線程保險箱--ThreadLocal模式

1，作用

ThreadLocal爲每個線程提供了一個獨立的副本。這樣，線程之間的數據就相互隔離。

2，使用場景

由於和線程綁定，故在一些使用責任鏈模式的場景下，可以將上下文對象，放入ThreadLocal中。

3，代碼示例

a）上下文對象

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）核心的線程上下文

/**
 * 核心的線程上下文
 */
public class ActionContext {

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

    /**
     * 利用Holder模式，完成單例模式
     */
    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）任務執行類

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）其他兩個Action補充

/**
 * 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）測試類

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

4，測試結果