Document Information


Part I Introduction

1.  Overview

2.  Using the Tutorial Examples

Part II The Web Tier

3.  Getting Started with Web Applications

4.  Java Servlet Technology

What Is a Servlet?

The Example Servlets

Troubleshooting Duke's Bookstore Database Problems

Servlet Life Cycle

Handling Servlet Life-Cycle Events

Defining the Listener Class

Specifying Event Listener Classes

Handling Servlet Errors

Sharing Information

Using Scope Objects

Controlling Concurrent Access to Shared Resources

Accessing Databases

Initializing a Servlet

Writing Service Methods

Getting Information from Requests

Constructing Responses

Filtering Requests and Responses

Programming Filters

Programming Customized Requests and Responses

Specifying Filter Mappings

Invoking Other Web Resources

Including Other Resources in the Response

Transferring Control to Another Web Component

Accessing the Web Context

Maintaining Client State

Accessing a Session

Associating Objects with a Session

Notifying Objects That Are Associated with a Session

Session Management

Session Tracking

Further Information about Java Servlet Technology

5.  JavaServer Pages Technology

6.  JavaServer Pages Documents

7.  JavaServer Pages Standard Tag Library

8.  Custom Tags in JSP Pages

9.  Scripting in JSP Pages

10.  JavaServer Faces Technology

11.  Using JavaServer Faces Technology in JSP Pages

12.  Developing with JavaServer Faces Technology

13.  Creating Custom UI Components

14.  Configuring JavaServer Faces Applications

15.  Internationalizing and Localizing Web Applications

Part III Web Services

16.  Building Web Services with JAX-WS

17.  Binding between XML Schema and Java Classes

18.  Streaming API for XML

19.  SOAP with Attachments API for Java

Part IV Enterprise Beans

20.  Enterprise Beans

21.  Getting Started with Enterprise Beans

22.  Session Bean Examples

23.  A Message-Driven Bean Example

Part V Persistence

24.  Introduction to the Java Persistence API

25.  Persistence in the Web Tier

26.  Persistence in the EJB Tier

27.  The Java Persistence Query Language

Part VI Services

28.  Introduction to Security in the Java EE Platform

29.  Securing Java EE Applications

30.  Securing Web Applications

31.  The Java Message Service API

32.  Java EE Examples Using the JMS API

33.  Transactions

34.  Resource Connections

35.  Connector Architecture

Part VII Case Studies

36.  The Coffee Break Application

37.  The Duke's Bank Application

Part VIII Appendixes

A.  Java Encoding Schemes

B.  About the Authors



Finalizing a Servlet

When a servlet container determines that a servlet should be removed from service (for example, when a container wants to reclaim memory resources or when it is being shut down), the container calls the destroy method of the Servlet interface. In this method, you release any resources the servlet is using and save any persistent state. The following destroy method releases the database object created in the init method described in Initializing a Servlet:

public void destroy() {
    bookDB = null;

All of a servlet’s service methods should be complete when a servlet is removed. The server tries to ensure this by calling the destroy method only after all service requests have returned or after a server-specific grace period, whichever comes first. If your servlet has operations that take a long time to run (that is, operations that may run longer than the server’s grace period), the operations could still be running when destroy is called. You must make sure that any threads still handling client requests complete; the remainder of this section describes how to do the following:

  • Keep track of how many threads are currently running the service method.

  • Provide a clean shutdown by having the destroy method notify long-running threads of the shutdown and wait for them to complete.

  • Have the long-running methods poll periodically to check for shutdown and, if necessary, stop working, clean up, and return.

Tracking Service Requests

To track service requests, include in your servlet class a field that counts the number of service methods that are running. The field should have synchronized access methods to increment, decrement, and return its value.

public class ShutdownExample extends HttpServlet {
    private int serviceCounter = 0;
    // Access methods for serviceCounter
    protected synchronized void enteringServiceMethod() {
    protected synchronized void leavingServiceMethod() {
    protected synchronized int numServices() {
        return serviceCounter;

The service method should increment the service counter each time the method is entered and should decrement the counter each time the method returns. This is one of the few times that your HttpServlet subclass should override the service method. The new method should call super.service to preserve the functionality of the original service method:

protected void service(HttpServletRequest req,
                    HttpServletResponse resp)
                    throws ServletException,IOException {
    try {
        super.service(req, resp);
    } finally {

Notifying Methods to Shut Down

To ensure a clean shutdown, your destroy method should not release any shared resources until all the service requests have completed. One part of doing this is to check the service counter. Another part is to notify the long-running methods that it is time to shut down. For this notification, another field is required. The field should have the usual access methods:

public class ShutdownExample extends HttpServlet {
    private boolean shuttingDown;
    //Access methods for shuttingDown
    protected synchronized void setShuttingDown(boolean flag) {
        shuttingDown = flag;
    protected synchronized boolean isShuttingDown() {
        return shuttingDown;

Here is an example of the destroy method using these fields to provide a clean shutdown:

public void destroy() {
    /* Check to see whether there are still service methods /*
    /* running, and if there are, tell them to stop. */
    if (numServices() > 0) {

    /* Wait for the service methods to stop. */
    while(numServices() > 0) {
        try {
        } catch (InterruptedException e) {

Creating Polite Long-Running Methods

The final step in providing a clean shutdown is to make any long-running methods behave politely. Methods that might run for a long time should check the value of the field that notifies them of shutdowns and should interrupt their work, if necessary.

public void doPost(...) {
    for(i = 0; ((i < lotsOfStuffToDo) &&
         !isShuttingDown()); i++) {
        try {
        } catch (InterruptedException e) {