Response object - response character data

Response The response data

1. response Return the character data to the browser

Two steps are needed. ：

1. adopt response Object to get the character output stream PrintWriter writer = resp.getWriter();
2. Write data through character output stream ：writer.writer(“aaa”);
   Case study
   Print out characters in browser

/** *  Response character data ： Set the response body of character data  */
@WebServlet("/resp3")
public class ResponseDemo3 extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        response.setContentType("text/html;charset=utf-8");
        //1.  Get character output stream 
        PrintWriter writer = response.getWriter();
		 writer.write("aaa");
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        this.doGet(request, response);
    }
}

You can go back to html character string , And the browser can parse it , as follows ：

PrintWriter writer = response.getWriter();
//content-type, Tell the browser what type of data to return HTML Type data , In this way, the browser will parse HTML label 
response.setHeader("content-type","text/html");
writer.write("<h1>aaa</h1>");

Be careful ： After a request response ,response The object will be destroyed , So don't close the flow manually

remind If you want to return a Chinese string Hello , You need to set the response data code to utf-8

// Set the data format and code of the response 
response.setContentType("text/html;charset=utf-8");
writer.write(" Hello ");

2. response Response byte data

You need to write byte data back to the browser , We need two steps ：

• adopt response Object to get byte output stream ：servletOutputStream outputStream = resp.getOutputStream();
• Write data through byte output stream ：outputStream.write( Bytes of data );
  1. Returns a picture file to the browser , as follows ：

/** *  Response byte data ： Set the response body of byte data  */
@WebServlet("/resp4")
public class ResponseDemo4 extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        //1.  Read the file 
        FileInputStream fis = new FileInputStream("d://a.jpg");
        //2.  obtain response Byte output stream 
        ServletOutputStream os = response.getOutputStream();
        //3.  Completion flow copy
        byte[] buff = new byte[1024];
        int len = 0;
        while ((len = fis.read(buff))!= -1){
    
            os.write(buff,0,len);
        }
        fis.close();
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        this.doGet(request, response);
    }
}

In the above code , For flow copy The code is more complex , So we can use good methods provided by others to simplify code development , The specific steps are as follows ：

1. pom.xml Add dependency

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>

2. Call tool class method

//fis: Input stream 
//os: Output stream 
IOUtils.copy(fis,os);

After optimizing the code ：

/** *  Response byte data ： Set the response body of byte data  */
@WebServlet("/resp4")
public class ResponseDemo4 extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        //1.  Read the file 
        FileInputStream fis = new FileInputStream("d://a.jpg");
        //2.  obtain response Byte output stream 
        ServletOutputStream os = response.getOutputStream();
        //3.  Completion flow copy
      	IOUtils.copy(fis,os);
        fis.close();
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        this.doGet(request, response);
    }
}

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