2. Servlet3.0注解方式 @WebServlet

web.xml配置还是比较麻烦，这次使用注解方式

编写servlet

import javax.servlet.ServletException;
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(value = "/test2")
public class ServletTest2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=utf-8");
        System.out.println("雷霆嘎巴无情哈拉少");
        response.getWriter().write("雷霆嘎巴无情哈拉少");
    }
}

运行效果

---

刚才的@WebServlet注解是3.0提出的，那么 3.0还有哪些规范

文档: https://download.oracle.com/otndocs/jcp/servlet-3.0-fr-eval-oth-JSpec/

• 一个容器在启动的时候会去找 ServletContainerInitializer 实例对象,该 实例对象 必须放在
  
  META-INF/services 目录下中一个文件名称叫 javax.servlet.ServletContainerInitializer 里面

• javax.servlet.ServletContainerInitializer

com.min.demo2.MyServletContainerInitializerTest

• 编写一个servlet

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

public class MyServletTest3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=utf-8");
        System.out.println("MyServletTest3--------------");
        response.getWriter().write("大威天龙");
    }
}

• 编写 ServletContainerInitializer 的实现类

import com.min.demo3.MyServletTest3;
import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
import java.util.Set;

public class MyServletContainerInitializerTest implements ServletContainerInitializer {
    @Override
    public void onStartup(Set<Class<?>> set, ServletContext servletContext) throws ServletException { //启动时执行
        //System.out.println("MyServletContainerInitializerTest-------------");

        //servletContext.addServlet(名称,new出来的Servlet对象);
        //servletContext.addFilter();
        //servletContext.addListener();

        //添加上自己定义的servlet
        ServletRegistration.Dynamic dynamic = servletContext.addServlet("aaa", new MyServletTest3());
        //设置启动顺序
        dynamic.setLoadOnStartup(1);
        //设置访问路径
        dynamic.addMapping("/demo3");
    }
}

• 运行效果

@HandlesTypes

@HandlesTypes(value={aaa.class}) 可以传入一个接口的字节码对象，在执行 onStartup 的时候，会把这个字节码接口对应的所有抽象类 、子接口、 实现类都获取到， 并且放在 set集合里面 保存起来

package com.min.demo2;

import com.min.demo3.MyServletTest3;
import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
import javax.servlet.annotation.HandlesTypes;
import java.util.Set;

@HandlesTypes(value = {IHello.class})  // 可以传入一个接口的字节码对象
public class MyServletContainerInitializerTest implements ServletContainerInitializer {
     // 在执行 onStartup 的时候，会把这个字节码接口对应的所有抽象类 、子接口、 实现类都获取到， 并且放在 set集合里面 保存起来
    @Override
    public void onStartup(Set<Class<?>> set, ServletContext servletContext) throws ServletException {
        //System.out.println("MyServletContainerInitializerTest-------------");

        //servletContext.addServlet(名称,new出来的Servlet对象);  添加一个servlet
        //servletContext.addFilter();  添加一个 filter
        //servletContext.addListener(); 添加一个listener

        //添加上自己定义的servlet
        ServletRegistration.Dynamic dynamic = servletContext.addServlet("aaa", new MyServletTest3());
        //设置启动顺序
        dynamic.setLoadOnStartup(1);
        //设置访问路径
        dynamic.addMapping("/demo3");
        for (Class<?> aClass : set) {
            System.out.println(aClass);
        }
    }
}

• 编写一个IHello 接口

package com.min.demo2;

public interface IHello {
}

• 编写一个子接口

package com.min.demo2;

public interface IHello_SON extends IHello {
}

• 编写一个实现类

package com.min.demo2;

public class IHello_Impl implements IHello{
}

• 编写一个抽象类

package com.min.demo2;

public abstract class IHello_Abstract implements IHello {
}

• 重启tomcat,观察打印结果