在實際項目中,通常有這樣的要求,對於同一個線程內多次請求獲取對象,對象要求必須爲同一個(如數據多表庫多表進行事務處理,請求的連接對象必須爲同一個),這就要用到線程管理技術。
線程管理,涉及到一個核心的類,java.lang.ThreadLocal,通過這個類來僅實現相應的功能。
代碼演示:
public class ThreadLocalDemo {
private static ThreadLocal<Object> t1 = new ThreadLocal<Object>();
public static Object getValue(){
Object o = t1.get();//不用給key,因爲t1內部會自動獲取當前線程的thread對象,並以上作爲key到它的池中去
取obj
if(o==null){
System.out.println("空的....");
Random r = new Random();
o = r.nextInt(1000);
t1.set(o);
}
return o;
}
@Test
public void test(){
Object obj = getValue();
Object obj2 = getValue();
System.out.println(obj+","+obj2);
System.out.println(obj==obj2); //true
A a = new A();
Object obj3 = a.aa();
System.out.println(obj==obj3); //true
B b = new B();
Object obj4 = b.bb();
System.out.println(obj3==obj4); //true
System.out.println("=================");
new Thread(){
@Override
public void run() {
A a = new A();
Object obj5 = a.aa();
System.out.println("obj5:"+obj5);
B b = new B();
Object obj6 = b.bb();
System.out.println("obj6:"+obj6);
System.out.println(obj5==obj6); //true
}
}.start();
}
}
class A{
public Object aa(){
Object obj3 = ThreadLocalDemo.getValue();
System.out.println(obj3);
return obj3;
}
}
class B{
public Object bb(){
Object obj4 = ThreadLocalDemo.getValue();
System.out.println(obj4);
return obj4;
}
}
仿ThreadLocal功能:
public class MyThreadLocal {
private Map<Thread,Object>map = new HashMap<Thread,Object>();
public Object get(){
Thread currentThread = Thread.currentThread();
Object obj = map.get(currentThread);
return obj;
}
public void set(Object obj){
Thread currentThread = Thread.currentThread();
map.put(currentThread,obj);
}
}