Threadlocal example

Business layer can access userId without passing the parameter from web layer.

 

 package threadlocal;  
   
 class SecurityContext {  
   
   private String userId = null;  
   
   public String getUserId() {  
     return userId;  
   }  
   
   public void setUserId(String userId) {  
     this.userId = userId;  
   }  
 }  
   
 class MyThreadLocal {  
   private static final ThreadLocal userThreadLocal = new ThreadLocal();  
   
   public static void set(SecurityContext user) {  
     userThreadLocal.set(user);  
   }  
   
   public static void unset() {  
     userThreadLocal.remove();  
   }  
   
   public static SecurityContext get() {  
     return (SecurityContext)userThreadLocal.get();  
   }  
 }  
   
 class BusinessService {  
   
   public void businessMethod() {  
     SecurityContext securityContext = MyThreadLocal.get();  
     System.out.println(securityContext.getUserId());  
   }  
 }  
   
 public class Main extends Thread{  
   public static void main(String[] args){  
     new Main().start();  
     new Main().start();  
   }  
   
   @Override  
   public void run() {  
     SecurityContext securityContext = new SecurityContext();  
     securityContext.setUserId(getName());  
     MyThreadLocal.set(securityContext);  
     new BusinessService().businessMethod();  
     MyThreadLocal.unset();  
   }  
 }  
   

Reference: http://veerasundar.com/blog/2010/11/java-thread-local-how-to-use-and-code-sample/

Effective Java Item 49: Auto boxed type NullPointerException

Seems quite innocuous, but throws NPE

Example 1

   public static void main(String[] args){  
     Boolean b = null;  
     call(b);  
   }  
   
   public static void call(boolean b){  
     System.out.println(b);  
   }  

Example 2

   public static void main(String[] args){  
     Integer i = null;  
     if (i == 42){  
       System.out.println(i);  
     }  
   }