6 is " + (str5 == str6));
    System.out.println("    str5.equals(str6) is " + str5.equals(str6));

    String s = "lo";
    String str7 = "Hel"+ s;
    String str8 = "He" + "llo";
    System.out.println("str7 is computed at runtime.");
    System.out.println("str8 is created by using string constant
expression.");
    System.out.println("    str7 == str8 is " + (str7 == str8));
    System.out.println("    str7.equals(str8) is " + str7.equals(str8));

  }
}

str1 and str2 are created by using string literal.
    str1 == str2 is true
    str1.equals(str2) is true
str3 and str4 are created by using new operator.
    str3 == str4 is false
    str3.equals(str4) is true
str5 and str6 are created by using string constant expression.
    str5 == str6 is true
    str5.equals(str6) is true
str7 is computed at runtime.
str8 is created by using string constant expression.
    str7 == str8 is false
    str7.equals(str8) is true

public class Program
{
    public static void main(String[] args)
    {
       String str1 = "Hello";
       String str2 = "Hello";
       System.out.print(str1 == str2);
    }
}

true

String a=new String("Hello");

public class Program
{
    public static void main(String[] args)
    {
       String str1 = "Hello";
       String str2 = new String("Hello");
       System.out.print(str1 == str2 + " ");
       System.out.print(str1.equals(str2));
    }
}

false true

public class Program
{
    public static void main(String[] args)
    {
        // Create three strings in three different ways.
        String s1 = "Hello";
        String s2 = new StringBuffer("He").append("llo").toString();
        String s3 = s2.intern();

        // Determine which strings are equivalent using the ==
        // operator
        System.out.println("s1 == s2? " + (s1 == s2));
        System.out.println("s1 == s3? " + (s1 == s3));
    }
}

s1 == s2? false
s1 == s3? true

<!– User defined Service Class where we are having a DAO’s instant variable and a setter injection will occur with the following code –>
<bean id=”userservices” class=”com.nr.ana.services.UserServices”>
<property name=”userDAO”>
<ref bean=”userDAO” />
</property>
</bean>
</beans>

Q: How to synchronize arraylist?

A:by using the method Collections.synchronizedList(); ,

ArrayList al=new ArrayList();

al.add(“lolo”);

al.add(“polo”);

al.add(“hai”);

Collections.synchronizedList(al);

Q:In How Many Ways can you create an object for a class in java?

A:There are four ways in which we can create an object for a class in java

Using New Operator: like Test t=new Test();

Using newInstance(): like Test t=(Test)Class.forName(“”).newInstance();

Using Clone: like

Test x=new Test();

Test t=x.clone();

Using Object Deserialization : like ObjectInputStream istream=new ObjectInputStream(some inputStream);

Q: Can we create constructor for an abstract class?

A: Yes , we can create Constructor for abstaract class. The constructor will be invoked while instantiating its subclass object. The constructor can be explicitly by using super keyword.

Q: Is it possible to override static method?

A: No it is not possible to override a static method. This because there is only 1 instance of a static method.

Q: How can container knows that JSP has been changed ? ex: I created one.jsp and the result has been displayed. Next i modified one.jsp and got the new result. but how can container know that one.jsp has got changed?

A: By checking the “time stamp” of the jsp file

Q: What’s the difference between the methods sleep() and wait()

A: The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.

Q: State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.

A: public : Public class is visible in other packages, field is visible everywhere (class must be public too)

private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.

protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.

default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.

Q: What is static in java?

A: Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can’t override a static method with a nonstatic method. In other words, you can’t change a static method into an instance method in a subclass.

Q: Difference between HashMap and HashTable?

A: The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.

Q: What if the main method is declared as private?

A: The program compiles properly but at runtime it will give “Main method not public.” message.

Q: If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?

A: It is empty. But not null.

Q: How can one prove that the array is not null but empty using one line of code?

A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.

Q: What are Checked and UnChecked Exception?

A:A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.

Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream’s read() method·

Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn’t force client programmers either to catch the

exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String’s charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be.

Q: What are different types of inner classes?

A:Nested top-level classes, Member classes, Local classes, Anonymous classes

Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.

Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only to static variables.There can also be inner interfaces. All of these are of the nested top-level variety.

Member classes – Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.

Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a

more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.

Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.

Q: What is the difference between declaring a variable and defining a variable?

A: In declaration we just mention the type of the variable and it’s name. We do not initialize it. But defining means declaration + initialization.

e.g String s; is just a declaration while String s = new String (“abcd”); Or String s = “abcd”; are both definitions.

Q: Give a simplest way to find out the time a method takes for execution without using any profiling tool?

A:  Read the system time just before the method is invoked and immediately after method returns. Take the time difference, which will give you the time taken by a method for execution.

To put it in code…

long start = System.currentTimeMillis ();

method ();

long end = System.currentTimeMillis ();

System.out.println (“Time taken for execution is ” + (end – start));

Remember that if the time taken for execution is too small, it might show that it is taking zero milliseconds for execution. Try it on a method which is big enough, in the sense the one which is doing considerable amout of processing.

Q:  How to call a procedure having more than one out parameter ?

package proceduretest;

import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.sql.Types;

import oracle.jdbc.driver.OracleTypes;

public class CallingProcedure {
public static void main(String[] args) throws Exception {
Connection con = null;
try {
Class.forName(“oracle.jdbc.driver.OracleDriver”);
con = DriverManager.getConnection(
“jdbc:oracle:thin:@localhost:1521:XE”, “jyoti”, “mishra”);

/**
*
*
* Procedure For Below ResultSets
* ===================================
* create or replace PROCEDURE
* getName(emp__CURSOR1 OUT SYS_REFCURSOR,emp__CURSOR2 OUT
* SYS_REFCURSOR, salary out NUMBER, empnumber in number)
* AS
* BEGIN
* OPEN emp__CURSOR1 FOR SELECT ename FROM EMP where
* empno=empnumber;
*
* OPEN emp__CURSOR2 FOR SELECT * FROM EMP ;
*
* SELECT SAL INTO salary FROM EMP WHERE EMPNO=empnumber;
*
* END;
*
*
*
*
*/
CallableStatement cstmt = con
.prepareCall(“{call GETNAME(?,?,?,?)}”);
cstmt.registerOutParameter(1, OracleTypes.CURSOR);
cstmt.registerOutParameter(2, OracleTypes.CURSOR);
cstmt.registerOutParameter(3, Types.FLOAT);
cstmt.setInt(4, 7369);
boolean resultsAvailable = cstmt.execute();
System.out.println(“Resultset available ” + resultsAvailable);
ResultSet rs1 = (ResultSet) cstmt.getObject(1);
System.out.println(“Empname  ” + “Name  ” + ” JOB”);
while (rs1.next()) {
System.out.println(“Employee Nmae having ID 7369 : “
+ rs1.getString(1) + ” “);
}
System.out.println(“=====================\n\n”);
/*rs1 = (ResultSet) cstmt.getObject(2);
while (rs1.next()) {
System.out.print(” ” + rs1.getInt(1) + ” “);
System.out.print(rs1.getString(2) + ” “);
System.out.print(rs1.getString(3) + ” “);
System.out.print(rs1.getInt(4) + ” “);
System.out.print(rs1.getDate(5) + ” “);
System.out.print(rs1.getInt(6) + ” “);
System.out.print(rs1.getInt(7) + ” “);
System.out.println(rs1.getInt(8) + ” “);
}*/
Float sal = cstmt.getFloat(3);
System.out.println(“Employee Salary having ID 7369 : ” + sal);
} catch (ClassNotFoundException cnf) {
System.out.println(cnf.getMessage());
}

}
}

Well when we use hql statement that will select all the attributes from the POJO class, no problem to type cast the retuen type to corresponding POJO Class reference. As below example shows:
List list = session.createQuery(“from Contact c “).list();
for (Iterator iterator = list.iterator(); iterator.hasNext();) {
Contact contact = (Contact) iterator.next();
System.out.print(“First Name ==>> ” + contact.getFirstName());
System.out.println(“Last Name ==>> ” + contact.getLastName());
}

This time the “list” contain object of type Contact. So no problem in type casting it to Contact class (pojo) reference. But what will happened if we select specified attributes like below:

List list = session.createQuery(“select c.firstName, c.lastName from Contact c “).list();
for (Iterator iterator = list.iterator(); iterator.hasNext();) {
Contact contact = (Contact) iterator.next();
System.out.print(“First Name ==>> ” + contact.getFirstName());
System.out.println(” Last Name ==>> ” + contact.getLastName());
}

This time it will through a java.lang.ClassCastException. Beacuse this time the list contains type Object. So it is not possible to type cast to POJO class reference.
But in some cases we required pojo class object. At that time constructor will be usefull in HQL statements. Create a constructor using those attributes which you required in select statements. Like below:
Contact.java
package jyoti.ssis.hibernate;
/** * @author Jyoti Ranjna * *
* Java Class to map to the datbase Contact Table
*/
public class Contact {
private String firstName;
private String lastName;
private String email;
private long id;
/* Default Constructor
* */
public Contact() {
}
/** required parametrized constructor
* @param firstName
* @param lastName
*/
public Contact(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
/** * @return Email
*/
public String getEmail() {
return email;
}
/** * @return First Name
*/
public String getFirstName() {
return firstName;
}
/** * @return Last name
*/
public String getLastName() {
return lastName;
}
/** * @param string Sets the Email
*/
public void setEmail(String string) {
email = string;
}
/** * @param string Sets the First Name
*/
public void setFirstName(String string) {
firstName = string;
}
/** * @param string sets the Last Name
*/
public void setLastName(String string) {
lastName = string;
}
/** * @return ID Returns ID
*/
public long getId() {
return id;
}
/** * @param l Sets the ID
*/
public void setId(long l) {
id = l;
}
}

Corresponding Mapping file
contact.hbm.xml

<?xml version=”1.0″?>
<!DOCTYPE hibernate-mapping PUBLIC
“-//Hibernate/Hibernate Mapping DTD 3.0//EN”
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd>

<hibernate-mapping>
<class name=”jyoti.ssis.hibernate.Contact” table=”CONTACT”>
<id name=”id” column=”ID”><generator></id>
<property name=”firstName”><column name=”FIRSTNAME”></property>
<property name=”lastName”><column name=”LASTNAME”></property>
<property name=”email”><column name=”EMAIL”></property>
</class>
</hibernate-mapping>

Finally the main class where we will use the constructor for getting the pojo class object

SelectHQLExampleUsingConstructor.java
package jyoti.ssis.hibernate;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/** * @author Jyoti Ranjan * *
Select HQL Example Using Constructor
*/

public class SelectHQLExampleUsingConstructor {
static SessionFactory sessionFactory =null;
public static void main(String[] args) {
Session session = null;
try {
//Get Session From Session Factory
session = getSession();
String s = “Jyoti”;
List list = session.createQuery( “select new Contact(c.firstName, c.lastName)from Contact c where c.firstName like ‘”+s+”‘”).list();
for (Iterator iterator = list.iterator(); iterator.hasNext();) {
Contact contact = (Contact) iterator.next();
System.out.print(“First Name ==>> ” + contact.getFirstName());
System.out.println(” Last Name ==>> ” + contact.getLastName());
}
} catch (Exception e) {
System.out.println(e.getMessage());
} finally {
if (session != null) session.close();
}
}
public static Session getSession(){
//Create HibernateSessionFactory
if(sessionFactory==null){
sessionFactory = new Configuration().configure().buildSessionFactory();
}
return sessionFactory.openSession();
}
}

Finally the hibernate configuration file
hibernate.cfg.xml

<?xml version=’1.0′ encoding=’utf-8′?>
<!DOCTYPE hibernate-configuration PUBLIC
“-//Hibernate/Hibernate Configuration DTD//EN”
http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd>

<hibernate-configuration>
<session-factory>
<property name=”hibernate.connection.pool_size”>10</property>
<property name=”show_sql”>true</property>
<property name=”dialect”>org.hibernate.dialect.MySQLDialect</property>
<property name=”hibernate.hbm2ddl.auto”>update</property>
<property name=”myeclipse.connection.profile”>mysql</property>
<property name=”connection.url”>jdbc:mysql://localhost:3306/hibernate</property>
<property name=”connection.username”>root</property>
<property name=”connection.password”>root</property>
<property name=”connection.driver_class”>com.mysql.jdbc.Driver</property>
<mapping resource=”jyoti/ssis/hibernate/contact.hbm.xml”></session-factory>
</hibernate-configuration>

Run application by setting hibernate required jar files in class path. The out put of the application should come like this on eclipse console:
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment). log4j:WARN Please initialize the log4j system properly.
Hibernate: select contact0_.FIRSTNAME as col_0_0_, contact0_.LASTNAME as col_1_0_ from CONTACT contact0_ where (contact0_.FIRSTNAME like ‘Jyoti’)
First Name ==>> Jyoti Last Name ==>> Ranjan

I am using c3po connection pool and the settings in the hibernate.cfg.xml file for c3po is as follows

<property name=”c3p0.min_size”>5</property>
<property name=”c3p0.max_size”>20</property>
<property name=”c3p0.timeout”>1800</property>
<property name=”c3p0.max_statements”>50</property>
<property name=”connection.provider_class”>org.hibernate.connection.C3P0ConnectionProvider</property>

But what happened after a certain amount of connection idle time, i am getting the following error. I solve the error as mentioned following:

Error Message From Log File

WARN TP-Processor2 org.hibernate.util.JDBCExceptionReporter – SQL Error: 0, SQLState: 08003
ERROR TP-Processor2 org.hibernate.util.JDBCExceptionReporter – No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:

** BEGIN NESTED EXCEPTION **

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException
MESSAGE: The last packet successfully received from the server was34330 seconds ago.The last packet sent successfully to the server was 34330 seconds ago, which is longer than the server configured value of ‘wait_timeout’. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property ‘autoReconnect=true’ to avoid this problem.

STACKTRACE:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was34330 seconds ago.The last packet sent successfully to the server was 34330 seconds ago, which is longer than the server configured value of ‘wait_timeout’. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property ‘autoReconnect=true’ to avoid this problem.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3246)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1917)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2542)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1734)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1885)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:375)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:308)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:153)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1106)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
at com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO.validateAdmin(AdminloginDAO.java:172)
at com.softidsolutions.mypaydayadvancenow.admin.services.AdminServices.validateAdmin(AdminServices.java:17)
at com.softidsolutions.mypaydayadvancenow.admin.action.AdminLoginAction.execute(AdminLoginAction.java:34)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:200)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:773)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:703)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:895)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.net.SocketException: Software caused connection abort: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3227)
… 41 more

** END NESTED EXCEPTION **

ERROR TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Validating Login Failed , Error is could not execute query
INFO TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Time is: 05-29-2009 11:18:35 AM CDT
INFO TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Closing Session
INFO TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Time is: 05-29-2009 11:18:35 AM CDT
INFO TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Validating AdminLogin
INFO TP-Processor2 com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO – Time is: 05-29-2009 11:18:53 AM CDT
WARN TP-Processor2 org.hibernate.util.JDBCExceptionReporter – SQL Error: 0, SQLState: 08003
ERROR TP-Processor2 org.hibernate.util.JDBCExceptionReporter – No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:

** BEGIN NESTED EXCEPTION **

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException
MESSAGE: The last packet successfully received from the server was34330 seconds ago.The last packet sent successfully to the server was 34330 seconds ago, which is longer than the server configured value of ‘wait_timeout’. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property ‘autoReconnect=true’ to avoid this problem.

STACKTRACE:

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was34330 seconds ago.The last packet sent successfully to the server was 34330 seconds ago, which is longer than the server configured value of ‘wait_timeout’. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property ‘autoReconnect=true’ to avoid this problem.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3246)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1917)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2542)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1734)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1885)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:375)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:308)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:153)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1106)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
at com.softidsolutions.mypaydayadvancenow.admin.dao.AdminloginDAO.validateAdmin(AdminloginDAO.java:172)
at com.softidsolutions.mypaydayadvancenow.admin.services.AdminServices.validateAdmin(AdminServices.java:17)
at com.softidsolutions.mypaydayadvancenow.admin.action.AdminLoginAction.execute(AdminLoginAction.java:34)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:200)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:773)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:703)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:895)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.net.SocketException: Software caused connection abort: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3227)
… 41 more

** END NESTED EXCEPTION **

SOLUTION

You need to create a properties file like c3p0.properties and place the file in the class path of your project.

Place the following code in that file

c3p0.testConnectionOnCheckout=true

What the following code will do is:

it will check whether the connection is disconnected. If the connection is disconnected it will reconnect automatically.