Illustrate the use of synchronized keywords in Java _java

The Synchronized keyword, as the name suggests, is used to synchronize mutually exclusive functions.

Here is a concise note of how it is used and what it means:

1. When synchronized modifies this or Non-static method or is an instance, the synchronized lock is added to this or the instance object reference. For example, A,b is an instantiated object with the main class, a invokes the Synchronized method, and B invokes the synchronized method without forming a mutex. But the method of a object invocation of different threads being synchronized is mutually exclusive.

Public synchronized void Method () { 
  //...} public 
void method () 
{ 
  synchronized (this) { 
    //... 
  } 
}

2. Unlike 1, when synchronized modifies the class name. class or Static method. Even a different object can form a mutex.

Class Main 
{public 
  synchronized static void Method1 () { 
    //...} public 
  void Method2 () { 
    Synchronized (Main.class)//  
  } 

3.eg:

Package com.asiainfolinkage.ems.web.controller.base; 
Import Java.math.BigInteger; 
Import Java.util.Date; 
Import Java.util.HashMap; 
Import Java.util.Map; 
 
Import Java.util.Random; 
Import Javax.servlet.http.HttpServletRequest; 
 
Import javax.servlet.http.HttpSession; /** * Token Controller * @version 1.0 Copyright July 29, 2013 PM 3:38:30 * * Public abstract class Tokenbasecontroller extend 
 
  s Basecontroller {private static map<string, string> Springmvc_token = new hashmap<string, string> (); 
    /** generates a unique value of token */public String Generateguid (HttpSession session) {String token = ""; 
    Date date = new Date (); 
        Synchronized (Springmvc_token) {try {Object obj = Session.getattribute (constants.spring_mvc_tokenname); if (obj!= null) Springmvc_token = (map<string, string>) Session.getattribute (constants.spring_m 
        Vc_tokenname); 
    token = new BigInteger (165, New Random ()). ToString (). toUpperCase ();    Springmvc_token.put (Constants.default_token_name + "." + token, token); 
        Session.setattribute (Constants.spring_mvc_tokenname, Springmvc_token); 
      Constants.token_value = TOKEN; 
      catch (IllegalStateException e) {_log.error ("generateguid () Mothod Find Bug,by session ..."); 
  } return token; /** Verify that the token value of the form and the token value in the session are consistent */public boolean validtoken (HttpServletRequest request) {String Inputt 
 
    Oken = Getinputtoken (request); 
      if (Inputtoken = = null) {_log.warn ("token is isn't valid!inputtoken is null"); 
    return false; 
    HttpSession session = Request.getsession (); map<string, string> Tokenmap = (map<string, string>) Session.getattribute (constants.spring_mvc_tokenname 
    ); 
      if (Tokenmap = null | | tokenmap.size () < 1) {_log.warn ("token is isn't valid!sessiontoken is null"); 
    return false; String Sessiontoken = Tokenmap.get (constants.default_Token_name + "." + Inputtoken); if (!inputtoken.equals (Sessiontoken)) {_log.warn ("token is not valid!inputtoken= '" + Inputtoken + "", Sessiontoken 
      = ' "+ Sessiontoken +" ' "); 
    return false; 
    } tokenmap.remove (Constants.default_token_name + "." + Inputtoken); 
 
    Session.setattribute (Constants.spring_mvc_tokenname, Tokenmap); 
  return true; /** get the token value in the form/private String Getinputtoken (HttpServletRequest request) {Map params = Request.getparam 
    Etermap (); 
      if (!params.containskey (Constants.default_token_name)) {_log.warn ("could not find TOKEN NAME in params."); 
    return null; 
    } string[] tokens = (string[]) (string[]) params.get (constants.default_token_name); if ((tokens = null) | | (Tokens.length < 1)) 
      {_log.warn ("Got a null or empty token name."); 
    return null; 
  return tokens[0];  } 
}