java - 为什么 newInstance 在我的代码中抛出 InstantiationException？

Question

这个问题已经有答案了:

Can I use Class.newInstance() with constructor arguments? (9 个回答)

已关闭 6 年前。

我有两个流程，如下所示。我的每个进程都有run和shutdown方法

Process processA = new ProcessA("processA", getProcessAProperties());
Process processB = new ProcessB("processB", getProcessBProperties());

• 我希望每个进程有不同的线程池配置，以便 ProcessA 在自己的线程池中运行，而 ProcessB 在自己的线程池中运行，彼此独立。
• 而且我无法在其自己的线程池的每个线程之间共享 Process 对象。

下面是我的 Process 类和我的 ProcessA 的样子, ProcessB类只是扩展 Process 类。我在 run 方法中做了所有重要的事情。

public abstract class Process implements Runnable {
  private Properties props;
  private String processName;

  public Process(String processName, Properties props) {
    this.processName = processName;
    this.props = props;
  }

  protected abstract void shutdown();

  protected abstract void run(String processName, Properties props);

  @Override
  public final void run() {
    run(processName, props);
  }

  public Properties getProps() {
    return props;
  }

  public void setProps(Properties props) {
    this.props = props;
  }

  public String getProcessName() {
    return processName;
  }

  public void setProcessName(String processName) {
    this.processName = processName;
  }
}

下面是我如何运行 ProcessA 的简单示例有自己的线程池。 共有三个线程，每个线程都有自己的 ProcessA 对象来处理。现在我想以更通用的方式扩展它，以便它可以适用于我的进程 ProcessA和ProcessB .

public static void main(String[] args) {
  int numberOfThreads = 3;
  ExecutorService executor = Executors.newFixedThreadPool(numberOfThreads);

  final List<Process> processes = new ArrayList<>();
  for (int i = 0; i < numberOfThreads; i++) {
    // each thread works on different Process object
    Process processA = new ProcessA("processA", getProcessAProperties());
    processes.add(processA);
    executor.submit(processA);
  }

  Runtime.getRuntime().addShutdownHook(new Thread() {
    @Override
    public void run() {
      for (Process process : processes) {
        process.shutdown();
      } 
      executor.shutdown();
      try {
        executor.awaitTermination(5000, TimeUnit.MILLISECONDS);
      } catch (InterruptedException e) {
        e.printStackTrace;
      }
    }
  });
}

为了以更通用的方式解决这个问题，我创建了一个 Process handler，如下所示:

public final class ProcessHandler {
  private final ExecutorService executorServiceProcess;
  private final List<Process> processes = new ArrayList<>();
  private final Thread shutdownHook = new Thread() {
    @Override
    public void run() {
      for (Process process : processes)
        process.shutdown();
      executorServiceProcess.shutdown();
    }
  };

  public ProcessHandler(Process process, int poolSize) {
    this.executorServiceProcess = Executors.newFixedThreadPool(poolSize);
    Runtime.getRuntime().addShutdownHook(shutdownHook);
    for (int i = 0; i < poolSize; i++) {
      try {
        // this line throws exception
        Process p = process.getClass().newInstance();
        p.setProcessName(process.getProcessName());
        p.setProps(process.getProps());
        processes.add(p);
        executorServiceProcess.submit(p);
      } catch (InstantiationException | IllegalAccessException e) {
        e.printStackTrace();
      }
    }
  }

  public void shutdown() {
    Runtime.getRuntime().removeShutdownHook(shutdownHook);
    shutdownHook.start();
    try {
      shutdownHook.join();
    } catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
    }
  }
}

这就是我的主要方法现在的样子:

public static void main(String[] args) {

    Process processA = new ProcessA("processA", getProcessAProperties());
    Process processB = new ProcessB("processB", getProcessBProperties());

    // processA will run with three threads in its own thread pool
    ProcessHandler processHandlerA = new ProcessHandler (processA, 3);
    // processB will run with two threads in its own thread pool
    ProcessHandler processHandlerB = new ProcessHandler (processB, 2);

    // now I can call shutdown on them
    processHandlerA.shutdown();
    processHandlerB.shutdown();
}

这行在我的 ProcessHandler类Process p = process.getClass().newInstance();抛出异常:

java.lang.InstantiationException: com.david.test.ProcessA

我不知道为什么InstantiationException被抛出了吗？

请注意:每个进程都是 kafka 消费者，通常 kafka 消费者不是线程安全的，所以这就是为什么我每次都必须创建一个新对象并提交给执行器。

更新:

这是我的 ProcessA 类，如下所示:

public class ProcessA extends Process {
  private KafkaConsumer<byte[], byte[]> consumer;

  public ProcessA(String processName, Properties props) {
    super(processName, props);
  }

  @Override
  public void shutdown() {
    consumer.wakeup();
  }

  @Override
  protected void run(String processName, Properties props) {
    consumer = new KafkaConsumer<>(props);
    System.out.println("Hello World");
    // do all kind of important stuff here
  }
}

Answer 1

您是否有一个扩展 Process 抽象类的具体类？

抽象类不能自行实例化，参见:http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html

也许尝试使用具体类扩展抽象类并创建具体类的实例，如果需要，您仍然可以将它们转换为 Process 对象。