java 设置响应头注解 java请求和响应

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jojo 2023-08-30 14:31:00

文章标签 java 设置响应头注解 java 客户端 Image 文章分类 Java 后端开发

JavaWeb之客户端请求和响应

1.HttpServletResponse

1.1简单分类

2.HttpServletRequest

1.HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse；

如果要获取客户端请求过来的参数:找HttpServletRequest
如果要给客户端响应一些信息：找HttpServletResponse

1.1简单分类

负责向浏览器发送数据的方法

ServletoutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

void setCharacteEncoding(String var1);
void setContentLength(int var1);
void setContenLengthLong(long var1);
void setContenType(String var1);
void addDateHeader(String var1,String var2);
void setHeader(String var1,)

响应的状态码

int SC_CONTINUE = 100;
    int SC_SWITCHING_PROTOCOLS = 101;
    int SC_OK = 200;
    int SC_CREATED = 201;
    int SC_ACCEPTED = 202;
    int SC_NON_AUTHORITATIVE_INFORMATION = 203;
    int SC_NO_CONTENT = 204;
    int SC_RESET_CONTENT = 205;
    int SC_PARTIAL_CONTENT = 206;
    int SC_MULTIPLE_CHOICES = 300;
    int SC_MOVED_PERMANENTLY = 301;
    int SC_MOVED_TEMPORARILY = 302;
    int SC_FOUND = 302;
    int SC_SEE_OTHER = 303;
    int SC_NOT_MODIFIED = 304;
    int SC_USE_PROXY = 305;
    int SC_TEMPORARY_REDIRECT = 307;
    int SC_BAD_REQUEST = 400;
    int SC_UNAUTHORIZED = 401;
    int SC_PAYMENT_REQUIRED = 402;
    int SC_FORBIDDEN = 403;
    int SC_NOT_FOUND = 404;
    int SC_METHOD_NOT_ALLOWED = 405;
    int SC_NOT_ACCEPTABLE = 406;
    int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
    int SC_REQUEST_TIMEOUT = 408;
    int SC_CONFLICT = 409;
    int SC_GONE = 410;
    int SC_LENGTH_REQUIRED = 411;
    int SC_PRECONDITION_FAILED = 412;
    int SC_REQUEST_ENTITY_TOO_LARGE = 413;
    int SC_REQUEST_URI_TOO_LONG = 414;
    int SC_UNSUPPORTED_MEDIA_TYPE = 415;
    int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
    int SC_EXPECTATION_FAILED = 417;
    int SC_INTERNAL_SERVER_ERROR = 500;
    int SC_NOT_IMPLEMENTED = 501;
    int SC_BAD_GATEWAY = 502;
    int SC_SERVICE_UNAVAILABLE = 503;
    int SC_GATEWAY_TIMEOUT = 504;
    int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2.常见应用

向浏览器输出消息
下载文件

要获取下载文件的路径
下载的文件名是啥？
设置想办法让浏览器能够支持下载我们需要的东西
获取下载文件的输入流
创建缓冲区
获取OutputStream对象
将FileOutputStream流写入到buffer缓冲区
使用OutputStream将缓冲区中的数据输出到客户端！

@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

		String realPath="C:\\Users\\DELL\\Desktop\\GitResp\\javaweb-01-maven\\response\\target\\classes\\1.png";
		//  1.要获取下载文件的路径
//		String realPath = this.getServletContext().getRealPath("/1.png");
		System.out.println("下载文件的路径："+realPath);
//	2.下载的文件名是啥？
		String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
//  3.设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncode.encode编码，否则有可能乱码
		resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
//	4.获取下载文件的输入流
		FileInputStream in= new FileInputStream(realPath);
//	5.创建缓冲区
		int len=0;
	byte[] buffer=new byte[1024];
//	6.获取OutputStream对象
		ServletOutputStream out= resp.getOutputStream();
//	7.将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端！
		while ((len=in.read(buffer))>0){
			out.write(buffer,0,len);

		}
		in.close();
		out.close();
	}

3.验证码功能
验证怎么来的?
- 前端实现
- 后端实现，需要用到java的图片类，生成一个图片

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次；
        resp.setHeader("refresh","3");
//        在内存中创建一个图片,指定宽高、图像字节灰度
        BufferedImage Image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics =(Graphics2D) Image.getGraphics();//笔
        //设置图片的背景颜色
        graphics.setColor(Color.white);
        graphics.fillRect(0,0,80,20);
        //给图片写数据
        graphics.setColor(Color.blue);
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.drawString(makeNum(),0,20);
        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","ni-cache");
        ImageIO.write(Image,"jpg",resp.getOutputStream());
    }
//生成随机数
    private String makeNum(){
        Random random = new Random();
       String num=random.nextInt(9999999)+"";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7-num.length(); i++) {
            sb.append("0");
        }
      num=sb.toString()+num;
        return num;
    }

实现重定向

一个web资源收到客户端请求后，他会通知客户端去访问另外一个web资源，这个过程叫重定向
常见场景：

用户登录

void sendRedirect(String var1) throws IOException;

测试：

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.setHeader("Location","/r/img");
//        resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
        resp.sendRedirect("/Image");//重定向
    }

面试题：请你聊聊重定向和转发的区别？
相同点：

页面都会实现跳转
不同点
请求转发的时候，url不会产生变化 307
重定向时候，url地址栏会发送变化；302

index.jsp

<html>
	<body>
		<h2>Hel1o World!</h2>
		
		《%--这里超交的路径,需要寻找到项目的路径--%>
		<%--${pageContext. request, contextPath}代表当前的项目--%>
		<form action="${pageContext. request.contextPath}/login" method="get">
			用户名: <input type="text" name="username"> <br>
			密码: <input type="password" name="password"> <br>
			<input type="submit">
		</form>
	
	</body>
</html>

RequestTest.java

public class RequestTest extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //处理方求
    String username = req.getParameter( s: "username");
    String password  rea.getParameter( s: "password");

    System.out.println(username+":"+password);

    resp.sendRedirect(s: "/r/success.jsp");
}

重定向页面success.jsp

<%@ page contentType="text/html; charset=UTF-8" language="java" %>
<html>
    <head>
	    <title>Title</title>
	    </head>
    <body>
    	<h1>success</h1>
    </body>
</html>

web.xml配置

<servlet>
    <servlet-name>requset</servlet-name>
    <servlet-class>com. kuang. servlet. RequestTest</servlet-class>
    </servlet>
    <servlet-mapping>
    <servlet-name>requset</servlet-name>
    <url-pattern>/login</url-pattern>
    </servlet-mapping>

导入依赖的jar包

<dependencies>
    <!-- https://mvnrepository. com/artifact/javax. servLet/javax. servlet-opi -->
    <dependency>
    <groupld>javax.servlet</grouptd>
    <artifactId>javax. servlet-api</artifactId>
    <version>4.0.1</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/javax. servLet.jsp/javax. servLet.jsp-opi -->
    <dependency>
    <groupId>javax.servlet.jsp</groupld>
    <artifactId>javax. servlet.jsp-api</artifactId>
    <version>2.3.3</version>
    </dependency>
    </dependencies>
    </project>

2.HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过这个HttpServletRequest的方法，获得客户端的所有信息；

java 设置响应头注解 java请求和响应_Image

1.获取参数，请求转发

java 设置响应头注解 java请求和响应_客户端_02

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbys= req.getParameterValues("hobbys");
        System.out.println("=================");
        //后台接收中文乱码问题
        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbys));
        System.out.println("=============");
        //通过请求转发
        //这里的 / 代表当前的web应用
        req.getRequestDispatcher("/success.jsp").forward(req,resp);

java 设置响应头注解 java请求和响应_java 设置响应头注解_03