12：Response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

```java

ServletOutputStream getOutputStream() throws IOException;

PrintWriter getWriter() throws IOException;

```

 

负责向浏览器发送响应头的方法

```java

    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

```java

    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、下载文件

1. 向浏览器输出消息 （一直在讲，就不说了）

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. 获取下载文件的输入流

   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户端！

 

```java

@Override

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

    // 1. 要获取下载文件的路径

    String realPath = "F:\\班级管理\\西开【19525】\\2、代码\\JavaWeb\\javaweb-02-servlet\\response\\target\\classes\\秦疆.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URLEncoder.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();

}

```

 

新建一个module

 

 

 

 

Web.xml

 

直接请求到后台，就可以下载了