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This article mainly explains "the usage scenario and practical application of try-with-resources in java". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "the usage scenario and practical application of try-with-resources in java".

1. At the beginning, the actual try-with-resources uses the following: / * read out binary files * * @ param filePath text absolute path * @ return * @ throws FileNotFoundException * @ throws IOException * / public static byte [] getReaderToBinary (String filePath) throws FileNotFoundException, IOException {int bufferSize = 4096; / / set buffer size byte buffer [] = new byte [bufferSize] / / buffer byte array File sourceFile = new File (filePath); byte [] b = null; try (InputStream fis = new FileInputStream (sourceFile); BufferedInputStream bis = new BufferedInputStream (fis, bufferSize);) {int len = bis.available (); b = new byte [len]; bis.read (b, 0, len) } return b;}

The reference address for the above example is:

* author: this person is too lazy * Source: CSDN * original: https://blog.csdn.net/qq_35546153/article/details/83421506 * copyright notice: this article is the original article of the blogger, please attach a link to the blog article to reprint it!

Previously, using try-catch-finally was more cumbersome and unintuitive, and even occasionally forgot to turn it off, as follows:

InputStream fis = null; BufferedInputStream bis = null; try {fis = new FileInputStream (sourceFile); bis = new BufferedInputStream (fis, bufferSize); int len = bis.available (); b = new byte [len]; bis.read (b, 0, len);} finally {if (fis! = null) {fis.close () } if (bis! = null) {bis.close ();}} 2, usage scenario

The use of try-with-resources is to define the resources that need to be closed in parentheses after the try keyword. Resources are automatically released after the try block is executed.

It is important to note, however, that not all code that is expected to be closed can be put into it, and only classes that implement the java.lang.AutoCloseable interface can be closed automatically.

Eg: InputStream in the above code example, which is defined as follows:

Public abstract class InputStream implements Closeable

And Closeable, which is defined as follows (from jdk1.5 version):

/ * * A {@ code Closeable} is a source or destination of data that can be closed. * The close method is invoked to release resources that the object is * holding (such as open files). * * @ since 1.5 * / public interface Closeable extends AutoCloseable

Description:

1. Try-with-resource syntax is added since JDK7.

2. It's just a syntactic sugar: when you decompile the above code, you will find that for the JVM virtual machine, it still sees the previous try-catch-finally writing.

3. Practical use

Most of the scenes are opened with external resources:

File

Database connection

Network connection

Etc.

If there are custom requirements:

Public class CustomResource implements java.lang.AutoCloseable {@ Override public void close () {System.out.printf ("close method of [% s] called\ n", this.getClass (). GetName ());} public static void main (String [] args) {try (CustomResource customResource = new CustomResource ();) {/ / do something System.out.println ("do something") Throw new RuntimeException ("Test throws an unknown exception");}

The console output is as follows:

Do somethingException in thread "main" java.lang.RuntimeException: test throws an unknown exception at com.xxx.main (CustomResource.java:22) calls the close method of [com.xxx.CustomResource]

Note: even if an exception is thrown in the try block, it does not affect the shutdown of the resource

4. Other key points

Note:

Public class CustomResource implements java.lang.AutoCloseable {public CustomResource () {throw new RuntimeException ("Constructor exception:" + this.getClass () .getName ());} @ Override public void close () {System.out.printf ("close method of [% s] called\ n", this.getClass () .getName ()); throw new RuntimeException ("close method exception:" + this.getClass () .getName () } public static void main (String [] args) {try (CustomResource customResource = new CustomResource ();) {/ / do something System.out.println ("do something");} catch (Exception e) {System.out.println ("do catch"); e.printStackTrace ();}

The console output is as follows:

Do catchjava.lang.RuntimeException: constructor exception: com.xxx.CustomResource at com.xxx.CustomResource. (CustomResource.java:13) at com.xxx.CustomResource.main (CustomResource.java:24)

Explanation (reference address: https://www.cnblogs.com/itZhy/p/7636615.html):

During try-with-resource, if both the handling of external resources and the closure of external resources encounter exceptions, the "close exception" will be suppressed and the "handle exception" will be thrown, but the "close exception" will not be lost, but will be stored in the list of suppressed exceptions in the "handling exception".

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