servlet(二）-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_45860824/article/details/121625328

本文详细介绍了如何在Servlet中操作客户端请求头（如GET、POST表单提交）和服务器响应头，包括获取HTTP方法、字符编码、URL、MIME类型，以及设置状态码、刷新页面和重定向。涵盖了HTTP状态码列表和常用操作示例。

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servlet

Servlet 客户端 HTTP 请求
Servlet 服务器 HTTP 响应
Http状态码

Servlet 客户端 HTTP 请求

客户端Request常见报头

当浏览器请求网页时，它会向 Web 服务器发送特定信息，这些信息不能被直接读取，因为这些信息
是作为 HTTP 请求的头的一部分进行传输的。
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操作 HTTP Request头的方法

下面的方法可用在 Servlet 程序中读取 HTTP 头。这些方法通过 HttpServletRequest 对象使用：
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举例

核心方法使用1-基本方法使用：

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.io.PrintWriter;
@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
        response.setContentType("text/html");

        PrintWriter out = response.getWriter();
        String method = request.getMethod();//返回请求的 HTTP 方法的名称
        String encoding = request.getCharacterEncoding();//返回请求主体中使用的字符编 码的名称
        String url = request.getContextPath();//返回指示请求上下文的请求 URI 部分
        String contentType = request.getContentType();//返回请求主体的 MIME 类型，如 果不知道类型则返回 null
        String title = "HTTP Function Test!";
        String docType = "<!doctype html>\n";
        out.println(docType + "<html>\n" +
                "<head><title>" +title+ "</title></head>\n" +
                "<body>"+
                "<h3> Method: " +method+ "</h3>" +
                "<h3> encoding: " +encoding+ "</h3>" +
                "<h3> url: " +url+ "</h3>" +
                "<h3> contentType: " +contentType+ "</h3>" +
                "</body>"+
                "</html>");
        System.out.println("访问");
    }
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);
        System.out.println("da访问");
    }
}

访问结果
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核心方法使用2-表单

先编写我们基本的index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="index" method="GET">
    <!--先使用GET-->
    first_name:<input type="text" name="first_name">
    <br />
    last_name:<input type="text" name="last_name" />
    <input type="submit" value="submit" />
</form>
</body>
</html>

编写处理Servlet逻辑

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.io.PrintWriter;
@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
        response.setContentType("text/html");

        PrintWriter out = response.getWriter();
        String method = request.getMethod();//返回请求的 HTTP 方法的名称

        String first_name = request.getParameter("first_name");
        String last_name = request.getParameter("last_name");
        String title = "HTTP Function Test!";
        String docType = "<!doctype html>\n";
        out.println(docType + "<html>\n" +
                "<head><title>" +
                title+
                "</title></head>\n" +
                "<body>"+ "<h3> method: " +method+
                "</h3>" +
                "<h3> first_name: " +
                first_name+ "</h3>" +
                "<h3> last_name: " +last_name+
                "</h3>" + "</body>"+ "</html>");
    }
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);
        System.out.println("da访问");
    }
}

验证结果
先填写参数

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改成POST请求,修改index.html

结果，可以说明post请求比get请求更私密了，正文传参没有返回到url中。

核心方法使用3-获取HTTP Request头部信息

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.io.PrintWriter;
import java.util.Enumeration;

@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        response.setContentType("text/html");

        PrintWriter out = response.getWriter();

        String title = "HTTP Header Request";
        String docType = "<!doctype html\">\n";
        out.println(docType + "<html>\n" +
                "<head><title>" + title +
                "</title></head>\n" +
                "<body>\n" + "<h1 align=\"center\">" + title +
                "</h1>\n" +
                "<table width=\"100%\" border=\"2\" align=\"center\">\n" + "<tr>\n" +
                "<th>Header name</th><th>Header value</th>\n" +
                "</tr>\n");
        Enumeration headerNames = request.getHeaderNames();//返回一个枚举，包含在该请 求中包含的所有的头名。
        while (headerNames.hasMoreElements()) {
            String paramName = (String) headerNames.nextElement();
            out.print("<tr><td>" + paramName + "</td>\n");
            String paramValue = request.getHeader(paramName);//以字符串形式返回指定 的请求头的值
            out.println("<td> " + paramValue + "</td></tr>\n");
        }
        out.println("</table>\n</body></html>");
    }

        

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);
        System.out.println("da访问");
    }
}

结果
在这里插入图片描述

Servlet 服务器 HTTP 响应

服务器端Response常见报头

在这里插入图片描述

操作HTTP Response头的方法

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举例：

核心方法使用-自动刷新页面

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.io.PrintWriter;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.GregorianCalendar;

@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        // 设置刷新自动加载时间为 1 秒
        response.setIntHeader("Refresh", 1);
        // 设置一个带有给定的名称和整数值的响应报 头。
        // 设置响应内容类型
        response.setContentType("text/html");
        // Get current time
        Calendar calendar = new GregorianCalendar();//获取当前系统时间
        String am_pm;
        int hour = calendar.get(Calendar.HOUR);//获得时
        int minute = calendar.get(Calendar.MINUTE);// 获得分
        int second = calendar.get(Calendar.SECOND);//获得秒
        if (calendar.get(Calendar.AM_PM) == 0) //判定是否是上午和下午
            am_pm = "AM";
        else
            am_pm = "PM";
        String CT = hour + ":" + minute + ":" + second + " " + am_pm;
        PrintWriter out = response.getWriter();
        String title = "auto refresh Header set";
        String docType = "<!doctype html>\n";
        out.println(docType +
                "<html>\n" +
                "<head><title>" + title +
                "</title></head>\n" +
                "<body>\n" +
                "<h1 align=\"center\">" +
                title + "</h1>\n" +
                "<p>current time: " + CT +
                "</p>\n");

    }
    // 处理 POST 方法请求的方法
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);

    }
}

结果
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Http状态码

HTTP 状态码列表

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设置 HTTP 状态代码的方法

下面的方法可用于在 Servlet 程序中设置 HTTP 状态码。这些方法通过 HttpServletResponse 对象可用。
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代码示例

核心方法1-返回404错误

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.io.PrintWriter;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.GregorianCalendar;

@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        // 设置错误代码和原因
        response.sendError(404, "Not Found!!!" );

    }
    // 处理 POST 方法请求的方法
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);

    }
}

在这里插入图片描述
核心方法2-重定向

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.io.PrintWriter;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.GregorianCalendar;

@WebServlet("/index")
public class HelloServlet extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        // 设置错误代码和原因
        response.sendRedirect("https://www.baidu.com");

    }
    // 处理 POST 方法请求的方法
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{
        doGet(request,response);

    }
}