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<document> <header> <product>resin</product> <title>A Hello, World Servlet</title> <description><p>A trivial "hello, world" servlet</p></description> <type>tutorial</type> <tutorial-startpage>hello</tutorial-startpage> </header> <body> <localtoc/><s1 title="Files in this tutorial"><deftable><tr> <th>File</th> <th>Description</th></tr><tr> <td><viewfile-link file="WEB-INF/resin-web.xml"/></td> <td>resin-web.xml configuration</td></tr><tr> <td><viewfile-link file="WEB-INF/classes/test/HelloServlet.java"/></td> <td>The Hello, World servlet.</td></tr></deftable></s1><s1><p>Servlets are the pure Java solution to handle web requests. Manyapplication will use servlets instead of JSP and others will use servletsin conjunction with JSP. Experienced JSP programmers use servletsin conjunction with JSP to create clearer and simpler applications.The servlets handle Java processing: form handing, calculation anddatabase queries. JSP formats the results.</p><p>Servlets belong in <var>WEB-INF/classes</var>. On this machine,the source is in Java source in <var>WEB-INF/classes</var>.<!--<jsp:expression>application.getRealPath("/WEB-INF/classes")</jsp:expression></var>.-->WEB-INF/classes is the standard locationfor servlets and other Java classes. Resin automatically reloads andrecompiles servlets, beans, and classes placed in WEB-INF/classes.You should make some changes and add errors to become familiar with Resin'srecompilation and the error reporting.</p><p>Create the following servlet in<var>WEB-INF/classes/test/HelloServlet.java</var> with your favoritetext editor: notepad, emacs, vi, or whatever.<!--(On this machine,<var><jsp:expression> application.getRealPath("/WEB-INF/classes/test/HelloServlet.java")</jsp:expression></var>)--></p><example title="Example: WEB-INF/classes/test/HelloServlet.java">package test;import java.io.*;import javax.servlet.http.*;import javax.servlet.*;public class HelloServlet extends HttpServlet { public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { PrintWriter out = res.getWriter(); out.println("Hello, world!"); out.close(); }}</example><p>Now browse the servlet at<!--<a href="hello"><jsp:expression>request.getContextPath() + "/hello"</jsp:expression></a>.--><a href="hello">http://localhost:8080/resin-doc/tutorial/hello</a>.Resin will automatically compiles the servlet for you.Browsing servlets differs from page browsing becauseyou're executing a servlet class, not looking at a page.The <var>/hello</var> URL is configured for the hello, world servlet below.</p></s1><s1 title="Configuration"><p>Configuration for the servlet is in the <var>WEB-INF/web.xml</var> file.</p><p>The servlet needs to be configured and it needs to be mappedto a URL. The <a config-tag="servlet"/> tagconfigures the servlet. In our simple example, we just need tospecify the class name for the servlet.</p><p>The <a config-tag="servlet-mapping"/>tag specifies the URLs which will invoke the servlet. In our case,the <var>/hello</var> URL invokes the servlet. Because the tutorial<a href="doc|webapp.xtp">webapp</a> is a sub-URL like<var>/doc/servlet/tutorial/helloworld</var>, the actual URL to invokethe servlet is the combination of the two.</p><example title="Example: WEB-INF/web.xml"><web-app xmlns="http://java.sun.com/xml/ns/j2ee" version="2.4" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http:/java.sun.com/dtd/web-app_2_3.dtd"> <servlet> <servlet-name>hello</servlet-name> <servlet-class>test.HelloServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping></web-app></example><p>Resin allows a short cut for the XML configuration in the example above;you can use XML attributes in place of elements. TheServlet 2.4 standard uses only elements. So the servlet-mappingconfiguration following the Servlet 2.4 standard would look like:</p><example title="Example: WEB-INF/resin-web.xml"><web-app xmlns="http://caucho.com/ns/resin"> <servlet-mapping url-pattern="/hello" servlet-class="test.HelloServlet"/></web-app></example><p>The two are entirely equivalent. For larger configurations,using attributes makes the resin.conf or web.xml more readable.</p><deftable><tr> <th>tag</th> <th>meaning</th></tr><tr> <td>web-app</td> <td>Web application top-level tag.</td></tr></deftable><p>The <var>xmlns="http://caucho.com/ns/resin"</var> lets Resinvalidate the web.xml configuration. The validator will catch mosterrors in the web.xml.</p></s1> </body></document>⌨️ 快捷键说明
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