Question

当我在Android系统上使用SimpleDateFormat时，我发现了这一点错误。 100个线程运行simpleDateFormat.format（new 日期（System.currentTimeMillis）），大约30秒后，它会响应错误的结果，是他们的任何人告诉我为什么。顺便说一下，在Jdk上运行的相同代码没有找到这个问题。

Below is my code

Utils.java

public class Utils {
public static SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
public static BlockingQueue<String> msgQueue = new ArrayBlockingQueue<String>(100);

}

DateTimeRun.java

public class DateTimeRun implements Runnable {
private boolean running = true;
SimpleDateFormat simpleDateFormat = null;
BlockingQueue<String> queue;
public DateTimeRun(SimpleDateFormat sdf, BlockingQueue<String> queue){
    this.simpleDateFormat = sdf;
    this.queue = queue;
}
public void StopRunning(){
    this.running = false;
}

@Override
public void run() {
    while (this.running){
        Date d = new Date(System.currentTimeMillis());
        String msg = simpleDateFormat.format(d);
        if(msg.length()!=14){
            try {
                queue.put(msg);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

}

MainActivity.java

public class MainActivity extends AppCompatActivity {
public TextView textView = null;//(TextView)findViewById(R.id.txt_view);
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    initTask();
}

private void initTask(){
    textView = (TextView)findViewById(R.id.txt_view);
    Button button = (Button)findViewById(R.id.btn_Start);
    final Handler handler = new Handler(){
        public void handleMessage(Message msg){
            switch (msg.what){
                case 1:
                    Bundle bundle = msg.getData();
                    String m = bundle.getString("datetimemsg");
                    m = String.format("%s\n%s",m,MainActivity.this.textView.getText().toString());
                    MainActivity.this.textView.setText(m);
                    break;
            }
            super.handleMessage(msg);
        }
    };

    button.setOnClickListener(new View.OnClickListener(){

        @Override
        public void onClick(View view) {
            //textView.setText("aaaa");
            final List<DateTimeRun> runList = new ArrayList<DateTimeRun>();
            for(int i=0;i<100;i++) {
                runList.add(new DateTimeRun(Utils.simpleDateFormat, Utils.msgQueue));
            }
            for(DateTimeRun dtr:runList){
                Thread t = new Thread(dtr);
                t.start();
            }

            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() {
                    int times = 10;
                    while(times>0){
                        try {
                            times--;
                            String msg = Utils.msgQueue.take();
                            Message message = new Message();
                            message.what = 1;
                            Bundle data = new Bundle();
                            data.putString("datetimemsg",msg);
                            message.setData(data);
                            handler.sendMessage(message);
                            System.out.println(msg);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }

                    for(DateTimeRun t: runList){
                        t.StopRunning();
                    }
                }
            });
            thread.start();
        }
    });
}

这是系统输出结果：

I / System.out:2016121816400002

I / System.out:2016120018164003

I / System.out:2016121816004003

I / System.out:2016001218164004

I / System.out:2016121816400004

I / System.out:2016121800164005

I / System.out:2016120018164005

I / System.out:2016121816004006

I / System.out:2016120018164007

I / System.out:2016001218164009

这是剪切图像： the result of formated datetime length is not 14

Answer 1

SimpleDateFormat 不线程安全。

无法创建单个实例并在线程间重复使用，而是在需要时创建新的SimpleDateFormat。

请参阅：https://stackoverflow.com/a/6840856/819355

Android SimpleDateFormat.format的方法可能会给出错误结果

1 个答案: