假如在构造方法中打开了资源，应该在何处清理和回收资源？

假如在构造方法中打开了资源，应该在何处清理和回收资源？

作为一个程序员，你在编码的时候，应该时刻询问自己“如果异常发生了，所有东西能被正确的清理吗？”。

如下面的例子，在构造方法中打开了资源，是否能在构造器中加上try-catch模块，在finally中回收资源呢？

//: exceptions/InputFile.java
// Paying attention to exceptions in constructors.
import java.io.*;

public class InputFile {
  private BufferedReader in;
  public InputFile(String fname) throws Exception {
    try {
      in = new BufferedReader(new FileReader(fname));
      // Other code that might throw exceptions
    } catch(FileNotFoundException e) {
      System.out.println("Could not open " + fname);
      // Wasn't open, so don't close it
      throw e;
    } catch(Exception e) {
      // All other exceptions must close it
      try {
        in.close();
      } catch(IOException e2) {
        System.out.println("in.close() unsuccessful");
      }
      throw e; // Rethrow
    } finally {
      // Don't close it here!!!
    }
  }
  public String getLine() {
    String s;
    try {
      s = in.readLine();
    } catch(IOException e) {
      throw new RuntimeException("readLine() failed");
    }
    return s;
  }
  public void dispose() {
    try {
      in.close();
      System.out.println("dispose() successful");
    } catch(IOException e2) {
      throw new RuntimeException("in.close() failed");
    }
  }
} ///:~

该场景中，不能在构造方法的finally中回收资源，因为对象的其它方法需要使用资源，所以需要在调用对象方法结束时，单独调用对象的回收资源方法。

如：

//: exceptions/Cleanup.java
// Guaranteeing proper cleanup of a resource.

public class Cleanup {
  public static void main(String[] args) {
    try {
      InputFile in = new InputFile("Cleanup.java");
      try {
        String s;
        int i = 1;
        while((s = in.getLine()) != null)
          ; // Perform line-by-line processing here...
      } catch(Exception e) {
        System.out.println("Caught Exception in main");
        e.printStackTrace(System.out);
      } finally {
        in.dispose();
      }
    } catch(Exception e) {
      System.out.println("InputFile construction failed");
    }
  }
} /* Output:
dispose() successful
*///:~