Java Web request and Response example detailed _java

The main function of the servlet is to process the client request and respond, for each request, the Web container creates two objects before the service () is invoked, respectively, HttpServletRequest and HttpServletResponse. where HttpServletRequest encapsulates HTTP request messages, HttpServletResponse encapsulates HTTP response messages. It should be noted that each servlet creates only one instance object during the Web server run, but each request invokes the service (ServletRequest req, Servletresponse Res) method of the servlet instance. Here HttpServletRequest is a subclass of ServletRequest, HttpServletResponse is a subclass of Servletresponse.

The HttpServletRequest and HttpServletResponse interface inheritance diagrams are as follows:

1, HttpServletResponse

The HttpServletResponse interface inherits from the Servletresponse interface, because the HTTP response message is divided into the status row, the response message body, the message body three parts, A method for sending a response status code to a client, responding to a message header, and responding to a message body is defined in the HttpServletResponse interface. Although there are many methods in the HttpServletResponse interface, but we often use a few, if the other method can be read the response of the source code or related information on the line.

Send Status Code correlation function

Method	Description
public void SetStatus (int sc)	Sets the response message status code, and the Web server defaults to a status line with a status code of 200
public void Senderror (int sc)	Sends a status code that represents the error message, and the second method adds a text message for the hint description
public void Senderror (int sc, String msg)

Send Response message header correlation function

Method	Description
public void AddHeader (string name, String value)	Sets the HTTP response header field, name specifies the field name, and value specifies the field value. AddHeader can increase the response header field with the same name, SetHeader will overwrite the header field with the same name
public void SetHeader (string name, String value)
public void setcontentlength (int len)	Sets the size, in bytes, of the entity content of the response message, which sets the value of the Content-length field
public void setContentType (String type)	Sets the MIME type of the servlet output, which sets the value of the Content-type field
public void setcharacterencoding (String charset)	Set the output character encoding, that is, to set the value of the Content-type field, note that the method has a higher precedence than the setContentType
public void Sendredirect (String location)	Servlet Request Redirection

Send Response message body correlation function

Method	Description
Public Servletoutputstream Getoutputstream ()	Gets the httpservletresponse byte output stream Servletoutputstram type
Public PrintWriter getwriter ()	Gets the character output stream servletwriter type of the HttpServletResponse

Chinese output garbled problem

The data in the computer is stored in binary form, so that when the text is transferred, the conversion between the bytes of the character occurs. The conversion between characters and bytes is done through the Code table, the process of converting characters into bytes is called encoding, and the process of converting bytes to characters is called decoding, and if the Code table used for encoding and decoding is different, garbled problems will occur.

　　Note: The HttpServletResponse object's character output stream is encoded with the ISO 8859-1 encoding, which is not compatible with Chinese, for example, "China" is encoded as "63 63" (characters that are not found in the ISO 8959-1 Code table show 63). When the browser to the received data decoding, will default to use GB2312, "63" decoded to "?", the browser will "China" two characters decoded as "??".

HttpServletResponse Program Example

Package zzz;
Import java.io.IOException;
Import Java.io.PrintWriter;
Import Javax.servlet.http.HttpServlet;
Import Javax.servlet.http.HttpServletRequest;
Import Javax.servlet.http.HttpServletResponse;
public class Hello extends HttpServlet {
  @Override public
  void doget (HttpServletRequest request, HttpServletResponse response) throws IOException {
    //Set Response message encoding, after comment "China" will show "??" Garbled
    Response.setcontenttype ("Text/html;charset=utf-8");
    PrintWriter out = Response.getwriter ();
    Out.println ("Hello China");
  }
  @Override public
  void DoPost (HttpServletRequest request, httpservletresponse response) throws IOException {
    This.doget (request, response);
  }

Sometimes encountered the problem of a scheduled Jump page, http in the Refresh header field can inform the browser in a specified time to automatically refresh and jump to other pages, the Web page timed refresh and jump to the specified page.

Package zzz;
Import java.io.IOException;
Import Java.io.PrintWriter;
Import Javax.servlet.http.HttpServlet;
Import Javax.servlet.http.HttpServletRequest;
Import Javax.servlet.http.HttpServletResponse;
public class Hello extends HttpServlet {
  @Override public
  void doget (HttpServletRequest request, HttpServletResponse response) throws IOException {
    //Set Response message encoding
    response.setcontenttype ("text/html;charset= Utf-8 ");
    Response.setheader ("Refresh", "2;url=http://www.baidu.com");
    PrintWriter out = Response.getwriter ();
    Out.println ("Hello China, jump to Baidu after 2 seconds");
  }
  @Override public
  void DoPost (HttpServletRequest request, httpservletresponse response) throws IOException {
    This.doget (request, response);
  }

2, HttpServletRequest

The HttpServletRequest interface inherits the ServletRequest interface and is used specifically for marshaling HTTP request messages. Since the HTTP request information includes the request line, the request header, and the request body, the HttpServletRequest interface defines the relevant methods for obtaining the request line, the request header, and the request body.

Get the related method of the request line

Method	Description
Public String GetMethod ()	Gets the HTTP request method, POST, get, and so on
Public String Getrequesturi ()	Gets the resource name portion of the request line
Public String getquerystring ()	Gets the parameters section in the request line
Public String Getprotocol ()	Gets the protocol name and version in the request line, such as HTTP 1.1
Public String Getcontextpath ()	Gets the path that belongs to the Web application in the request URL

In fact, the method of requesting the line from the method name can see its role, here is not one of them posted.

How to get the request message headers

Method	Description
public string GetHeader (string name)	Gets the value of the specified field, if no null is returned, if multiple returns the first value
Public enumeration<string> getheaders (String name)	Returns a enumeration collection object for a specified field
Public enumeration<string> Getheadernames ()	Returns a enumeration collection object that contains all the fields
Public String getContentType ()	Get the value of the Content-type field

Print all values for the request message header field

 package zzz; import java.io.IOException; import java.io.PrintWriter; Import java.util.En
Umeration;
Import Javax.servlet.http.HttpServlet;
Import Javax.servlet.http.HttpServletRequest;
Import Javax.servlet.http.HttpServletResponse; public class Hello extends HttpServlet {@Override public void doget (HttpServletRequest request, HttpServletResponse R
    Esponse) throws IOException {//Set Response message encoding Response.setcontenttype ("Text/html;charset=utf-8");
    PrintWriter out = Response.getwriter ();
    enumeration<string> names = Request.getheadernames ();
      while (Names.hasmoreelements ()) {String name = Names.nextelement ();
      String value = Request.getheader (name);
    OUT.PRINTLN (name + ":" + value + "</br>");
    @Override public void DoPost (HttpServletRequest request, httpservletresponse response) throws IOException {
  This.doget (request, response); }
}

How to get the request body

Method	Description
Public ServletInputStream getInputStream ()	Gets the requested ServletInputStream object, if the entity content is not text, can only get the request body message body through the getInputStream method
Public BufferedReader Getreader ()	Gets the requested BufferedReader object that converts entity content byte data to a text string of the specified character set encoding

GET Request Parameters

Method	Description
public string GetParameter (string name)	Gets the specified parameter value without the parameter returning NULL
Public enumeration<string> Getparameternames ()	Returns a enumeration object that contains all the parameter names
Public string[] Getparametervalues (String name)	There may be multiple identical parameters in the HTTP request, getting all parameter values corresponding to the same parameter name

3, RequestDispatcher interface

When a Web resource is requested by a client, if you want the server to notify another resource such as processing a request, in addition to implementing redirection using functional Sendredirect (), you can also implement it through an instance object of the RequestDispatcher interface. A method--getrequestdispatcher (String path) that gets the RequestDispatcher object is defined in the ServletRequest interface. It returns the RequestDispatcher object for the resource specified by a path, and the parameter path must begin with "/" to represent the root of the current Web application, that is, the path path must be in this Web program, or an exception will occur.

Methods in RequestDispatcher interface

Method	Function
public void forward (ServletRequest request, servletresponse response)	Pass a servlet to another Web resource and pass the request to another resource for a response
public void include (ServletRequest request, servletresponse response)	Used to include other resources in the current response content

The above is a small series to introduce the Java Web request and response examples of the relevant content, I hope to help you!