虛擬機(jī)規(guī)范規(guī)定了類(lèi)加載器的父委托機(jī)制，但是由于運(yùn)行時(shí)包（命名空間）的問(wèn)題，存在隔離，書(shū)中提到，但凡是經(jīng)過(guò)的類(lèi)加載都會(huì)保存一份class文件，但是我運(yùn)行自定義類(lèi)加載器，多次加載java.lang.String類(lèi)，為什么第二次沒(méi)有在本地沒(méi)有緩存，是忘記需要重寫(xiě)那個(gè)方法嗎?

相關(guān)代碼

public class MyClassLoader extends ClassLoader {

  private static Path classDir = Paths.get("/Users/echo/");

  public MyClassLoader() {
    super();
  }

  @Override
  protected Class<?> findClass(String name) throws ClassNotFoundException {
    byte[] classBytes = readClassBytes(name);
    if (null == classBytes || classBytes.length == 0) {
      throw new ClassNotFoundException("can not load the class " + name + ".");
    }
    return defineClass(name, classBytes, 0, classBytes.length);
  }

  private byte[] readClassBytes(String name) throws ClassNotFoundException {
    String classPath = name.replace(".", File.separator);
    Path classFullPath = classDir.resolve(Paths.get(classPath + ".class"));
    if (!classFullPath.toFile().exists()) {
      throw new ClassNotFoundException("the class " + name + " not found.");
    }
    try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
      Files.copy(classFullPath, bos);
      return bos.toByteArray();
    } catch (IOException e) {
      throw new ClassNotFoundException("load the class " + name + " occur error.", e);
    }
  }

  @Override
  protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
    synchronized (getClassLoadingLock(name)) {
      Class<?> c = findLoadedClass(name);
      if (c != null) {
        System.out.println("在自定義加載器緩存中找到.");
      }
      if (c == null) {
        long t0 = System.nanoTime();
        try {
          if (getParent() != null) {
            c = getParent().loadClass(name);
            if (c != null) {
              System.out.println("在父類(lèi)加載器中找到.");
            }
          } else {
            c = getSystemClassLoader().loadClass(name);
            if (c != null) {
              System.out.println("直接在根加載器中找到.");
            }
          }
        } catch (ClassNotFoundException e) {

        }
        if (c == null) {
          long t1 = System.nanoTime();
          c = findClass(name);
          if (c != null) {
            System.out.println("在自定義加載器中找到.");
          }
        }
      }
      if (resolve) {
        resolveClass(c);
      }
      return c;
    }
  }
}

    MyClassLoader classLoader = new MyClassLoader();
    classLoader.loadClass("java.lang.String");
    try {
      TimeUnit.SECONDS.sleep(5);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    classLoader.loadClass("java.lang.String");