The try-with-resources Statementtry-with-resources语句

The try-with-resources statement is a try statement that declares one or more resources.try-with-resources语句是声明一个或多个资源的try语句。A resource is an object that must be closed after the program is finished with it.资源是一个必须在程序完成后关闭的对象。The try-with-resources statement ensures that each resource is closed at the end of the statement.try-with-resources语句确保在语句末尾关闭每个资源。Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.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。

The following example reads the first line from a file.下面的示例从文件中读取第一行。It uses an instance of BufferedReader to read data from the file.它使用BufferedReader实例从文件中读取数据。BufferedReader is a resource that must be closed after the program is finished with it:BufferedReader是程序完成后必须关闭的资源：

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.在本例中，try-with-resources语句中声明的资源是BufferedReader。The declaration statement appears within parentheses immediately after the try keyword.声明语句出现在try关键字后面的括号内。The class BufferedReader, in Java SE 7 and later, implements the interface java.lang.AutoCloseable.Java SE 7及更高版本中的BufferedReader类实现了接口Java.lang.AutoCloseable。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).由于BufferedReader实例是在try-with-resource语句中声明的，因此无论try语句是正常完成还是突然完成（由于BufferedReader.readLine方法引发IOException），它都将关闭。

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.在Java SE 7之前，您可以使用finally块来确保资源关闭，而不管try语句是正常完成还是突然完成。The following example uses a finally block instead of a try-with-resources statement:以下示例使用finally块而不是try-with-resources语句：

static String readFirstLineFromFileWithFinallyBlock(String path)
  throws IOException {
    BufferedReader br = new BufferedReader(new FileReader(path));
    try {
        return br.readLine();
    } finally {
        br.close();
    }
}

However, in this example, if the methods readLine and close both throw exceptions, then the method readFirstLineFromFileWithFinallyBlock throws the exception thrown from the finally block; the exception thrown from the try block is suppressed.但是，在本例中，如果readLine和close方法都抛出异常，那么readFirstLineFromFileWithFinallyBlock方法抛出finally块抛出的异常；从try块引发的异常被抑制。In contrast, in the example readFirstLineFromFile, if exceptions are thrown from both the try block and the try-with-resources statement, then the method readFirstLineFromFile throws the exception thrown from the try block; the exception thrown from the try-with-resources block is suppressed.相反，在示例readFirstLineFromFile中，如果从try块和try-with-resources语句抛出异常，则方法readFirstLineFromFile抛出从try块抛出的异常；从try-with-resources块引发的异常被抑制。In Java SE 7 and later, you can retrieve suppressed exceptions; see the section Suppressed Exceptions for more information.在JavaSE7和更高版本中，您可以检索被抑制的异常；有关更多信息，请参阅抑制异常一节。

You may declare one or more resources in a try-with-resources statement.您可以在try-with-resources语句中声明一个或多个资源。The following example retrieves the names of the files packaged in the zip file zipFileName and creates a text file that contains the names of these files:以下示例检索打包在zip文件zipFileName中的文件名，并创建包含这些文件名的文本文件：

public static void writeToFileZipFileContents(String zipFileName,
                                           String outputFileName)
  throws java.io.IOException {
    java.nio.charset.Charset charset =
         java.nio.charset.StandardCharsets.US_ASCII;
    java.nio.file.Path outputFilePath =
         java.nio.file.Paths.get(outputFileName);

    // Open zip file and create output file with 
    // try-with-resources statement

    try (
        java.util.zip.ZipFile zf =
             new java.util.zip.ZipFile(zipFileName);
        java.io.BufferedWriter writer = 
            java.nio.file.Files.newBufferedWriter(outputFilePath, charset)
    ) {
        // Enumerate each entry
        for (java.util.Enumeration entries =
                                zf.entries(); entries.hasMoreElements();) {
            // Get the entry name and write it to the output file
            String newLine = System.getProperty("line.separator");
            String zipEntryName =
                 ((java.util.zip.ZipEntry)entries.nextElement()).getName() +
                 newLine;
            writer.write(zipEntryName, 0, zipEntryName.length());
        }
    }
}

In this example, the try-with-resources statement contains two declarations that are separated by a semicolon: ZipFile and BufferedWriter.在本例中，try-with-resources语句包含两个用分号分隔的声明：ZipFile和BufferedWriter。When the block of code that directly follows it terminates, either normally or because of an exception, the close methods of the BufferedWriter and ZipFile objects are automatically called in this order.当直接跟随它的代码块终止时，无论是正常终止还是由于异常而终止，BufferedWriter和ZipFile对象的close方法都会按此顺序自动调用。Note that the close methods of resources are called in the opposite order of their creation.请注意，资源的close方法的调用顺序与其创建顺序相反。

The following example uses a try-with-resources statement to automatically close a java.sql.Statement object:以下示例使用try-with-resources语句自动关闭java.sql.Statement对象：

public static void viewTable(Connection con) throws SQLException {
    String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES";
    try (Statement stmt = con.createStatement()) {
        ResultSet rs = stmt.executeQuery(query);

        while (rs.next()) {
            String coffeeName = rs.getString("COF_NAME");
            int supplierID = rs.getInt("SUP_ID");
            float price = rs.getFloat("PRICE");
            int sales = rs.getInt("SALES");
            int total = rs.getInt("TOTAL");

            System.out.println(coffeeName + ", " + supplierID + ", " + 
                               price + ", " + sales + ", " + total);
        }
    } catch (SQLException e) {
        JDBCTutorialUtilities.printSQLException(e);
    }
}

The resource java.sql.Statement used in this example is part of the JDBC 4.1 and later API.本例中使用的资源java.sql.Statement是JDBC 4.1及更高版本API的一部分。

Note: A try-with-resources statement can have catch and finally blocks just like an ordinary try statement.注意：try-with-resources语句可以像普通try语句一样具有catch和finally块。In a try-with-resources statement, any catch or finally block is run after the resources declared have been closed.在try-with-resources语句中，任何catch或finally块都会在声明的资源关闭后运行。

Suppressed Exceptions抑制异常

An exception can be thrown from the block of code associated with the try-with-resources statement.可以从与try-with-resources语句关联的代码块中引发异常。In the example writeToFileZipFileContents, an exception can be thrown from the try block, and up to two exceptions can be thrown from the try-with-resources statement when it tries to close the ZipFile and BufferedWriter objects.在示例writeToFileZipFileContents中，可以从try块引发异常，当try-with-resources语句尝试关闭ZipFile和BufferedWriter对象时，最多可以从try-with-resources语句引发两个异常。If an exception is thrown from the try block and one or more exceptions are thrown from the try-with-resources statement, then those exceptions thrown from the try-with-resources statement are suppressed, and the exception thrown by the block is the one that is thrown by the writeToFileZipFileContents method.如果从try块引发异常，并且从try-with-resources语句引发一个或多个异常，则从try-with-resources语句引发的异常将被抑制，并且该块引发的异常是writeToFileZipFileContents方法引发的异常。You can retrieve these suppressed exceptions by calling the Throwable.getSuppressed method from the exception thrown by the try block.通过从try块抛出的异常调用Throwable.getSuppressed方法，可以检索这些被抑制的异常。

Classes That Implement the AutoCloseable or Closeable Interface实现自动关闭或可关闭接口的类

See the Javadoc of the AutoCloseable and Closeable interfaces for a list of classes that implement either of these interfaces.请参阅AutoCloseable接口和Closeable接口的Javadoc，了解实现这两个接口的类的列表。The Closeable interface extends the AutoCloseable interface.Closeable接口扩展了AutoCloseable接口。The close method of the Closeable interface throws exceptions of type IOException while the close method of the AutoCloseable interface throws exceptions of type Exception.Closeable接口的close方法引发IOException类型的异常，而AutoCloseable接口的close方法引发Exception类型的异常。Consequently, subclasses of the AutoCloseable interface can override this behavior of the close method to throw specialized exceptions, such as IOException, or no exception at all.因此，AutoCloseable接口的子类可以重写close方法的这种行为，以抛出专门的异常，例如IOException，或者根本不抛出异常。