Request and response

Request and Response summary

request： Get request data
· Browser to background server （Tomcat） send out HTTP request
·HTTP Your request will contain a lot of request data （ Request line + Request header + Request body ）
· The background server will be right HTTP Analyze the data in and store the analysis results in an object （request object ） in
· Relevant parameters can be obtained from request Object , And carry out subsequent operations
response： Set response data
· After the business is done , The background will return the result of business processing to the front end, that is, the response data
· The response data will be encapsulated in response In the object
· The server will parse response object , according to （ Response line + Response head + Response body ） Format splicing results
· The browser finally parses the result , Display the content in the browser for users to browse

Request object

Request Inheritance system

ServletRequest–>HttpServletRequest–>RequestFacade

Request Get request data

Get request line data

Get request method ：String getMethod()
Get virtual directory （ Project access path ）：String getContextPath（）
obtain URL( Uniform resource locator )：StringBuffer getRequestURL()
obtain URI( Uniform resource identifiers )：String getRequestURI()
Get request parameters (GET The way )：String getQueryString()

Get request header data

The format is key:value
So get the corresponding value according to the request header name :String getHeader(String name)

Get request body data

Browser sending GET The requested data has no request body

Get byte input stream ：ServletInputStream getInputStream()

Get character input stream （ Pure text ）：BufferedReader getReader()

BufferedReader Flow is through request Object to get , When the request is complete request The object will be destroyed ,request After the object is destroyed ,BufferedReader The flow will automatically close , So there is no need to manually close the flow here .

Get request parameters

GET The way ：String getQueryString()
POST The way ：BufferedReader getReader();

The request parameters are garbled in Chinese ：
POST：

• Analyze the causes of Chinese garbled code ：
  • POST The request parameter is through request Of getReader() To get the data in the stream
  • TOMCAT The encoding used when obtaining the stream is ISO-8859-1
  • ISO-8859-1 The code does not support Chinese , So it's going to be messy
• Solution ：
  • The coding format of page setup is UTF-8
  • hold TOMCAT The encoding before obtaining the stream data is set to UTF-8
  • adopt request.setCharacterEncoding(“UTF-8”) Set encoding ,UTF-8 It can also be written in lowercase

GET：

• GET The way to get the request parameters is request.getQueryString()
• POST The way to get the request parameters is request.getReader()
• request.setCharacterEncoding(“utf-8”) It's settings request Encoding of processing stream
• getQueryString Method does not get data through stream

Request forwarding

req.getRequestDispatcher(“ resources B route ”).forward(req,resp);

Response object

Response head
Set response status code ：void setStatus(int sc);
Set the response header key value pair ：void setHeader(String name,String value);
Get character output stream ：PrintWriter getWriter();
Get byte output stream ：ServletOutputStream getOutputStream();

request redirections （redirect）

Implementation of redirection ：
resp.setStatus(302);
resp.setHeader(“location”,“ resources B Access path of ”);
simplify ：resposne.sendRedirect(“/request-demo/resp2”)

routing problem

• Browsers use : Need to add virtual directory ( Project access path )
• Server use : No need to add virtual directory

If you pass Tomcat The plug-in configures the access path of the project , When redirecting, use getContextPath（） Method to dynamically obtain the virtual directory

Response character data

• adopt Response Object to get the character output stream ： PrintWriter writer = resp.getWriter();
• Write data through character output stream : writer.write(“aaa”);

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

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

Response byte data

• adopt Response Object to get byte output stream ：ServletOutputStream outputStream = resp.getOutputStream();
• Write data through byte output stream : outputStream.write( Bytes of data );

Return the picture to the browser

//pom rely on 
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
 </dependenct>

-------------------------------------------------
// Tool class methods 
//fis: Input stream 
//os: Output stream 
IOUtils.copy(fis,os);