@WebServlet注解的示例分享

@WebServlet注解的简介

`@WebServlet`是Java Servlet 3.0引入的一个注解
   用于声明一个Servlet类，
      而无需在`web.xml`中进行配置
	  它简化Web应用的部署和维护

@WebServlet注解使用说明

-功能:将一个类标识为 Servlet，
      并指定其访问路径。
-使用条件:
  - 必须继承`HttpServlet`
  - 必须重写`doGet()`或`doPost()`等方法
- 使用方法:直接标注在类上
- 适用版本:Servlet 3.0+(Tomcat 7+)

例1：最简单Hello World Servlet

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/html;charset=UTF-8");
        resp.getWriter().write("Hello, @WebServlet!");
    }
}
 
访问地址：`http://localhost:8080/your-app/hello`

例2:带多个 URL 映射的 Servlet<?h2>

@WebServlet({"/user/list", "/api/users"})
public class UserListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.getWriter().write("用户列表数据...");
    }
}
 

以上示例支持两个路径访问

- `http://localhost:8080/your-app/user/list`
- `http://localhost:8080/your-app/api/users`

例3:带初始化参数Servlet

@WebServlet(name = "InitServlet", urlPatterns = "/init", initParams = {
    @WebInitParam(name = "appName", value = "MyWebApp"),
    @WebInitParam(name = "version", value = "1.0")
})
public class InitServlet extends HttpServlet {
    @Override
    public void init() {
        String appName = getServletConfig().getInitParameter("appName");
        System.out.println("应用名称：" + appName);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.getWriter().write("初始化参数已加载");
    }
}

@WebServlet注解注意事项

@WebServlet注解与web.xml配置对比

使用web.xml配置方式
 
<servlet>
    <servlet-name>HelloServlet</servlet-name>
    <servlet-class>com.example.HelloServlet</servlet-class>
    <init-param>
        <param-name>appName</param-name>
        <param-value>MyWebApp</param-value>
    </init-param>
</servlet>

<servlet-mapping>
    <servlet-name>HelloServlet</servlet-name>
    <url-pattern>/hello</url-pattern>
</servlet-mapping>