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回复”666“获取新整理的面试文章

现在你多少听说一些JDK9 JShell相关的内容，这篇文章中将介绍如何使用JShell像Unix脚本一样执行Java代码。

让我们开始一个简单的例子，再进行详细的介绍：

• 创建一个 java_shell_code.txt 的文件；

• 在文件中写一些Java代码，并执行以下命令。你没必须声明一个Class，你可以直接写一句代码，或者创建一个方法。

java ex.jshell.extension.JShellScriptExecutor ./java_shell_code.txt

java_shell_code.txt

// java_shell_code.txt contents./* If you observe it does not need a class declaration.Using the power of jshell, we can write functions and call functions with out creating class, just like functional programming */// You can also include comments like above, anywhere in the scriptString var1 = "Hello";System.out.println(var1);public int getInt1(){return 2;}public int getInt2(){return 4;}getInt1() + getInt2();public class MyClass{public void sayHelloWorld(){System.out.println("HelloWorld");}}new MyClass().sayHelloWorld()

执行结果：

"Hello"Hello6HelloWorld

详细介绍

在JDK9中提供了一个新的类 JShell.java，它属于jdk.jshell模块。我们可以使用它执行Java代码片段，或创建一个Java方法，而不用创建一个类。如果这个Java代码片段中有错误，可以通过 Snippet.status状态（只有两种状态：REJECTED、VALID）来检查。SourceCodeAnalysis是用来解析代码的，它使用分号、解析方法、或类的声明等。

下面是JShellScriptExecutor代码。你可以拷贝，并修改它。你也可以从GitHub仓库中克隆。

https://github.com/kotari4u/jshell_script_executor

package ex.jshell.extension;
import jdk.jshell.JShell;
import jdk.jshell.Snippet;
import jdk.jshell.SnippetEvent;
import jdk.jshell.SourceCodeAnalysis;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Objects;
/*** This class can execute jshell expressions in sequence* We can write java commands like shell script and execute it.* Just write commands in a way that we give in jshell and save it in a file and execute it.** @author Hemamabara Vamsi, Kotari* @since 5/27/2017.*/
public class JShellScriptExecutor {public static void main(String[] args){new JShellScriptExecutor().evaluate(args[0]);}public void evaluate(String scriptFileName){try(JShell jshell = JShell.create()){// Handle snippet events. We can print value or take action if evaluation failed.jshell.onSnippetEvent(snippetEvent -> snippetEventHandler(snippetEvent));String scriptContent = new String(Files.readAllBytes(Paths.get(scriptFileName)));String s = scriptContent;while (true) {// Read source line by line till semicolon (;)SourceCodeAnalysis.CompletionInfo an = jshell.sourceCodeAnalysis().analyzeCompletion(s);if (!an.completeness().isComplete()) {break;}// If there are any method declaration or class declaration // in new lines, resolve it.jshell.eval(trimNewlines(an.source()));// EOFif (an.remaining().isEmpty()) {break;}// If there is semicolon, execute next seqs = an.remaining();}} catch (IOException e) {e.printStackTrace();}}public void snippetEventHandler(SnippetEvent snippetEvent){String value = snippetEvent.value();if(!Objects.isNull(value) && value.trim().length() > 0) {// Prints output of code evaluationSystem.out.println(value);}// If there are any erros print and exitif(Snippet.Status.REJECTED.equals(snippetEvent.status())){System.out.println("Evaluation failed : "+snippetEvent.snippet().toString()+"\nIgnoring execution of above script");}}private String trimNewlines(String s) {int b = 0;while (b < s.length() && s.charAt(b) == '\n') {++b;}int e = s.length() -1;while (e >= 0 && s.charAt(e) == '\n') {--e;}return s.substring(b, e + 1);}
}

module-info.java

module ex.jshell.extension{   requires jdk.jshell;
}

赶快试用下强大的JShell吧。

来源 | https://urlify.cn/fyiIRr

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