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java - 如何在 JAR 文件中的 Jetty 服务器中启用 JSP？

问题描述

tl;dr：我怎样才能为这个项目启用 JSP 支持（你也可以下载为 zip 文件）？

我正在尝试使用 Jetty 创建一个简单的“hello world”Web 应用程序，我对目前所拥有的非常满意。重要的文件是：

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>io.happycoding</groupId>
  <artifactId>app-engine-hello-world</artifactId>
  <version>1</version>

  <properties>
    <!-- App Engine currently supports Java 11 -->
    <maven.compiler.source>11</maven.compiler.source>
    <maven.compiler.target>11</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <jetty.version>9.4.31.v20200723</jetty.version>

    <!-- Project-specific properties -->
    <exec.mainClass>io.happycoding.ServerMain</exec.mainClass>
    <googleCloudProjectId>YOUR_PROJECT_ID_HERE</googleCloudProjectId>
  </properties>

  <dependencies>
    <!-- Java Servlets API -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
    </dependency>

    <!-- Jetty -->
    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-server</artifactId>
      <version>${jetty.version}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-annotations</artifactId>
      <version>${jetty.version}</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <!-- Copy static resources like html files into the output jar file. -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.7</version>
        <executions>
          <execution>
            <id>copy-web-resources</id>
            <phase>compile</phase>
            <goals><goal>copy-resources</goal></goals>
            <configuration>
              <outputDirectory>
                ${project.build.directory}/classes/META-INF/resources
              </outputDirectory>
              <resources>
                <resource><directory>./src/main/webapp</directory></resource>
              </resources>
            </configuration>
          </execution>
        </executions>
      </plugin>

      <!-- Package everything into a single executable jar file. -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>3.2.4</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals><goal>shade</goal></goals>
            <configuration>
              <createDependencyReducedPom>false</createDependencyReducedPom>
              <transformers>
                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                  <mainClass>${exec.mainClass}</mainClass>
                </transformer>
              </transformers>
            </configuration>
          </execution>
        </executions>
      </plugin>

      <!-- App Engine plugin for deploying to the live site. -->
      <plugin>
        <groupId>com.google.cloud.tools</groupId>
        <artifactId>appengine-maven-plugin</artifactId>
        <version>2.2.0</version>
        <configuration>
          <projectId>${googleCloudProjectId}</projectId>
          <version>1</version>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

ServerMain.java

package io.happycoding;

import java.net.URL;
import org.eclipse.jetty.annotations.AnnotationConfiguration;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.DefaultServlet;
import org.eclipse.jetty.webapp.Configuration;
import org.eclipse.jetty.webapp.WebAppContext;
import org.eclipse.jetty.webapp.WebInfConfiguration;

/**
 * Starts up the server, including a DefaultServlet that handles static files,
 * and any servlet classes annotated with the @WebServlet annotation.
 */
public class ServerMain {

  public static void main(String[] args) throws Exception {

    // Create a server that listens on port 8080.
    Server server = new Server(8080);
    WebAppContext webAppContext = new WebAppContext();
    server.setHandler(webAppContext);

    // Load static content from inside the jar file.
    URL webAppDir =
        ServerMain.class.getClassLoader().getResource("META-INF/resources");
    webAppContext.setResourceBase(webAppDir.toURI().toString());

    // Enable annotations so the server sees classes annotated with @WebServlet.
    webAppContext.setConfigurations(new Configuration[]{ 
      new AnnotationConfiguration(),
      new WebInfConfiguration(), 
    });

    // Look for annotations in the classes directory (dev server) and in the
    // jar file (live server)
    webAppContext.setAttribute(
        "org.eclipse.jetty.server.webapp.ContainerIncludeJarPattern", 
        ".*/target/classes/|.*\\.jar");

    // Handle static resources, e.g. html files.
    webAppContext.addServlet(DefaultServlet.class, "/");

    // Start the server! 
    server.start();
    System.out.println("Server started!");

    // Keep the main thread alive while the server is running.
    server.join();
  }
}

索引.jsp

<%@ page import="java.util.Date" %>
<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Google Cloud Hello World</title>
  </head>
  <body>
    <h1>Google Cloud Hello World</h1>
    <p>This is a sample HTML file. Click <a href="/hello">here</a> to see content served from a servlet.</p>
    <p>Learn more at <a href="https://happycoding.io">HappyCoding.io</a>.</p>
    <p>The current time is: <%= new Date().toString() %></p>
  </body>
</html>

服务器启动并完美呈现 HTML。Servlet 也可以工作。但是当我尝试像上面那样使用 JSP 时，我看到 JSP 代码呈现在 HTML 中，而不是被解析为 Java。

html中的jsp

我试过谷歌搜索，但我发现的每个教程都是通过创建一个单独的 WAR 文件来工作的。我的服务器是从 JAR 文件启动的，我试图使代码尽可能简单，所以我尽量避免使用单独的 WAR 文件。

我可以对我的pom.xml文件和我的ServerMain.java文件进行一些小的更改以启用 JSP 吗？

标签： javamavenjspservlets

解决方案

要在嵌入式 Jetty 服务器中启用 JSP 支持，您需要做两件事，修改您的项目pom.xml文件以包含必要的依赖项，并在您的类中配置JettyJspServlet相关的 Jetty 内容。ServerMain

首先，在您的项目中包含以下依赖项pom.xml。他们将为 JSP 和 JSTL 提供支持：

<dependency>
    <groupId>org.eclipse.jetty</groupId>
    <artifactId>apache-jsp</artifactId>
    <version>${jetty.version}</version>
</dependency>

<dependency>
    <groupId>org.eclipse.jetty</groupId>
    <artifactId>apache-jstl</artifactId>
    <version>${jetty.version}</version>
    <type>pom</type>
</dependency>

然后，使用这个ServerMain类的修改版本：

package io.happycoding;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;

import org.apache.tomcat.util.scan.StandardJarScanner;
import org.eclipse.jetty.annotations.AnnotationConfiguration;
import org.eclipse.jetty.apache.jsp.JettyJasperInitializer;
import org.eclipse.jetty.jsp.JettyJspServlet;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.DefaultServlet;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.eclipse.jetty.util.component.AbstractLifeCycle;
import org.eclipse.jetty.webapp.Configuration;
import org.eclipse.jetty.webapp.WebAppContext;
import org.eclipse.jetty.webapp.WebInfConfiguration;

/**
 * Starts up the server, including a DefaultServlet that handles static files,
 * and any servlet classes annotated with the @WebServlet annotation.
 */
public class ServerMain {

  public static void main(String[] args) throws Exception {

    // Create a server that listens on port 8080.
    Server server = new Server(8080);
    WebAppContext webAppContext = new WebAppContext();
    server.setHandler(webAppContext);

    // Load static content from inside the jar file.
    URL webAppDir =
        ServerMain.class.getClassLoader().getResource("META-INF/resources");
    webAppContext.setResourceBase(webAppDir.toURI().toString());

    // Enable annotations so the server sees classes annotated with @WebServlet.
    webAppContext.setConfigurations(new Configuration[]{
        new AnnotationConfiguration(),
        new WebInfConfiguration(),
    });

    // Look for annotations in the classes directory (dev server) and in the
    // jar file (live server)
    webAppContext.setAttribute(
        "org.eclipse.jetty.server.webapp.ContainerIncludeJarPattern",
        ".*/target/classes/|.*\\.jar");

    // Handle static resources, e.g. html files.
    webAppContext.addServlet(DefaultServlet.class, "/");

    // Configure JSP support.
    enableEmbeddedJspSupport(webAppContext);

    // Start the server! 
    server.start();
    System.out.println("Server started!");

    // Keep the main thread alive while the server is running.
    server.join();
  }

  /**
   * Setup JSP Support for ServletContextHandlers.
   * <p>
   *   NOTE: This is not required or appropriate if using a WebAppContext.
   * </p>
   *
   * @param servletContextHandler the ServletContextHandler to configure
   * @throws IOException if unable to configure
   */
  private static void enableEmbeddedJspSupport(ServletContextHandler servletContextHandler) throws IOException
  {
    // Establish Scratch directory for the servlet context (used by JSP compilation)
    File tempDir = new File(System.getProperty("java.io.tmpdir"));
    File scratchDir = new File(tempDir.toString(), "embedded-jetty-jsp");

    if (!scratchDir.exists())
    {
      if (!scratchDir.mkdirs())
      {
        throw new IOException("Unable to create scratch directory: " + scratchDir);
      }
    }
    servletContextHandler.setAttribute("javax.servlet.context.tempdir", scratchDir);

    // Set Classloader of Context to be sane (needed for JSTL)
    // JSP requires a non-System classloader, this simply wraps the
    // embedded System classloader in a way that makes it suitable
    // for JSP to use
    ClassLoader jspClassLoader = new URLClassLoader(new URL[0], ServerMain.class.getClassLoader());
    servletContextHandler.setClassLoader(jspClassLoader);

    // Manually call JettyJasperInitializer on context startup
    servletContextHandler.addBean(new JspStarter(servletContextHandler));

    // Create / Register JSP Servlet (must be named "jsp" per spec)
    ServletHolder holderJsp = new ServletHolder("jsp", JettyJspServlet.class);
    holderJsp.setInitOrder(0);
    holderJsp.setInitParameter("logVerbosityLevel", "DEBUG");
    holderJsp.setInitParameter("fork", "false");
    holderJsp.setInitParameter("xpoweredBy", "false");
    holderJsp.setInitParameter("compilerTargetVM", "1.8");
    holderJsp.setInitParameter("compilerSourceVM", "1.8");
    holderJsp.setInitParameter("keepgenerated", "true");
    servletContextHandler.addServlet(holderJsp, "*.jsp");
  }

  /**
   * JspStarter for embedded ServletContextHandlers
   *
   * This is added as a bean that is a jetty LifeCycle on the ServletContextHandler.
   * This bean's doStart method will be called as the ServletContextHandler starts,
   * and will call the ServletContainerInitializer for the jsp engine.
   *
   */
  public static class JspStarter extends AbstractLifeCycle implements ServletContextHandler.ServletContainerInitializerCaller
  {
    JettyJasperInitializer sci;
    ServletContextHandler context;

    public JspStarter (ServletContextHandler context)
    {
      this.sci = new JettyJasperInitializer();
      this.context = context;
      this.context.setAttribute("org.apache.tomcat.JarScanner", new StandardJarScanner());
    }

    @Override
    protected void doStart() throws Exception
    {
      ClassLoader old = Thread.currentThread().getContextClassLoader();
      Thread.currentThread().setContextClassLoader(context.getClassLoader());
      try
      {
        sci.onStartup(null, context.getServletContext());
        super.doStart();
      }
      finally
      {
        Thread.currentThread().setContextClassLoader(old);
      }
    }
  }
}

如您所见，与前面代码的主要区别在于enableEmbeddedJspSupport在配置嵌入式 Jetty 服务器时包含对新方法的方法调用main。

该enableEmbeddedJspSupport方法和伴随类是您可以在此 Github 存储库中的类JspStarter中找到的代码的改编版本。Main

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