线程保险箱--ThreadLocal模式

1，作用

ThreadLocal为每个线程提供了一个独立的副本。这样，线程之间的数据就相互隔离。

2，使用场景

由于和线程绑定，故在一些使用责任链模式的场景下，可以将上下文对象，放入ThreadLocal中。

3，代码示例

a）上下文对象

public class Context {

    private String name;

    private String id;

    public void setName(String name) {
        this.name = name;
    }

    public String getName(){
        return  this.name;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getId() {
        return id;
    }
}

b）核心的线程上下文

/**
 * 核心的线程上下文
 */
public class ActionContext {

    private static final ThreadLocal threadLocal = ThreadLocal.withInitial(Context::new);

    /**
     * 利用Holder模式，完成单例模式
     */
    private static class ContextHolder{
        private final static ActionContext actionContext = new ActionContext();
    }

    public static ActionContext getInstance(){
        return ContextHolder.actionContext;
    }

    public Context getContext(){
        return threadLocal.get();
    }
}

c）任务执行类

public class ExcutionTask implements Runnable {

    private QueryFromDBAction queryAction = new QueryFromDBAction();

    private QueryFromHttpAction httpAction = new QueryFromHttpAction();

    @Override
    public void run() {
        //final Context context = new Context();
        queryAction.execute();
        System.out.println("query successful");
        httpAction.execute();
        final Context context = ActionContext.getInstance().getContext();
        System.out.println("The name is "+context.getName()+"; "+context.getId());

    }
}

d）其他两个Action补充

/**
 * QueryFromDBAction
 */
public class QueryFromDBAction {

    private final Random random = new Random(System.currentTimeMillis());

    public void execute(){
        try {
            Thread.sleep(random.nextInt(1000));
            String name = "Wayne:"+Thread.currentThread().getName();
            ActionContext.getInstance().getContext().setName(name);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


/**
 * QueryFromHttpAction
 */
public class QueryFromHttpAction {

    private final Random random = new Random(System.currentTimeMillis());

    public void execute(){
        try {
            Thread.sleep(random.nextInt(1000));
            String id = "IDCard:"+Thread.currentThread().getId();
            ActionContext.getInstance().getContext().setId(id);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

e）测试类

public class ContextPatternTest {
    public static void main(String[] args) {
        IntStream.range(1,5)
                .forEach(i->{
                    new Thread(new ExcutionTask()).start();
                });
    }
}

4，测试结果