try-with-resources

try-with-resources 是 JDK 7 中一个新的异常处理机制，它能够很容易地关闭在 try-catch 语句块中使用的资源。资源（resource）是指在程序完成后，必须关闭的对象。try-with-resources 语句确保了每个资源在语句结束时关闭。所有实现了 java.lang.AutoCloseable 接口（其中，它包括实现了 java.io.Closeable 的所有对象），可以使用作为资源。

传统写法：try-catch-finally

public static void main(String[] args) {
    BufferedInputStream bin = null;
    BufferedOutputStream bout = null;
    try {
        bin = new BufferedInputStream(new FileInputStream(new File("")));
        bout = new BufferedOutputStream(new FileOutputStream(new File("")));
        while ((b = bin.read()) != -1) {
            bout.write(b);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (bin != null) {
            try {
                bin.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

JDK 7：try-with-resources

public static void main(String[] args) {
    try (BufferedInputStream bin = new BufferedInputStream(new FileInputStream(new File("")));
         BufferedOutputStream bout = new BufferedOutputStream(new FileOutputStream(new File("")))) {
        while ((b = bin.read()) != -1) {
            bout.write(b);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

JDK 9：
try-with-resources 声明在 JDK 9 已得到改进。如果你已经有一个资源是 final 或等效于 final 变量,您可以在 try-with-resources 语句中使用该变量，而无需在 try-with-resources 语句中声明一个新变量。

public static void main(String[] args) throws Exception {
    BufferedInputStream bin = new BufferedInputStream(new FileInputStream(new File("")));
    BufferedOutputStream bout = new BufferedOutputStream(new FileOutputStream(new File("")));
    try (bin;bout) {
        while ((b = bin.read()) != -1) {
            bout.write(b);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

资源必须实现 AutoClosable 接口，并重写 close 方法

public class Connection implements AutoCloseable {
	@Override
	public void close(){
	}
}