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环境

• Ubuntu 20.04.3

• Tomcat 8.5.54

• openjdk 11.0.11

安装Tomcat

• 更新源

$ apt-get update

• 安装 tomcat

$ apt-get install tomcat

• 启动 tomcat

$ sudo bash /opt/apache-tomcat-8.5.54/bin/startup.sh

配置Servlet

• webapps 目录结构

$ tree -d -L 1 webapps
webapps # web网站和app应用程序
├── docs # 文档
├── examples # 例子
├── host-manager # 主机管理
├── manager # 管理
├── yohann # 自定义的WEB应用目录
└── ROOT # 根目录

• yohann 目录结构

$ tree -L 2 yohann
yohann # 自定义的web应用目录
└── META-INF # 配置应用程序、扩展程序、类加载器和服务
└── WEB-INF # web应用的安全目录
    ├── classes # web应用的类库
    ├── lib # java的组件包
    └── web.xml # tomcat配置文件

• 修改 web.xml，代码如下：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
  version="3.1">

    <display-name>Hello, World Application</display-name>
    <description>
      This is a simple web application.
    </description>
    
    <servlet>
        <servlet-name>HelloWorldExample</servlet-name>
        <servlet-class>HelloWorldExample</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>HelloWorldExample</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

• 修改 ~/.zshrc 文件

export CLASSPATH=.:$JAVA_HOME/lib:$JAVA_HOME/jre/lib:/opt/apache-tomcat-8.5.54/lib/servlet-api.jar

编辑并保存 CLASSPATH 变量，添加 servlet-api.jar 这个包，然后执行 source ~/.zshrc使新配置生效。

• 新建 classes/HelloWorldExample.java，代码如下：

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class HelloWorldExample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
        throws IOException, ServletException
    {
        response.setContentType("text/html");
        response.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();
        out.print("您好,Tomact");
    }
}

• 编译 classes/HelloWorldExample.java

$ javac classes/HelloWorldExample.java;

• 重启 tomcat

$ sudo bash /opt/apache-tomcat-8.5.54/bin/shutdown.sh
$ sudo bash /opt/apache-tomcat-8.5.54/bin/startup.sh

• curl 访问

$ curl localhost:8080/yohann/hello
您好,Tomact%

Tomcat热加载

每次修改代码都要重启 tomcat 太麻烦了，可以通过 tomcat 热加载，无需重启 tomcat，自动加载 class。

• 新建 META-INF/context.xml，代码如下：

<?xml version='1.0' encoding='utf-8'?>
<Context reloadable="true">
    # 自动加载web.xml
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    # 自动加载class
    <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
</Context>

• 重启 tomcat

$ sudo bash /opt/apache-tomcat-8.5.54/bin/shutdown.sh
$ sudo bash /opt/apache-tomcat-8.5.54/bin/startup.sh

• 修改 classes/HelloWorldExample.java，代码如下：

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class HelloWorldExample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
        throws IOException, ServletException
    {
        response.setContentType("text/html");
        response.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();
        out.print("Hello,Tomact");
    }
}

• 编译 classes/HelloWorldExample.java

$ javac classes/HelloWorldExample.java;

• curl 访问

$ curl localhost:8080/yohann/hello
Hello,Tomact%