Java EE-servlet API 三种主要的类

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上述的代码如下：

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;
import java.util.Enumeration;


@WebServlet("/request")
public class RequestServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 下面这个操作也是必要的. 显式告诉浏览器, 你拿到的数据是 html.
        resp.setContentType("text/html");
        StringBuilder respBody=new StringBuilder();

        respBody.append(req.getProtocol());
        //使用 
 标签表示换行
        respBody.append("
");
        respBody.append(req.getMethod());
        respBody.append("
");
        respBody.append(req.getRequestURI());
        respBody.append("
");
        respBody.append(req.getContextPath());
        respBody.append("
");
        respBody.append(req.getQueryString());
        respBody.append("
");

        //Enumeration 枚举类型，每一个枚举类型都是一个键值对，即headers中包含多个键值对
        Enumeration<String> headers=req.getHeaderNames();
        while(headers.hasMoreElements()){//一开始的时候，并不指向第一个键值对的name
            String header= headers.nextElement();//指向第一个键值对的name
            respBody.append(header + ": "+req.getHeader(header));//getHeader:获取键值对的值
            respBody.append("
");
        }
        resp.getWriter().write(respBody.toString());
    }
}

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上述的代码如下：

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("/parameter1")
public class ParameterServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 约定, 客户端使用 query string 传递数据.
        // query string 形如: username=zhangsan&password=123
        String user_name=req.getParameter("username");
        String pass_word=req.getParameter("password");
        System.out.println("username"+":"+user_name);
        System.out.println("password"+":"+pass_word);
        resp.getWriter().write("ok");
    }
}

上述的代码如下：

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("/parameter2")
public class ParameterServlet2 extends HttpServlet {
            // 预期让客户端发送一个 POST 请求. 同时使用 form 格式的数据, 在 body 中把数据传递过来.
            // body 形如:
            // username=zhangsan&password=123
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String user_name=req.getParameter("username");
        String pass_word=req.getParameter("password");
        System.out.println("username :"+ user_name);
        System.out.println("password :"+ pass_word);
        resp.getWriter().write("okk");
    }
}

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上述过程的代码如下：

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("/status")
public class StatusServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //resp.setStatus(404);
        resp.setContentType("text/html;charset=utf8");
        resp.sendError(500);
        resp.getWriter().write("okkkk");
    }
}

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上述过程的代码如下：

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("/refresh")
public class RefreshServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //每2秒刷新一次
        resp.setHeader("refresh","2");
        resp.getWriter().write("time "+ System.currentTimeMillis());
    }
}

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上述过程的代码如下：

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("/redirect")
public class RedirectServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //resp.setStatus(302);
        //resp.setHeader("Location","http://www.baidu.com");
        resp.sendRedirect("http://www.baidu.com");
    }
}

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上述过程的代码如下：

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("/body")
public class BodyServlet extends HttpServlet {
    @Override
    //让服务器返回一个html的数据
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html;charset=utf8");
        resp.getWriter().write("
你们好呀
");
    }
}