204 WebSphere Studio Application Developer Version 5 Programming Guide Application Developer wizards not only support you in creating servlets, JSPs, and JavaBeans, but they also compile the Java code and store the class files in the correct folders for publishing to your application servers. In addition, as the wizards generate project resources, the deployment descriptor file, web.xml , is updated with the appropriate configuration information for the servlets that are created. You can test the resulting project resources within the Application Developer using the WebSphere Test Environment, or any other configured server that supports the chosen J2EE specification level. Working with servlets Servlets are flexible and scalable server-side Java components based on the Sun Microsystems Java Servlet API, as defined in the Sun Microsystems Java Servlet Specification. For J2EE 1.3, the supported API is Servlet 2.3. Servlets generate dynamic content by responding to Web client requests. When an HTTP request is received by the application server, the server determines which servlet is responsible for answering that request (based on the requested URI) and forwards the request to that servlet. The servlet then performs its logic and builds the response HTML that is returned back to the Web client. Application Developer provides the necessary features to make servlets easy to develop and integrate into your Web application. Without leaving your Workbench, you can develop, debug, and deploy them. You can set breakpoints within servlets, and step through the code. You can make changes that are dynamically folded into the running servlet on a running server, without having to restart the server each time. Adding a servlet to your Web project Application Developer provides a servlet wizard to assist you in adding servlets to your Web applications. To start it, select File -> New -> Other . Select Web -> Servlet and click Next . Alternatively, you can switch to the J2EE Navigator view, select the Java Source folder in your Web project folder, and select New -> Servlet from its context menu. The wizard starts with the dialog shown in Figure 7-26. Chapter 7. Developing Web applications 205 Figure 7-26 New servlet wizard (page 1) The wizard’s first page will require you to fill out the following information: Folder The source folder of your Web project. In our case, it is \ItsoProGuideBasicWeb\Java Source. Java package The package in which the servlet class will be created. For our example, it should be itso.basicweb.control. Class Name The servlet’s class name. We will implement the ListAccounts servlet. Superclass Usually, and this is true to our example, you will select the javax.servlet.http.HttpServlet as your servlet’s superclass. Application Developer requires you to select a class that implements the javax.servlet.Servlet interface. 206 WebSphere Studio Application Developer Version 5 Programming Guide Modifiers These are the usual Java class modifiers. We will go with public. Servlets can also be abstract or final, but not both. Options The only option that you have here is to have your servlet implement the SingleThreadModel interface. This option should only be selected for servlets that must have read/write state accessed during their service methods. The need to implement the SingleThreadModel interface probably indicates a poor design. Interfaces Which additional interfaces your servlet needs to implement. Model No models are available for simple servlets. Click Next to proceed to the wizard’s second page, shown in Figure 7-27. Figure 7-27 New servlet wizard (page 2) This page lets you select the appropriate method stubs to be created in the servlet code. These are the servlet’s life-cycle methods, along with its service methods specific to the HTTP protocol (the methods that start with “do”). Chapter 7. Developing Web applications 207 For our example, we need both doGet and doPost selected. Both are read methods. Usually, HTTP gets are used with direct links, when no information needs to be sent to the server. HTTP posts are typically used when information in a form has to be sent to the server. Only one instance of a servlet is created in the application server. If you want to perform any initialization when the servlet instance is created, select the init method to be created. This method is invoked after the servlet instance has been created and you can perform the initialization tasks. Another check box lets you select whether or not you want to generate stubs for the inherited abstract methods. You should select it if your servlet is concrete. Because constructors are not inherited in Java, you may also want to generate constructors that call their counterpart in the superclass. Finally, the wizard lets you choose whether or not to add the new servlet to the Web deployment descriptor. If you choose to do so, and we do for our sample application, you can also define initialization parameters and their values, and the URLs mapped to the servlet. We will stick to the default URL mapping suggested by the wizard, which equals the servlet name. You can now click Finish to complete the process. The servlet is generated and added to the project. In the J2EE Hierarchy view you can see the servlet and its mapping in the Web module. In the J2EE Navigator view you can see the servlet file ListAccounts.java inside the itso.basicweb.control package. An editor is opened, where you can view and edit the generated servlet source code. Editing the servlet Application Developer generates a skeleton servlet for you. Your task is now to add code to the servlet in order to implement the required behavior for your needs. The code is provided in: \sg246957\sampcode\dev-web\servlet Start by adding these import statements to the statements generated for you: import javax.servlet.http.HttpSession; import itso.bank.model.Customer; import itso.bank.model.Account; import itso.bank.facade.Banking; Next, change the doGet and doPost methods’ body to look like this: public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { performTask(req, resp); } 208 WebSphere Studio Application Developer Version 5 Programming Guide public void doPost(HttpServletReq request, HttpServletResponse resp) throws ServletException, IOException { performTask(req, resp); } As you can see, both methods call a third method, called performTask. Because both doGet and doPost are read methods, and the Java API for handling the request parameters is the same no matter the request type, this works fine. Finally, you need to code the performTask method (see Example 7-1). Example 7-1 Servlet performTask method public void performTask(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { try { // Parameters // Get input parameter and keep it on the HTTP session String customerNumber = req.getParameter("customerNumber "); HttpSession session = req.getSession(); if (customerNumber == null) customerNumber = (String) session.getAttribute("customerNumber"); else session.setAttribute("customerNumber", customerNumber); // Control logic - Create the new banking facade Banking banking = new Banking(); // Retrieve customer and related accounts Customer customer = banking.getCustomer(customerNumber); Account[] accounts = banking.getAccounts(customerNumber); // Response - Set the request attributes for future rendering req.setAttribute("customer", customer ); req.setAttribute("accounts", accounts ); // Call the presentation renderer getServletContext().getRequestDispatcher("listAccounts.jsp") .forward(req, resp); } catch (Exception e) { req.setAttribute("message", e.getMessage()); req.setAttribute("forward", "index.html"); getServletContext().getRequestDispatcher("showException.jsp") .forward(req, resp); } } Chapter 7. Developing Web applications 209 The performTask method is divided into three main sections:  The first section deals with the HTTP parameters. This servlet expects to either receive a parameter called customerNumber (underlined) or none at all. If the parameter is passed, we store it in the HTTP session for future use. If it is not passed, we look for it in the HTTP session, because it might have been stored there earlier. The parameter name equals the text field name in the index.html page.  The second section deals with the control logic. We create a new Banking facade and use it to get the customer object and the array of accounts for that customer.  Finally, the third and last section sees that the presentation renderer (listAccounts.jsp) gets the parameters it requires to perform its job (customer and accounts, both underlined). The parameters are passed in the request context, because they are no longer needed once this request is answered. We could have written the presentation code in the servlet if we wanted to do so. Instead, we chose to use JSPs, which were specially designed for that purpose. Servlets do not make very good Web presentation renderers, because writing HTML code in Java is cumbersome. Save your changes and close the source editor. Linking an HTML page to a servlet Before we write our JSP code, we complete the index.html file by linking it to the ListAccounts servlet that we have just created. Open the index.html file and switch to the Design view. Select the form element and open its properties view by selecting Properties on the form’s context menu. The form’s action should be the ListAccounts servlet. But you do not have to type that in yourself. Instead, click -> Servlet and select the ListAccounts servlet from the pop-up list. Remove the Web application context root: From: /ItsoProGuideBasicWeb/ListAccounts <=== absolute URL To: ListAccounts <=== relative URL Finally, make sure that the Post method is selected. The Attributes view is shown in Figure 7-28. 210 WebSphere Studio Application Developer Version 5 Programming Guide Figure 7-28 Form element attributes You could have added the link to the servlet in the Source view as the action attribute of the form: <FORM action="ListAccounts" method="post"> Save the page and close the editor. Links view Select index.html file and the Links view. You should see the files (CSS file and image) and links (servlet, URL) that are used by the HTML file (Figure 7-29). Figure 7-29 Links view Working with JSPs Now that we have managed to build our first static page and our first servlet controller, it is time to complete the cycle by writing our first JSP page: listAccounts.jsp. This page is responsible for presenting the list of accounts belonging to the given user. select servlet servlet Chapter 7. Developing Web applications 211 When an application server such as WebSphere Application Server processes a request that involves a JSP file, it performs the following actions:  Compiles the JSP file into executable Java code, if needed. If a previously compiled JSP class file can be found, and the source file is older than the compiled file, the application server does not have to recompile the JSP file.  Instantiates the JSP servlet, if needed. Because JSPs are just like any other servlet, there will probably be just one instance of each type in memory at the same time (unless they implement the javax.servlet.SingleThreadModel interface). So, if the JSP has already been processed in a previous request, chances are that resulting servlet object is still in memory and can be reused.  Sends the request to the JSP servlet for processing.  The JSP servlet renders the HTML result which is sent back to the Web client for output. JSP files are edited in Page Designer, the very same editor you used to edit the HTML page. When working with a JSP page, though, Page Designer has additional elements (JSP tags) that can be used, such as JavaBean references, expressions, and scriptlets containing Java code. Creating a JSP To create a JSP file, select the Web Content folder and select New -> JSP File to open the new JSP file wizard (Figure 7-30).  Because you had the Web Content folder selected when you started the wizard, the folder field comes filled in for you. Type the file name (listAccounts.jsp) into the appropriate field. You do not have to type the file extension, as it will be automatically added for you.  We will be using HTML as the markup language, so leave it as is. The options are the same as when you created a new HTML page.  If you select the Create as JSP Fragment check box, this file will be created as a fragment that can be added to another JSP file. Other JSP files can include JSP fragments using a JSP include directive. Creating a fragment causes the resulting file to end in a .jspf or .jsf extension. You will not be prompted for DOCTYPE information, because a fragment cannot stand alone as a Web page, and it would invalidate any JSP file that included it.  We want the wizard to generate code without using any special models, so let the model field be set to none. Your other option would be to generate a Struts JSP page, but that will be left for Chapter 10, “Developing Struts applications” on page 293. 212 WebSphere Studio Application Developer Version 5 Programming Guide Figure 7-30 New JSP file wizard (page 1) Click Next to continue to the second page (Figure 7-31). Figure 7-31 New JSP file wizard (page 2) Chapter 7. Developing Web applications 213 The wizard’s second page lets you add tag libraries from a variety of sources. We do not have any tag libraries on our example, but the steps to add a tag library would be:  Click Add Tag Library to locate a tag library directive (TLD) file or a JAR file that contains a TLD file. TLD URIs can be located in one of the following places: –As a taglibname.tld file in the WEB-INF directory (most common). – Within a JAR file located in the project lib directory that contains \WEB-INF\taglibname.tld. – Within a JAR file external to the project. – In a loose .tld anywhere in the project.  Taglib files are referenced in the Web deployment descriptor (web.xml) file on the References page.  In the Select a tag library dialog, either select one of the available tag libraries, or click Import to locate and add a tag library to the list, and then select it. The dialog will automatically populate the informational fields that describe the tag library and its contents. You must specify a Prefix value. Click OK to add the tag library.  As you add tag libraries, the Available Custom Tags list box displays the declaration of the tag along with the tag library directive. If the selected TLD file is not registered in the web.xml file, it will be added automatically. We will skip working with tag libraries for now, so just click Next to proceed to the third page (Figure 7-32). Note: We will work with tag libraries in Chapter 10, “Developing Struts applications” on page 293. . 204 WebSphere Studio Application Developer Version 5 Programming Guide Application Developer wizards not only support you in creating servlets,. superclass. Application Developer requires you to select a class that implements the javax.servlet.Servlet interface. 206 WebSphere Studio Application Developer Version 5 Programming Guide Modifiers. will be left for Chapter 10, “Developing Struts applications” on page 293. 212 WebSphere Studio Application Developer Version 5 Programming Guide Figure 7-30 New JSP file wizard (page 1) Click