Developing JSPs and Servlets with Netbeans <inlinegraphic fileref="logo.gif"/>

Developing JSPs and Servlets with Netbeans <inlinegraphic fileref="logo.gif"/> NickShrine

N.R.Shrine@cs.bham.ac.uk

2004 Nick Shrine Printable (pdf) version, XML source Netbeans comes with a built-in Tomcat server for development of JSPs and Servlets. It also has templates for Web Applications, JSP pages and Servlet classes and automatically updates your web application delployment descriptor (web.xml) when you add new servlets. It is also possible to run web applications in the debugger. Creating a new Web Application Start a new project and create and mount a directory for your web application. With the above directory selected, select: File → New → JSPs & Servlets → Web Module. Hit Next, the target directory in the subsequent dialog should be the one you mounted above. Now hit Finish. Now you should have a view in your Filesystem explorer like this: You put your .html and .jsp files in the top level directory, any file references in your JSP/servlets are relative to this directory. WEB-INF/classes is where you put your servlet classes. WEB-INF/lib is where you put any .jar files required by your application e.g. postgresql.jar for web applications that access a Postgresql database. WEB-INF/web is your web.xml file (double-click to edit). You can ignore the META-INF directory. Netbeans also remounts WEB-INF/classes at the bottom to give you a shortcut to your servlet package hierarchy. Creating a new JSP page To create a JSP page select the top level folder in the explorer then do File → New → JSPs & Servlets → JSP. Hit Next. Enter a name for your JSP (without .jsp extension). You can select a subfolder to put it in if you want to organise your pages into subfolders. Then hit Finish: Netbeans creates a skeleton JSP page comprising of little more than the <head> and <body> tags and a couple of commented-out sample bean directives. I have added the <h1> and <p> lines in the screenshot below. To run your JSP page select it in the explorer or source editor and hit F6 or the button. You will either see the page in Netbeans internal browser: or you can point Mozilla at the relevent URL: Netbeans 3.6 uses port 8084 for Tomcat so the URL will be of the format http://localhost:8084/<your web app>/<your jsp or servlet> Creating a new Servlet To create a servlet, select the WEB-INF/classes folder or the corresponding mount at the bottom, then do File → New → JSPs & Servlets → Servlet. Hit Next Enter a name for your servlet. You must specify a package for your servlet classes. Hit Next. Specify a URL mapping for your servlet. It can be useful to prefix servlet URLs with /servlet/ for later deployment on web servers such as Apache where this prefix can be used for deciding which pages to forward to web container such as Tomcat for processing. You can also specify any servlet initialisation parameters that you can then access from the servlet's init() method. Hit Finish Netbeans creates a skeleton servlet with init(), destroy(), doGet(), doPost() and getServletInfo() methods. By default the familiar doGet() and doPost() methods are both forwarded to a single common processRequest() method as shown above. But you can delete this if you want and code the appropriate doGet() and doPost() method bodies as appropriate. To run your servlet select it in the explorer or the source editor and hit F6 or the button and Netbeans should start Tomcat. Fire up your browser and point it at the relevant URL thus: The <filename>web.xml</filename> file The web.xml file is the Web Application Deployment Descriptor, which defines which servlets should be run for certain URLs and some other parameters of your web application. Netbeans creates one for you when you create a new web application and it looks something like this: The format of the URL-to-servlet mappings is described here. You can see that Netbeans has automatically added <servlet> and <servlet-mapping> entries for MyServlet we just created above. The <session-config> contains a definition for the time in minutes before a user's session times out (in this case 30 minutes) and a <welcome-file-list> section describing which files will be loaded as the default home page for the web application. In this case it will try index.jsp, index.html and finally if these don't exist index.htm. When you create a new servlet you can set up URL mappings in the New-Servlet dialogs and Netbeans will add the appropriate entries to your web.xml, but you are free to edit these by hand. Adding <filename>.jar</filename> files to your application If your web applications needs additional libraries such as for database access then copy the corresponding .jar file to your project's WEB-INF/lib directory (e.g. postgresql.jar) and then right-click on WEB-INF/lib and select Refresh Folder and the file will be added to your web application's classpath. I have not found an easy way to copy files from within Netbeans. If you copy and paste a jar file between mounts it tends to unpack the jar file, so I usually copy them in by hand e.g.: cp /bham/common/java/lib/postgresql.jar ~/work/mywebapp/WEB-INF/lib/ Then subsequently, right-click on WEB-INF/lib and select Refresh Folder Restarting Tomcat If you edit your code, hitting (run) again will recompile and restart Tomcat. To restart the whole web application select WEB-INF in the explorer and hit (run). Any altered JSP/servlets will be recompiled and redeployed. Occasionally not all changes will be registered, such as if you manually edit web.xml or edit tag libraries. In which case I manually restart Tomcat by going to the Runtime tab and right-click on the node Server Registry → Tomcat 5 Servers → http://localhost:8084 and select Start / Stop Server Debugging JSPs and Servlets Set any breakpoints where you would like execution to halt in your JSP or Servlet code by moving the cursor to the appropriate line in the editor and either hit Shift-F8 or right-click → Toggle Breakpoint. To debug the current JSP or Servlet that you are editing hit the button whilst the cursor is in the editor pane. To debug the whole web application hit the button whilst WEB-INF is selected in the Explorer. The application will run until a breakpoint is encountered. The green line shows the current line to be executed and the execution can be controlled by the buttons at the top: The buttons left to right are Stop, Pause, Continue, Step Over, Step Into, Step Out and Run to Cursor. (Pause is greyed out as the program is already paused at the breakpoint). In the panes at the bottom you can see the Call Stack, the values of Local Variables (you can expand objects to look at member variables) and the values of any Watches you have set. You can set a new watch on a variable by right-clicking on it and selecting New Watch. For debugging web applications Netbeans also provides a HTTP Monitor so that you can look at the values of parameters in the actual HTTP requests. To see the servlet code generated for a JSP page (remember JSPs are just templates for servlets created automatically by the container), right click anywhere in the source of the JSP and select View Servlet. Exporting your Web Application To create a web application .war file to deploy on external JSP/Servlet containers, right-click on WEB-INF and select Export WAR file... then give it a name in the file dialog.