JavaWeb基础学习6

JavaWeb基础

HttpServletResponse

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

• 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

简单分类

负责向浏览器发送数据的方法

 public ServletOutputStream getOutputStream() throws IOException;
 public PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

 public void setCharacterEncoding(String charset);
 public void setContentLength(int len);
 public void setContentLengthLong(long len);
 public void setContentType(String type);
 public void setBufferSize(int size);

default public Supplier<Map<String, String>> getTrailerFields() {
        return null;
    }

    /*
     * Server status codes; see RFC 2068.
     */

    /**
     * Status code (100) indicating the client can continue.
     */
    public static final int SC_CONTINUE = 100;

    /**
     * Status code (101) indicating the server is switching protocols according to Upgrade header.
     */
    public static final int SC_SWITCHING_PROTOCOLS = 101;

    /**
     * Status code (200) indicating the request succeeded normally.
     */
    public static final int SC_OK = 200;

    /**
     * Status code (201) indicating the request succeeded and created a new resource on the server.
     */
    public static final int SC_CREATED = 201;

    /**
     * Status code (202) indicating that a request was accepted for processing, but was not completed.
     */
    public static final int SC_ACCEPTED = 202;

    /**
     * Status code (203) indicating that the meta information presented by the client did not originate from the server.
     */
    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;

    /**
     * Status code (204) indicating that the request succeeded but that there was no new information to return.
     */
    public static final int SC_NO_CONTENT = 204;

    /**
     * Status code (205) indicating that the agent SHOULD reset the document view which caused the request to be
     * sent.
     */
    public static final int SC_RESET_CONTENT = 205;

    /**
     * Status code (206) indicating that the server has fulfilled the partial GET request for the resource.
     */
    public static final int SC_PARTIAL_CONTENT = 206;

    /**
     * Status code (300) indicating that the requested resource corresponds to any one of a set of representations, each
     * with its own specific location.
     */
    public static final int SC_MULTIPLE_CHOICES = 300;

    /**
     * Status code (301) indicating that the resource has permanently moved to a new location, and that future references
     * should use a new URI with their requests.
     */
    public static final int SC_MOVED_PERMANENTLY = 301;

    /**
     * Status code (302) indicating that the resource has temporarily moved to another location, but that future references
     * should still use the original URI to access the resource.
     *
     * This definition is being retained for backwards compatibility. SC_FOUND is now the preferred definition.
     */
    public static final int SC_MOVED_TEMPORARILY = 302;

    /**
     * Status code (302) indicating that the resource reside temporarily under a different URI. Since the redirection might
     * be altered on occasion, the client should continue to use the Request-URI for future requests.(HTTP/1.1) To represent
     * the status code (302), it is recommended to use this variable.
     */
    public static final int SC_FOUND = 302;

    /**
     * Status code (303) indicating that the response to the request can be found under a different URI.
     */
    public static final int SC_SEE_OTHER = 303;

    /**
     * Status code (304) indicating that a conditional GET operation found that the resource was available and not modified.
     */
    public static final int SC_NOT_MODIFIED = 304;

    /**
     * Status code (305) indicating that the requested resource MUST be accessed through the proxy given by the
     * Location field.
     */
    public static final int SC_USE_PROXY = 305;

    /**
     * Status code (307) indicating that the requested resource resides temporarily under a different URI. The temporary URI
     * SHOULD be given by the Location field in the response.
     */
    public static final int SC_TEMPORARY_REDIRECT = 307;

    /**
     * Status code (400) indicating the request sent by the client was syntactically incorrect.
     */
    public static final int SC_BAD_REQUEST = 400;

    /**
     * Status code (401) indicating that the request requires HTTP authentication.
     */
    public static final int SC_UNAUTHORIZED = 401;

    /**
     * Status code (402) reserved for future use.
     */
    public static final int SC_PAYMENT_REQUIRED = 402;

    /**
     * Status code (403) indicating the server understood the request but refused to fulfill it.
     */
    public static final int SC_FORBIDDEN = 403;

    /**
     * Status code (404) indicating that the requested resource is not available.
     */
    public static final int SC_NOT_FOUND = 404;

    /**
     * Status code (405) indicating that the method specified in the Request-Line is not allowed for
     * the resource identified by the Request-URI.
     */
    public static final int SC_METHOD_NOT_ALLOWED = 405;

    /**
     * Status code (406) indicating that the resource identified by the request is only capable of generating response
     * entities which have content characteristics not acceptable according to the accept headers sent in the request.
     */
    public static final int SC_NOT_ACCEPTABLE = 406;

    /**
     * Status code (407) indicating that the client MUST first authenticate itself with the proxy.
     */
    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;

    /**
     * Status code (408) indicating that the client did not produce a request within the time that the server was prepared
     * to wait.
     */
    public static final int SC_REQUEST_TIMEOUT = 408;

    /**
     * Status code (409) indicating that the request could not be completed due to a conflict with the current state of the
     * resource.
     */
    public static final int SC_CONFLICT = 409;

    /**
     * Status code (410) indicating that the resource is no longer available at the server and no forwarding address is
     * known. This condition SHOULD be considered permanent.
     */
    public static final int SC_GONE = 410;

    /**
     * Status code (411) indicating that the request cannot be handled without a defined
     * Content-Length.
     */
    public static final int SC_LENGTH_REQUIRED = 411;

    /**
     * Status code (412) indicating that the precondition given in one or more of the request-header fields evaluated to
     * false when it was tested on the server.
     */
    public static final int SC_PRECONDITION_FAILED = 412;

    /**
     * Status code (413) indicating that the server is refusing to process the request because the request entity is larger
     * than the server is willing or able to process.
     */
    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;

    /**
     * Status code (414) indicating that the server is refusing to service the request because the
     * Request-URI is longer than the server is willing to interpret.
     */
    public static final int SC_REQUEST_URI_TOO_LONG = 414;

    /**
     * Status code (415) indicating that the server is refusing to service the request because the entity of the request is
     * in a format not supported by the requested resource for the requested method.
     */
    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;

    /**
     * Status code (416) indicating that the server cannot serve the requested byte range.
     */
    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;

    /**
     * Status code (417) indicating that the server could not meet the expectation given in the Expect request header.
     */
    public static final int SC_EXPECTATION_FAILED = 417;

    /**
     * Status code (500) indicating an error inside the HTTP server which prevented it from fulfilling the request.
     */
    public static final int SC_INTERNAL_SERVER_ERROR = 500;

    /**
     * Status code (501) indicating the HTTP server does not support the functionality needed to fulfill the request.
     */
    public static final int SC_NOT_IMPLEMENTED = 501;

    /**
     * Status code (502) indicating that the HTTP server received an invalid response from a server it consulted when acting
     * as a proxy or gateway.
     */
    public static final int SC_BAD_GATEWAY = 502;

    /**
     * Status code (503) indicating that the HTTP server is temporarily overloaded, and unable to handle the request.
     */
    public static final int SC_SERVICE_UNAVAILABLE = 503;

    /**
     * Status code (504) indicating that the server did not receive a timely response from the upstream server while acting
     * as a gateway or proxy.
     */
    public static final int SC_GATEWAY_TIMEOUT = 504;

    /**
     * Status code (505) indicating that the server does not support or refuses to support the HTTP protocol version that
     * was used in the request message.
     */
    public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
}

常见应用

1. 向浏览器输出信息

2. 下载文件

3. 验证码功能

4. 实现重定向

下载文件

• 要获取下载文件的路径
• 下载的文件名
• 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

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//		 要获取下载文件的路径
//  String rp = this.getServletContext().getRealPath("/15196900621605176.jpg");
    String rp = "C:\\Users\\HAI\\Desktop/15196900621605176.jpg";
//		 下载的文件名
		String fileName = rp.substring(rp.lastIndexOf("\\")+1);
//		 设置想办法让浏览器能够支持下载我们需要的东西,中文文件用URLEncoder.encode(fileName,"UTF-8")编码，否则可能会乱码
		response.setHeader("Content-disposition","attachment;filename="+fileName);
//		 获取下载文件的输入流
		FileInputStream in = new FileInputStream(rp);
//		 创建缓冲区
		int len = 0;
		byte[] buffer = new byte[1024];
//		 获取OutputStream对象
		ServletOutputStream outputStream = response.getOutputStream();
//		 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) {
			outputStream.write(buffer, 0, len);
		}
		in.close();
		outputStream.close();
	}

测试结果：

验证码功能

验证怎么来的？

1. 前端实现
2. 后端实现，需要用到Java的图片类，生成一个图片

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//如何让浏览器3秒自动刷新一次
		response.setHeader("refresh","5");
		//在内存中创建一个图片
		BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
		//得到图片
		Graphics2D g = (Graphics2D) image.getGraphics();
		
		//设置图片的背景颜色
		g.setColor(Color.white);
		g.fillRect(0, 0, 80, 20);
		//给图片写数据
		g.setColor(Color.blue);
		g.setFont(new Font(null,Font.BOLD,20));
		g.drawString(makeNum(),0,20);
		//告诉浏览器这个请求用图片的方式打开
		response.setContentType("image/jpeg");
		//网站存在缓存，不让它缓存
		response.setContentType("expires");
		response.setHeader("Cache-Control","no-cache");
		response.setHeader("Pragma","no-cache");
		//把图片给浏览器
		ImageIO.write(image, "jpg",response.getOutputStream());
	}

	
	private String makeNum() {   //生成随机数
		Random random = new Random();
		String num = random.nextInt(9999999)+ "";
		StringBuffer sb = new StringBuffer();
		//保证7位数随机数
		for (int i=0;i<7-num.length();i++) {
			sb.append("0");
		}
		num = sb.toString()+ num;
		return num;
	}

测试结果：

实现重定向

一个web资源收到客户端请求后会告诉客户端去访问另一个web资源，通过另一个资源访问

response.sendRedirect("/jjj/yanzheng");
//结果会跳转到yanzheng这个界面
//原理：
//response.setHeader("Location", "/jjj/yanzheng");
//response.setStatus(302);

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：

  1. 请求转发的时候 URL不会发生变化
  2. 重定向时，URL地址栏会发生变化