Java的Try-with-resources 功能

在Java， Try-with-resources语句是一个 try 语句，它在其中声明一个或多个资源。资源是一个对象，一旦你的程序使用它就必须关闭它。例如，文件资源或套接字连接资源。 try-with-resources 语句确保每个资源在语句执行结束时关闭。如果我们不关闭资源，可能会造成资源泄漏，并且程序可能会耗尽可用的资源。

您可以将任何对象作为实现Java.lang.AutoCloseable的资源传递，其中包括实现Java.io.Closeable 的所有对象。

这样，现在我们不需要添加额外的 finally 块来传递资源的结束语句。执行 try-catch 块后，资源将立即关闭。

语法： Try-with-resources

try(declare resources here) {
    // use resources
}
catch(FileNotFoundException e) {
    // exception handling
}

例外：

当涉及到异常时，try-catch-finally 块和 try-with-resources 块是有区别的。如果 try 块和 finally 块中都抛出异常，则该方法返回 finally 块中抛出的异常。

对于 try-with-resources，如果在 try 块和 try-with-resources 语句中抛出异常，则该方法返回在 try 块中抛出的异常。 try-with-resources 抛出的异常被抑制，即我们可以说 try-with-resources 块抛出被抑制的异常。

现在，让我们讨论下面作为示例演示的两种可能场景，如下所示：

• 案例 1 ：单一资源
• 案例 2：多个资源

示例 1：具有单个资源的 try-with-resources

Java

// Java Program for try-with-resources
// having single resource
 
// Importing all input output classes
import java.io.*;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Try block to check for exceptions
        try (
 
            // Creating an object of FileOutputStream
            // to write stream or raw data
 
            // Adding resource
            FileOutputStream fos
            = new FileOutputStream("gfgtextfile.txt")) {
 
            // Custom string input
            String text
                = "Hello World. This is my java program";
 
            // Converting string to bytes
            byte arr[] = text.getBytes();
 
            // Text written in the file
            fos.write(arr);
        }
 
        // Catch block to handle exceptions
        catch (Exception e) {
 
            // Display message for the occured exception
            System.out.println(e);
        }
 
        // Display message for successful execution of
        // program
        System.out.println(
            "Resource are closed and message has been written into the gfgtextfile.txt");
    }
}

输出：

Resource are closed and message has been written into the gfgtextfile.txt

示例 2： try-with-resources 具有多个资源

Java

// Java program for try-with-resources
// having multiple resources
 
// Importing all input output classes
import java.io.*;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Try block to check for exceptions
 
        // Writing data to a file using FileOutputStream
        // by passing input file as a parameter
        try (FileOutputStream fos
             = new FileOutputStream("outputfile.txt");
 
             // Adding resouce
 
             // Reading the stream of character from
             BufferedReader br = new BufferedReader(
                 new FileReader("gfgtextfile.txt"))) {
 
            // Declaring a string holding the
            // stream content of the file
            String text;
 
            // Condition check using readLine() method
            // which holds true till there is content
            // in the input file
            while ((text = br.readLine()) != null) {
 
                // Reading from input file passed above
                // using getBytes() method
                byte arr[] = text.getBytes();
 
                // String converted to bytes
                fos.write(arr);
 
                // Copying the content of passed input file
                // 'inputgfgtext' file to outputfile.txt
            }
 
            // Display message when
            // file is successfully copied
            System.out.println(
                "File content copied to another one.");
        }
 
        // Catch block to handle generic exceptions
        catch (Exception e) {
 
            // Display the exception on the
            // console window
            System.out.println(e);
        }
 
        // Display message for successful execution of the
        // program
        System.out.println(
            "Resource are closed and message has been written into the gfgtextfile.txt");
    }
}

输出：

File content copied to another one.
Resource are closed and message has been written into the gfgtextfile.txt