Java 中的资源试用功能
在 Java 中， Try-with-resources 语句是一个 Try 语句，它声明了其中的一个或多个资源。资源是一个对象，一旦您的程序使用完它，就必须关闭它。例如，文件资源或套接字连接资源。try-with-resources 语句确保在语句执行结束时关闭每个资源。如果我们不关闭资源，它可能会构成资源泄漏，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，这包括实现 java.io.Closeable 的所有对象。
这样，现在我们不需要为了传递资源的结束语句而额外增加一个final block。一旦 try-catch 块被执行，资源将被关闭。
语法:试用资源
try(declare resources here) {
// use resources
}
catch(FileNotFoundException e) {
// exception handling
}
异常:
说到异常，try-catch-finally 块和 try-with-resources 块是有区别的。如果在 try 块和 final 块中都引发了异常，则该方法返回在 final 块中引发的异常。
对于 try-with-resources，如果在 try 块和 try-with-resources 语句中引发异常，则该方法返回在 try 块中引发的异常。资源尝试引发的异常被抑制，也就是说，我们可以说资源尝试块引发了被抑制的异常。
现在，让我们讨论两种可能的情况，下面以一个例子演示如下:
- 案例 1 :单一资源
- 案例 2: 多个资源
示例 1: 试用具有单个资源的资源
Java 语言(一种计算机语言，尤用于创建网站)
// 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: 尝试具有多个资源的资源
Java 语言(一种计算机语言，尤用于创建网站)
// 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
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