Using the service business class in the Java multi-threaded run method will cause a java.lang.NullPointerException exception. This is due to the business class injected by spring. is null, or the direct new business object is also null.
Multi-threading will prevent injection for thread safety. Therefore, when you want to use the service business class, you need to use the ApplicationContext method to obtain the bean method to obtain the service class.
To obtain the ApplicationContext class, you must implement the ApplicationContextAware interface, as follows:
import org.springframework.beans.BeansException; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; public class ApplicationContextUtil implements ApplicationContextAware { private static ApplicationContext context; public void setApplicationContext(ApplicationContext context) throws BeansException { this.context = context; } public static ApplicationContext getContext() { return context; } }
Then use the above method in the run method to create a business object, as follows:
XXXServiceI xxxService = ApplicationContextUtil.getContext.getBean(XXXServiceI.class);
This way it can be used normally The business class is over.
2. Inherit the Runnable interface, implement the run method, and perform operations in the run method. You need to pass in the instance object of the current class to create a Thread instance, and then call the start method to start the thread 3. Implement the Callable interface and rewrite the call() method. It should be noted that the first two methods do not require a response and are executed directly. However, if you implement the Callable interface and rewrite the call() method, You need to wait for the thread to respond, so although other threads are started, one thread is executing, and it cannot be considered a standard multi-thread. 4. Thread pool#Use @Aysnc annotation to implement multi-threadingThe same class , method A refers to method B. Adding asynchronous @Async annotation to method B will not be effectiveThe added @Async method and the caller cannot be in the same classThe difference between user threads and daemon threads Threads created in Java default to creating user threads, such as new Thread (thread object).start
Thread thread = new Thread(); // 默认为false,都是用户线程 thread.setDaemon(true); // 表示设置为守护线程 thread.setDaemon(false); // 表示设置为用户线程
User thread: No It dies as other threads die. There are only two situations where it dies. One is that it terminates due to an exception during operation, and the other is that the program is executed normally and the thread dies
Daemon thread: Dies as the user thread dies. When the user thread dies, the daemon thread also dies, such as the gc garbage collection thread. If the user thread exists, then gc needs to be alive, otherwise it will be useless.
public class Demo1 { public synchronized void functionA(){ System.out.println("iAmFunctionA"); functionB(); } public synchronized void functionB(){ System.out.println("iAmFunctionB"); }
When the task cache queue of the thread pool is full and the number of threads in the thread pool reaches maximumPoolSize, if there are still tasks arriving, the task rejection strategy will be adopted. Usually there are The following four strategies:
ThreadPoolExecutor.AbortPolicy
: Discard the task and throw RejectedExecutionException.
ThreadPoolExecutor.DiscardPolicy
: Discard the task, but do not throw an exception.
ThreadPoolExecutor.DiscardOldestPolicy
: Discard the frontmost task of the queue, and then resubmit the rejected task
ThreadPoolExecutor.CallerRunsPolicy
: By the calling thread ( The thread that submitted the task) processes the task
sleep is a method in the thread, but wait is a method in Object
The sleep method will not release the lock, but wait will release it and will be added to the waiting queue
sleep does not need to be awakened, but wait does
The lock level in java is the object level instead of the thread level. Each object has a lock, which is obtained through the thread. If the wait() method is in a thread, it is not obvious which lock the thread is waiting for.
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