java - 非公共(public)构造函数导致 Tomcat7 出现问题？

Question

我有一个在 tomcat 上运行 Spring 的 Java 应用程序。

这个类给我带来了一个非常奇怪的问题:

@WebListener
public class ThreadPool extends ThreadPoolExecutor implements ServletContextListener {

  private ThreadPool() {
    super(MIN_ACTIVE_THREADS, MAX_ACTIVE_THREADS, DEACTIVATE_THREADS_AFTER_TIMEPERIOD, TimeUnit.SECONDS, taskQueue);
  }

  private static final ThreadPoolExecutor pool = new ThreadPool();

  public synchronized static void submit(Task task) {
      executingTasks.add(task);
      pool.execute(task);
  }

  @Override
  public synchronized void contextDestroyed(ServletContextEvent arg0) {
    cancelWaitingTasks();
    sendStopSignalsToExecutingTasks();
    pool.shutdown();
  }

  ...

}

如果构造函数是私有(private)的或默认的，我会在运行时遇到此异常(在对应用程序的第一个 HTTP 请求时):

Error configuring application listener of class com.testApp.util.ThreadPool
java.lang.IllegalAccessException: Class org.apache.catalina.core.DefaultInstanceManager can not access a member of class com.testApp.util.ThreadPool with modifiers "private"
    at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:102)
    at java.lang.Class.newInstance(Class.java:436)
    at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:140)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4888)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5467)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
Skipped installing application listeners due to previous error(s)
Error listenerStart
Context [] startup failed due to previous errors

但是，如果我将构造函数设置为 public，那么我将不会出现异常，并且一切正常。谁能告诉我为什么这个默认或私有(private)构造函数会导致运行时异常？

Answer 1

Tomcat 使用 Class.newInstance()创建一个 ThreadPool 的实例.此方法遵循 Java 的访问规则。

因为你的构造函数是私有(private)的，所以它失败了 IllegalAccessException .这是运行时等效于不允许调用编译器错误的函数，如果您尝试编写 new ThreadPool() 就会看到该错误在ThreadPool之外,