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

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

Finalizing a Servlet

Tracking Service Requests

Notifying Methods to Shut Down

Creating Polite Long-Running Methods

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



Sharing Information

Web components, like most objects, usually work with other objects to accomplish their tasks. There are several ways they can do this. They can use private helper objects (for example, JavaBeans components), they can share objects that are attributes of a public scope, they can use a database, and they can invoke other web resources. The Java Servlet technology mechanisms that allow a web component to invoke other web resources are described in Invoking Other Web Resources.

Using Scope Objects

Collaborating web components share information by means of objects that are maintained as attributes of four scope objects. You access these attributes using the [get|set]Attribute methods of the class representing the scope. Table 4-3 lists the scope objects.

Table 4-3 Scope Objects

Scope Object


Accessible From

Web context


Web components within a web context. See Accessing the Web Context.



Web components handling a request that belongs to the session. See Maintaining Client State.


Subtype of javax.servlet.ServletRequest

Web components handling the request.



The JSP page that creates the object. See Using Implicit Objects.

Figure 4-1 shows the scoped attributes maintained by the Duke’s Bookstore application.

Figure 4-1 Duke’s Bookstore Scoped Attributes

Diagram of Duke's Bookstore scoped attributes. Session attributes are currency and cart, web context attributes are hitCounter, bookDB, orderCounter.

Controlling Concurrent Access to Shared Resources

In a multithreaded server, it is possible for shared resources to be accessed concurrently. In addition to scope object attributes, shared resources include in-memory data (such as instance or class variables) and external objects such as files, database connections, and network connections.

Concurrent access can arise in several situations:

  • Multiple web components accessing objects stored in the web context.

  • Multiple web components accessing objects stored in a session.

  • Multiple threads within a web component accessing instance variables. A web container will typically create a thread to handle each request. If you want to ensure that a servlet instance handles only one request at a time, a servlet can implement the SingleThreadModel interface. If a servlet implements this interface, you are guaranteed that no two threads will execute concurrently in the servlet’s service method. A web container can implement this guarantee by synchronizing access to a single instance of the servlet, or by maintaining a pool of web component instances and dispatching each new request to a free instance. This interface does not prevent synchronization problems that result from web components accessing shared resources such as static class variables or external objects. In addition, the Servlet 2.4 specification deprecates the SingleThreadModel interface.

When resources can be accessed concurrently, they can be used in an inconsistent fashion. To prevent this, you must control the access using the synchronization techniques described in the Threads lesson in The Java Tutorial, Fourth Edition, by Sharon Zakhour et al. (Addison-Wesley, 2006).

The preceding section showed five scoped attributes shared by more than one servlet: bookDB, cart, currency, hitCounter, and orderCounter. The bookDB attribute is discussed in the next section. The cart, currency, and counters can be set and read by multiple multithreaded servlets. To prevent these objects from being used inconsistently, access is controlled by synchronized methods. For example, here is the Counter class, located at tut-install/javaeetutorial5/examples/web/bookstore1/src/java/com/sun/bookstore1/util/:

public class Counter {
    private int counter;
    public Counter() {
        counter = 0;
    public synchronized int getCounter() {
        return counter;
    public synchronized int setCounter(int c) {
        counter = c;
        return counter;
    public synchronized int incCounter() {

Accessing Databases

Data that is shared between web components and is persistent between invocations of a web application is usually maintained by a database. Web components use the Java Persistence API to access relational databases. The data for Duke’s Bookstore is maintained in a database and is accessed through the database access class tut-install/javaeetutorial5/examples/web/bookstore1/src/java/com/sun/bookstore1/database/BookDBAO. For example, ReceiptServlet invokes the BookDBAO.buyBooks method to update the book inventory when a user makes a purchase. The buyBooks method invokes buyBook for each book contained in the shopping cart, as shown in the following code.

public void buyBooks(ShoppingCart cart) throws OrderException{

    Collection items = cart.getItems();
    Iterator i = items.iterator();
    try {
        while (i.hasNext()) {
            ShoppingCartItem sci = (ShoppingCartItem);
            Book bd = (Book)sci.getItem();
            String id = bd.getBookId();
            int quantity = sci.getQuantity();
            buyBook(id, quantity);
    } catch (Exception ex) {
        throw new OrderException("Commit failed: " +

public void buyBook(String bookId, int quantity)
     throws OrderException {

    try {
        Book requestedBook = em.find(Book.class, bookId);
        if (requestedBook != null) {
            int inventory = requestedBook.getInventory();
            if ((inventory - quantity) >= 0) {
                int newInventory = inventory - quantity;
            } else{
                throw new OrderException("Not enough of "
                     + bookId + " in stock to complete order.");
    } catch (Exception ex) {
        throw new OrderException("Couldn’t purchase book: "
             + bookId + ex.getMessage());

To ensure that the order is processed in its entirety, the call to buyBooks is wrapped in a single transaction. In the following code, the calls to the begin and commit methods of UserTransaction mark the boundaries of the transaction. The call to the rollback method of UserTransaction undoes the effects of all statements in the transaction so as to protect the integrity of the data.

try {
} catch (Exception ex) {
    try {
    } catch(Exception e) {
        System.out.println("Rollback failed: "+e.getMessage());
    orderCompleted = false;}