Life Without NetBeans

Transcription

1 Life Without NetBeans Part C Web Applications Background What is a WAR? A Java web application consists a collection of Java servlets and regular classes, JSP files, HTML files, JavaScript files, images, etc. All of these resources are often bundled together in a Web ARchive a file with a.war extension. This.war file is then deployed to a web server to make the application available. Differences between a WAR and a JAR The main difference between a WAR and a JAR is that a WAR contains everything needed to run the application, including external libraries (.jar files). So, a WAR can contain JAR s, whereas a JAR cannot contain other JAR s. In addition, a JAR requires a manifest specifying the application s entry point (the class containing the main method), but a WAR does not. This is because a web application automatically loads the file index.html. Structure of a WAR A.war file contains everything needed to run the application. Inside the file, the root level contains the HTML, JavaScript, images, and any other non Java resources. The Java resources, including both the application s Java sources as well as external JAR s, must be inside a folder called WEB INF. Every web server Glassfish, Tomcat, Jetty, etc. automatically looks for that folder to find the compiled code. It is also recommended that the internal and external Java code be separated by placing the external JAR s in a folder called lib. So, the structure looks like this: Life Without NetBeans Part C Page 1 of 8

2 Example The.war file shown below was built by NetBeans. You can see how the files are organized according to the structure shown above. D:\temp>jar tf MenuBuilder_JSON.war META INF/ META INF/MANIFEST.MF WEB INF/ WEB INF/classes/ WEB INF/classes/menubuilder/ WEB INF/classes/restaurantmenu/ WEB INF/lib/ js/ WEB INF/classes/menubuilder/CreateMenu.class WEB INF/classes/restaurantmenu/Menu.class WEB INF/classes/restaurantmenu/MenuItem.class WEB INF/classes/restaurantmenu/MenuSection.class WEB INF/lib/gson 2.5.jar appetizers.csv desserts.csv entrees.csv index.html js/scripts.js menustyle.css results.html sections.html Life Without NetBeans Part C Page 2 of 8

3 The web.xml File In the diagram above, note the existence of a file called web.xml. Also note that the example.war file shown does not contain such a file. Here is the explanation: Prior to version 3 of the servlet specification, the web.xml file was required. The main function of the file is to specify the servlet mapping i.e., the directions that tell the server which servlet corresponds to which name. (For example, if you want the URL to a servlet to be MyServlet, you must tell the server which.class file that name corresponds to something like mypackage.myservlet.) As of version 3, you have a choice: you can still use web.xml, or you can specify the mapping with an annotation instead (which is what happened in the example shown above). You might have noticed that when you create a new servlet in NetBeans, it asks you for the mapping and asks if you want to create a web.xml file. If you say you don t want the file, then NetBeans inserts a mapping annotation something = "GetItems", urlpatterns = {"/GetItems"}) public class GetItems extends HttpServlet { // your code } So, if the server you are deploying the application on supports Servlets version 3, then you can use annotations; otherwise, you ll need the web.xml file. We will look at both approaches. Life Without NetBeans Part C Page 3 of 8

4 Example 1 Objective : Deploy a.war file to a web server. Background NetBeans automatically bundles your application into a.war file and stores it in the dist folder in the project folder. This file is now independent of NetBeans and can be deployed to any web server. Exercise 1. In the starter code, note the file named FizzBuzz.war. This is a complete web application. You will now deploy it to Glassfish. 2. Open a command prompt in administrator mode. (On Windows, right click the command prompt icon, and select Run as administrator.) 3. Navigate to the Glassfish installation directory, then glassfish, then bin it will be something like C:\Program Files\glassfish 4.1\glassfish\bin. 4. Execute the command and wait a few moments for the server to start: asadmin start domain 5. Open a web browser and enter localhost:8080 in the URL window. You should see a page telling you that the Glassfish server is running, and there should be a link to the administration console. 6. Go to Glassfish s admin console either by clicking the link or by entering localhost:4848 in the URL window. 7. Select the Applications node, and then select Deploy. 8. Select the option to upload a.war file, then browse to where the file is and upload it. The application should now be listed in admin console. 9. Open a new browser instance and enter localhost:8080/fizzbuzz in the URL window. You should see the application running. 10. Choose an application you have written in NetBeans. Deploy the WAR for that application (you ll find it in the dist folder) in the manner just described. 11. When you are finished, stop the server with the command: Lessons asadmin stop domain A.war file is a complete application that can be deployed to any web server. Life Without NetBeans Part C Page 4 of 8

5 Example 2 Objective : Create and deploy a WAR. Background To create.war file, we follow a process similar to that for.jar files: (1) gather all the components together; (2) compile the Java classes to a separate folder; (3) Use the jar command to build the archive. Exercise Assemble and Compile 1. In an empty folder, create the following folder structure. 2. Copy everything from the starter code folder AirportSearch to sources. You should now have the following in your main folder. Life Without NetBeans Part C Page 5 of 8

6 3. Navigate to the folder sources\java\controller and display the contents of the file AirportServlet.java. Note that the servlet class has annotation. This is the mapping that tells the server where to find the servlet. Therefore, we don t need a web.xml file. (Notice that there isn t one in the folder contents shown above.) 4. We will now compile the Java classes. Navigate back one level to the java directory. Execute the command: javac d "..\..\build\web INF\classes" cp ".;..\lib\gson 2.5.jar" controller\*.java You will see several error messages all having to do with the fact that the compiler can t find the Servlet libraries. Unlike other Java classes like Scanner or String, the Servlet classes are not part of the core Java language, but are contained in external.jar files. These files must be included in the classpath at compilation time. 5. Navigate to C:\Program Files and search for the servlet JAR with the command: dir javax.servlet api.jar /s Take note of the location of that file. (On my own computer, it is C:\Program Files\glassfish 4.1\glassfish\modules ) 6. Copy the file javax.servlet api.jar to sources\java. Now try compiling again with the JAR in the classpath, as follows: javac d "..\..\build\web INF\classes" cp ".;..\lib\gson 2.5.jar;javax.servlet api.jar" controller\*.java The compilation should succeed. Verify that the classes have been placed in the appropriate folders in build\web INF\classes. We are now ready to proceed with building the WAR. Build and Deploy 7. Navigate to the build folder. 8. Recall from the diagram earlier that the web pages should be at the root level, and everything else should be inside WEB INF. So: Life Without NetBeans Part C Page 6 of 8

7 a. Copy everything in the the web folder (but not the web folder itself) to the build folder. b. Copy the file gson 2.5.jar from sources\lib to build\web INF\lib. 9. Your build folder should now contain the following: 10. Build the WAR with the command (note the. at the end it means everything in the current folder ): jar cf AirportSearch.war. 11. (Optional) Display the contents of the.war file with the jar tf command. 12. Deploy the application to the server (as described in Example 1), and then run the application. Make sure it is working correctly. Lessons A.war file is easy to build using the jar command, provided the correct folder structure is used. In Servlet version 3, annotation can be used in the Java source code, rather than creating a web.xml file. When compiling the source code, the path to the required servlet.jar files must be specified. When creating the WAR, the application s.jar files are included, but the servlet.jar files do not need to be included (because the web server will have them). Life Without NetBeans Part C Page 7 of 8

8 Example 3 Objective : Create and deploy a WAR that uses a web.xml file. Background In servlet versions earlier than 3, a web.xml file is used to specify servlet mappings. Exercise 13. Examine the file web.xml in the AirportSearchOld\web\WEB INF folder. 14. The <servlet> tag specifies which Java class corresponds to the servlet with the name AirportServlet. 15. The <servlet mapping> tag specifies how the servlet s path should be specified in the URL. 16. Putting those two pieces together means that the servlet with the specified class name is mapped to the specified URL pattern. 17. Repeat the exercise from Example 2 with this version of the application. Make sure that web.xml gets included in the WAR and that it is inside WEB INF. Final Exercise 1. Choose a web application that you have written. 2. Using the techniques in this tutorial, compile, build, and deploy your application, starting with the source files. Do not use NetBeans or use any pre compiled code. Life Without NetBeans Part C Page 8 of 8