?? servlet-config.xtp
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<s1 title="Servlet"><p>Servlets are Java classes which service HTTP requests. The onlyrequirement for writing a servlet is that it implements thejavax.servlet.Servlet interface.</p><p>Servlets are loaded from the classpath like all Java classes.Normally, users put servlets in <var/WEB-INF/classes/> so Resin willautomatically reload them when they change.</p><p><a href='jsp.xtp'>JSP</a> pages are implemented asServlets, and tend to be more efficient for pages with lots of text.</p><s2 title='Examples'><s3 title='Configuring the web.xml'><p>The following is a complete working web.xml to run this example.</p><p>The <var/servlet-mapping/> tells Resin that the URL<var//hello/> should invoke the <var/hello-world/> servlet.</p><p>The <var/servlet/> tells Resin that <var/hello-world/> uses the<var/test.HelloWorld/> class and that the value of the <var/greeting/>init parameter is <var/Hello World/>.</p><example title='WEB-INF/web.xml'><web-app> <servlet-mapping url-pattern='/hello' servlet-name='hello-world'/> <servlet servlet-name='hello-world' servlet-class='test.HelloWorld'> <init-param greeting='Hello, World'/></web-app></example><p>The Java code, <var/HelloWorld.java/> belongs in</p><def>$app-dir/WEB-INF/classes/test/HelloWorld.java</def><p>Or, if you're compiling the servlet yourself, the class file belongs in</p><def>$app-dir/WEB-INF/classes/test/HelloWorld.class</def><p>Following is the actual servlet code. It just prints a trivialHTML page filled with the greeting specified in the web.xml.</p><p><var/init()/> and <var/destroy()/> are included mostly forillustration. Resin will call <var/init()/> when it starts the servletand <var/destroy/> before Resin destroys it.</p><example>package test;import java.io.*;import javax.servlet.*;import javax.servlet.http.*;public class HelloWorld extends HttpServlet { private String greeting; public void init() throws ServletException { greeting = getInitParameter("greeting"); } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); out.println("<title>" + greeting + "</title>"); out.println("<h1>" + greeting + "</h1>"); } public void destroy() { // nothing to do }}</example></s3><s3 title='Servlet Example for JSP Programmers'><p>Because Resin compiles JSP pages into servlets, programmers familiarwith JSP can start writing servlets fairly easily. The following templatecan be used to see how to write a servlet for someone familiar with JSP.</p><example>package test;import java.io.*;import javax.servlet.*;import javax.servlet.http.*;public class HelloWorld extends HttpServlet { public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { PrintWriter out = response.getWriter(); ServletContext application = getServletContext(); HttpSession session = request.getSession(); try { // <var/code goes here/> // The equivalent of jsp:include: // request.getRequestDispatcher("/inc.jsp").include(request, response); } catch (ServletException e) { throw e; } catch (Exception e) { throw new ServletException(e); } }}</example></s3><s3 title='Using Databases from a Servlet'><p>The following is a sample design pattern for getting new databaseconnections. The <var/try ... finally/> block is very important. Withoutthe close in the finally block, Resin's database pool can loose connections.</p><p>Configuring the database is described in the<a href="db-config.xtp">database configuration</a> page.</p><example title="TestDatabase.java">package test;import java.io.*;import java.sql.*;import javax.servlet.*;import javax.servlet.http.*;import javax.naming.*;import javax.sql.*;public class TestDatabase extends HttpServlet { DataSource pool; public void init() throws ServletException { try { Context env = (Context) new InitialContext().lookup("java:comp/env"); pool = (DataSource) env.lookup("jdbc/test"); if (pool == null) throw new ServletException("`jdbc/test' is an unknown DataSource"); } catch (NamingException e) { throw new ServletException(e); } } public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); Connection conn = null; try { conn = pool.getConnection(); // <var/code for the servlet using the database goes here/> rs.close(); stmt.close(); } catch (SQLException e) { throw new ServletException(e); } finally { try { if (conn != null) conn.close(); } catch (SQLException e) { } } }}</example></s3></s2><s2 title="Servlet Configuration"><defun title="init" version="Resin 2.1.3"><p>Configures servlets using bean-style initialization.Each entry in an <init> tag will configure a <code/setFoo/>method in a Servlet. JSP EL expressions are allowed.</p><p>The <code/init(config)/> method is called afterall the bean setters are called.</p><example title="Bean-style Configuration"><servlet servlet-name='test.HelloWorld'> <init> <greeting>Hello, ${host.url}</greeting> </init></servlet></example><example title="HelloWorld bean">public HelloWorld extends GenericServlet { private String _greeting; public void setGreeting(String greeting) { _greeting = greetin; } public void service(ServletRequest req, ServletResponse res) throws IOException, ServletException { PrintWriter out = res.getWriter(); out.println("Greeting: " + _greeting); }}</example></defun><defun title='init-param'><p>Initializes servlet variables. <code/servlet-param/>defines initial values for <code/getServletConfig().getInitParameter("foo")/>.</p><p>The full servlet 2.2 syntax is supported and allows a simple shortcut.</p><example><web-app id='/'><servlet servlet-name='test.HelloWorld'> <init-param foo='bar'/> <init-param> <param-name>baz</param-name> <param-value>value</param-value> </init-param></servlet></web-app></example></defun><defun title="load-on-startup"><p>If present, starts the servlet when the server starts.</p><example><web-app id='/'><servlet servlet-name='hello' servlet-class='test.HelloWorld'> <load-on-startup/></servlet></web-app></example></defun><defun title='run-at' version='Resin 1.1'><p>If present, calls the servlet's <var/service()/> methodat the specified times.<run-at> lets servlet writers execute periodic tasks without worryingabout creating a new Thread.</p><p>The value is a list of 24-hour times when theservlet should be automatically executed. To run the servlet every 6hours, you could use:</p><example><servlet servlet-name='test.HelloWorld'> <run-at>0:00, 6:00, 12:00, 18:00</run-at></servlet></example><p>If the hour is omitted, the servlet runs every hour at thespecified minute. To run the server every 15 minutes, you could use:</p><example><servlet servlet-name='test.HelloWorld'> <run-at>:00, :15, :30, :45</run-at></servlet></example></defun><defun title='servlet'><p>Defines a servlet alias for later mapping.</p><deftable><tr><th>Attribute<th>Description<tr><td>servlet-name<td>The servlet's name (alias)<tr><td>servlet-class<td>The servlet's class (defaults to servlet-name)<tr><td>init-param<td>Initialization parameters<tr><td>load-on-startup<td>Initializes the servlet when the server starts.<tr><td>run-at<td>Times to execute the servlet automatically</deftable><p>The following example defines a servlet alias 'hello'</p><example><web-app id='/'><servlet-mapping url-pattern='/hello.html' servlet-name='hello'/><servlet servlet-name='hello' servlet-class='test.HelloWorld'> <init-param title='Hello, World'/></servlet><servlet servlet-name='cron' servlet-class='test.DailyChores'> <run-at>3:00</run-at></servlet></web-app></example></defun><defun title='servlet-class'><p>Class of the servlet. The CLASSPATH for servlets includesthe WEB-INF/classes directory and all jars in the WEB-INF/lib directory.</p></defun><defun title="servlet-name"><p>Alias of the servlet, uniquely naming a servlet configuration.Several <servlet> configurations might configure the sameservlet class with different <init-param> values. Each willhave a separate servlet-name.</p><example title="Multiple Servlets"><web-app> <servlet servlet-name='foo-a'> <servlet-class>test.FooServlet</servlet-class> <init-param name='foo-a sample'/> </servlet> <servlet servlet-name='foo-b'> <servlet-class>test.FooServlet</servlet-class> <init-param name='foo-b sample'/> </servlet></web-app></example></defun><defun title="servlet-mapping"><p>Maps from a URL to the servlet to execute. The servlet-mappinghas a url-pattern to match the URL and a servlet-name to match theconfigured servlet.</p><example title="typical servlet-mapping"><servlet> <servlet-name>hello</servlet-name> <servlet-class>test.HelloServlet</servlet-class></servlet><servlet-mapping> <url-pattern>/hello/*</url-pattern> <servlet-name>hello</servlet-name></servlet-mapping></example><p>Resin allows for a shortcut combining the servlet andthe servlet mapping:</p><example title="shortcut servlet-mapping"><servlet-mapping url-pattern="/hello/*" servlet-class="test.HelloServlet"/></example></defun><defun title="url-pattern" version="Servlet 2.2"><p>Matches a set of URLs for servlet-mapping.</p><deftable><tr><th width='25%'>Pattern<th>Description<tr><td>/foo/bar.html<td>Matches exactly the /foo/bar.html URL.<tr><td>/foo/*<td>Matches /foo and any children<tr><td>*.foo<td>Matches any URL with a .foo extension<tr><td>/<td>Replaces the default servlet.</deftable><p><var///> defines a default handler and <var//*/> defines a prefix handler.<var//*/> will override extension handlers like <var/*.foo/>. <var///>will only be used if no other pattern matches.</p><p>No default. Either url-pattern or url-regexp is required.</p></defun></s2></s1>?? 快捷鍵說明
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