我是否正确地使用了 Java7的 try-with-resources

如果抛出异常，我希望关闭缓冲的读取器和文件读取器，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，是否需要有一个 catch子句才能成功关闭？

编辑:

基本上，以上 Java7中的代码是否等同于以下 Java6中的代码:

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;
}

64705

小开

最佳答案

It's correct and there's no requirement for catch clause. Oracle java 7 doc says the resource will be closed regardless of whether an exception is actually thrown or not.

You should use a catch clause only if you want to react upon the exception. The catch clause will be executed after the resource is closed.

Here's a snippet from Oracle's tutorial:

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).

EDIT

Regarding the new edited question:

The code in Java 6 executes the catch and afterwards the finally block. This causes the resources to be still potentially opened in the catch block.

In Java 7 syntax, resources are closed before the catch block, so resources are already closed during the catch block execution. This is documented in the above link:

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

public static Object[] fromFile(String filePath) throws FileNotFoundException, IOException { int sz = /* get buffer size somehow */ try (BufferedReader br = new BufferedReader(new FileReader(filePath), sz)) { return read(br); } }

public static Object[] fromFile(String filePath) throws FileNotFoundException, IOException { int sz = /* get buffer size somehow */ try (FileReader file = new FileReader(filePath); BufferedReader br = new BufferedReader(file, sz)) { return read(br); } }