如果我们使用 try-with-resource 是否需要关闭资源

Question

我在我的代码中使用了 try-with-resource 块，想知道是否需要在方法结束时关闭资源，或者不需要？

try (S3Object object = s3.getObject(new GetObjectRequest(bucketName, key));
  BufferedReader br = new BufferedReader(new InputStreamReader(object.getObjectContent()));
  BufferedWriter bw = new BufferedWriter(new FileWriter(new File("output.txt")))){
  String line;

  while((line=br.readLine())!=null){
    bw.write(line);
    bw.newLine();
    bw.flush();
  }
}

Answer 1

没有

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.

如果您使用的是 java 6 或更早版本：

Prior to Java SE 7, you can use a finally block to ensure that a resource is closed regardless of whether the try statement completes normally or abruptly.

更新：

You may declare one or more resources in a try-with-resources statement.

正如您在代码中使用的那样。

Answer 2

不，你不知道。我们来看一个 try-catch-finally 和 try-with-resource

的例子

Scanner scanner = null;
try {
    scanner = new Scanner(new File("test.txt"));
    while (scanner.hasNext()) {
        System.out.println(scanner.nextLine());
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} finally {
    if (scanner != null) {
        scanner.close();
    }
}

这是您的常规 try-catch-finally，您将关闭 finally 块中的扫描器。现在让我们来看看 try-with-resource

try (Scanner scanner = new Scanner(new File("test.txt"))) {
    while (scanner.hasNext()) {
        System.out.println(scanner.nextLine());
    }
} catch (FileNotFoundException fnfe) {
    fnfe.printStackTrace();
}

您不需要在此处关闭 scanner，因为它会在 try 块执行完毕后自行关闭。如需更多参考，请访问此 blog

Answer 3

您不必关闭您在 try 子句中定义的资源。但是，根据你的例子，你在 body 的 try:

中也有这个

BufferedWriter bw = new BufferedWriter(new FileWriter(new File("output.txt"))))

并且您的代码没有关闭该资源。这是错误的（保持文件系统句柄打开很可能是真正的资源泄漏）。

换句话说：您可能想将 bw 添加到您的 try-with-resources 子句中，因此它与 S3Object object 的定义一致（请参阅了解示例 ).

如果我们使用 try-with-resource 是否需要关闭资源

Is there a need to close resource if we use try-with-resource

java

try-with-resources