线程保险箱--ThreadLocal模式

傷城~ 2023-07-19 04:51 15阅读 0赞

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<Context> 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

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2E4MEM1MQ_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2E4MEM1MQ_size_16_color_FFFFFF_t_70]: /images/20230528/1ab8604d7f28453f9ba0fa7eaab4ceb2.png