在此之前，我一直使用`try-catch-finally`的`catch`或`finally`语句块关闭资源，比如输入流、输出流、读写流等。 比如下面的例子：当读入流或写出流出现异常时，我们需要在`catch`语句块中对其执行资源关闭操作。而读写流的`close`方法本身就会抛出`IOException`，也需要处理异常。 ```java /** * @author: miantiao * @date: 2021/9/14 */ public class TryCatch { public static void main(String[] args) { String path = "F:\\test.txt"; String newPath = "F:\\new.txt"; BufferedReader bufferedReader = null; BufferedWriter bufferedWriter = null; File readFile = new File(path); File writeFile = new File(newPath); try { bufferedReader = new BufferedReader(new FileReader(readFile)); bufferedWriter = new BufferedWriter(new FileWriter(writeFile)); String s = ""; while ((s = bufferedReader.readLine()) != null) { bufferedWriter.write(s); } bufferedWriter.flush(); } catch (Exception e) { //关闭读入流 try { bufferedReader.close(); } catch (IOException e1) { e1.printStackTrace(); } //关闭写出流 try { bufferedWriter.close(); } catch (IOException e1) { e1.printStackTrace(); } } } } ``` 在这种情况下如果只涉及一种资源的关闭还好说，但有多个资源时就会出现一种奇观，那就是在执行第一种资源的关闭操作时出现异常，那么剩余的资源都没有办法正常关闭。 然而JDK在1.7版本中就提供了一种优雅的关闭资源的方式`try-with-resources`（不是今天遇到问题，我都发现不了，真的菜的真实~~） > The try-with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try-with-resources statement ensures that each resource is closed at the end of the statement. Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource. 上面是Oracle官方给出的对`try-with-resources`的解释：`try-with-resources`语句是一种声明一个或多个资源的`try`语句。 资源是程序完成后必须关闭的对象。`try-with-resources`语句确保每个资源在语句结束时关闭。 任何实现`java.lang.AutoCloseable`的对象，包括实现`java.io.Closeable`的所有对象，都可以用作资源。 这真的太友好了，再也不需要我用我这小脑瓜子想如何关闭资源了。以上面的代码为例，可以用`try-with-resources`改造如下： ```java /** * @author: miantiao * @date: 2021/9/14 */ public class TryWithResource { public static void main(String[] args) { String path = "F:\\test.txt"; String newPath = "F:\\new.txt"; File readFile = new File(path); File writeFile = new File(newPath); try (BufferedReader bufferedReader = new BufferedReader(new FileReader(readFile)); BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(writeFile))) { String s = ""; while ((s = bufferedReader.readLine()) != null) { bufferedWriter.write(s); } bufferedWriter.flush(); } catch (Exception e) { e.printStackTrace(); } } } ``` 但是值得注意的是只有实现了`java.lang.AutoCloseable`接口或实现了`java.io.Closeable`接口的对象，才可以使用`try-with-catch`语法来关闭资源。其中，Closeable接口是继承自AutoCloseable接口的。 ```java /** * A {@code Closeable} is a source or destination of data that can be closed. * The close method is invoked to release resources that the object is * holding (such as open files). * * @since 1.5 */ public interface Closeable extends AutoCloseable {} ``` 上述例子中，`BufferedReader`和`BufferedWriter`都间接实现了Closeable接口。 ```java //BufferedReader 的继承关系 public class BufferedReader extends Reader public abstract class Reader implements Readable, Closeable //BufferedWriter 的继承关系 public class BufferedWriter extends Writer public abstract class Writer implements Appendable, Closeable, Flushable ``` Reference: [The try-with-resources Statement](https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html)