java-7 - 我是否正确使用了 Java 7 try-with-resources

Question

如果抛出异常，我希望缓冲读取器和文件读取器关闭并释放资源。

public static Object[] fromFile(String filePath) throws FileNotFoundException, IOException
{
    try (BufferedReader br = new BufferedReader(new FileReader(filePath)))
    {
        return read(br);
    } 
}

但是，是否需要有 catch 子句才能成功关闭？

编辑:

本质上，Java 7 中的上述代码是否等同于 Java 6 中的以下代码:

public static Object[] fromFile(String filePath) throws FileNotFoundException, IOException
{

    BufferedReader br = null;

    try
    {
        br = new BufferedReader(new FileReader(filePath));

        return read(br);
    }
    catch (Exception ex)
    {
        throw ex;
    }
    finally
    {
        try
        {
            if (br != null) br.close();
        }
        catch(Exception ex)
        {
        }
    }

    return null;
}

Answer 1

这是正确的，并且不需要 catch 子句。 Oracle java 7 文档表示，无论是否实际抛出异常，资源都将被关闭。

仅当您想对异常使用react时，才应使用 catch 子句。 catch 子句将在资源关闭后执行。

这是来自 Oracle's tutorial 的片段:

The following example reads the first line from a file. It uses an instance of BufferedReader to read data from the file. BufferedReader is a resource that must be closed after the program is finished with it:

static String readFirstLineFromFile(String path) throws IOException {
    try (BufferedReader br =
                   new BufferedReader(new FileReader(path))) {
        return br.readLine();
    }
} // In this example, the resource declared in the try-with-resources statement is a BufferedReader.

... Because the BufferedReader instance is declared in a try-with-resource statement, it will be closed regardless of whether the try statement completes normally or abruptly (as a result of the method BufferedReader.readLine throwing an IOException).

编辑

关于新编辑的问题:

Java 6 中的代码执行 catch ，然后执行 finally block 。这会导致资源仍然可能在 catch block 中打开。

在 Java 7 语法中，资源在 catch block 之前关闭，因此在 catch block 执行期间资源已关闭。这记录在上面的链接中:

In a try-with-resources statement, any catch or finally block is run after the resources declared have been closed.