Servlets 简明教程

Servlets - Packaging

涉及 WEB-INF 子目录的 Web 应用程序结构对于所有 Java Web 应用程序都是标准的，并由 servlet API 规范指定。给定顶层目录名称为 myapp。这个目录结构看起来像这样 -

The web application structure involving the WEB-INF subdirectory is standard to all Java web applications and specified by the servlet API specification. Given a top-level directory name of myapp. Here is how this directory structure looks like −

/myapp
   /images
   /WEB-INF
      /classes
      /lib

WEB-INF 子目录包含应用程序的部署描述符，名为 web.xml。所有 HTML 文件都应保存在顶层目录（即 myapp）中。对于管理员用户，您会发现 ROOT 目录作为父目录。

The WEB-INF subdirectory contains the application’s deployment descriptor, named web.xml. All the HTML files should be kept in the top-level directory which is myapp. For admin user, you would find ROOT directory as parent directory.

Creating Servlets in Packages

WEB-INF/classes 目录包含所有 servlet 类和其他类文件，其结构与其包名称相匹配。例如，如果您有 com.myorg.MyServlet 的完全限定类名，那么该 servlet 类必须位于以下目录中 -

The WEB-INF/classes directory contains all the servlet classes and other class files, in a structure that matches their package name. For example, If you have a fully qualified class name of com.myorg.MyServlet, then this servlet class must be located in the following directory −

/myapp/WEB-INF/classes/com/myorg/MyServlet.class

以下示例使用包名为 com.myorg 创建 MyServlet 类

Following is the example to create MyServlet class with a package name com.myorg

// Name your package
package com.myorg;

// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class MyServlet extends HttpServlet {

   private String message;

   public void init() throws ServletException {
      // Do required initialization
      message = "Hello World";
   }

   public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

      // Set response content type
      response.setContentType("text/html");

      // Actual logic goes here.
      PrintWriter out = response.getWriter();
      out.println("<h1>" + message + "</h1>");
   }

   public void destroy() {
      // do nothing.
   }
}

Compiling Servlets in Packages

编译包中提供的类并没有什么不同。最简单的办法是将您的 Java 文件保存在完全限定的路径中，如上所述，该类将保存在 com.myorg 中。还需要将此目录添加到 CLASSPATH 中。

There is nothing much different to compile a class available in package. The simplest way is to keep your java file in fully qualified path, as mentioned above class would be kept in com.myorg. You would also need to add this directory in CLASSPATH.

假设您的环境已正确设置，请转到 <Tomcat-installationdirectory> /webapps/ROOT/WEB-INF/classes 目录并按如下方式编译 MyServlet.java

Assuming your environment is setup properly, go in <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes directory and compile MyServlet.java as follows

$ javac MyServlet.java

如果 servlet 依赖于任何其他库，则还必须在 CLASSPATH 上包含这些 JAR 文件。我仅包含 servlet-api.jar JAR 文件，因为我在 Hello World 程序中未使用任何其他库。

If the servlet depends on any other libraries, you have to include those JAR files on your CLASSPATH as well. I have included only servlet-api.jar JAR file because I’m not using any other library in Hello World program.

此命令行使用随 Sun Microsystems Java 软件开发工具包 (JDK) 提供的内置 javac 编译器。为了使此命令正常工作，您必须在 PATH 环境变量中包含您正在使用的 Java SDK 的位置。

This command line uses the built-in javac compiler that comes with the Sun Microsystems Java Software Development Kit (JDK). For this command to work properly, you have to include the location of the Java SDK that you are using in the PATH environment variable.

如果一切顺利，上述编译会在同一目录中生成 MyServlet.class 文件。下一节将说明如何将已编译 servlet 部署到生产中。

If everything goes fine, above compilation would produce MyServlet.class file in the same directory. Next section would explain how a compiled servlet would be deployed in production.

Packaged Servlet Deployment

默认情况下，servlet 应用程序位于路径 <Tomcat-installationdirectory>/webapps/ROOT 中，类文件将驻留在 <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes 中。

By default, a servlet application is located at the path <Tomcat-installationdirectory>/webapps/ROOT and the class file would reside in <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/classes.

如果您有 com.myorg.MyServlet 的完全限定类名，那么此 servlet 类必须位于 WEB-INF/classes/com/myorg/MyServlet.class 中，并且您需要在位于 <Tomcat 安装目录>/webapps/ROOT /WEB-INF/ 中的 web.xml 文件中创建以下条目：

If you have a fully qualified class name of com.myorg.MyServlet, then this servlet class must be located in WEB-INF/classes/com/myorg/MyServlet.class and you would need to create following entries in web.xml file located in <Tomcat-installationdirectory>/webapps/ROOT/WEB-INF/

<servlet>
   <servlet-name>MyServlet</servlet-name>
   <servlet-class>com.myorg.MyServlet</servlet-class>
</servlet>

<servlet-mapping>
   <servlet-name>MyServlet</servlet-name>
   <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

上述条目将创建标签中可用的 <web-app>…​</web-app> web.xml 文件内。此表格中可能已经存在各种条目，但不必担心。

Above entries to be created inside <web-app>…​</web-app> tags available in web.xml file. There could be various entries in this table already available, but never mind.

您几乎完成了，现在让我们使用 <Tomcat-installationdirectory>\bin\startup.bat (在 Windows 中) 或 <Tomcat-installationdirectory>/bin/startup.sh (在 Linux/Solaris 等中) 启动 Tomcat 服务器，最后在浏览器的地址栏中键入 http://localhost:8080/MyServlet 。如果一切顺利，您将获得以下结果 −

You are almost done, now let us start tomcat server using <Tomcat-installationdirectory>\bin\startup.bat (on windows) or <Tomcat-installationdirectory>/bin/startup.sh (on Linux/Solaris etc.) and finally type http://localhost:8080/MyServlet in browser’s address box. If everything goes fine, you would get following result −

Hello World