狂神说 javaweb 12集：Reponse 下载文件

12,Reponse 下载文件

6.6 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.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 setCharacterEncoding(String var1);
 ​
 void setContentLength(int var1);
 ​
 void setContentLengthLong(long var1);
 ​
 void setContentType(String var1);
 ​
 void setDateHeader(String var1, long var2);
 ​
 void addDateHeader(String var1, long var2);
 ​
 void setHeader(String var1, String var2);
 ​
 void addHeader(String var1, String var2);
 ​
 void setIntHeader(String var1, int var2);
 ​
 void addIntHeader(String var1, int var2);
 ​

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

1. 向浏览器输出消息

2. 下载文件

   1. 要获取下载文件的路径

   2. 下载的文件名是啥

   3. 设置想办法让浏览器能够支持下载我们需要的东西

   4. 获取下载文件的输出流

   5. 创建缓冲区

   6. 获取OutputStream对象

   7. 将FileOutputStream流写入到buffer缓冲区

   8. 使用OutputStream将缓冲区中的数据输出到客服端！

   java文件下载案例

    public class FlieServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            // 1. 要获取下载文件的路径
            String realPath = "C:\\Users\\chene\\IdeaProjects\\javaweb-02-servlet\\response\\target\\classes\\1.jpg";
            System.out.println(realPath);
    ​
            // 2. 下载的文件名是啥(重要技巧)
            String fileName = realPath.substring( realPath.lastIndexOf( "\\" ) + 1 );
            // 3. 设置想办法让浏览器能够支持下载我们需要的东西
            resp.setHeader("Content-disposition","attachment;filename=" + URLEncoder.encode(fileName,"utf-8"));
    ​
            // 4. 获取下载文件的输出流
            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服端！
            while ((len =in.read(buffer)) >0){
                out.write( buffer, 0,len);
            }
            out.close();
            in.close();
        }
    ​
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet( req, resp );
        }
    }

3.