前言

在学习反射的时候无意间看到：让java变成脚本语言这一文，按照他的思路我完善了一下代码。实现了JAVA的脚本化和动态化，初学者可以像使用python一样在控制窗口内逐行进行编程。

基本功能及使用方法

使用cmd打开javacafe.jar，进入程序

数学运算.png

使用run方法.png

导入其他包.png

异常处理.png

实现

1.使用ToolProvider.getSystemJavaCompiler()获得JavaCompiler类，对输入程序进行动态编译。
2.使用反射机制获得run方法运行程序输出结果。

详细代码

主程入口start.java

package javacafe;

import java.util.Scanner;
import java.util.regex.Pattern;

public class start {
    public static String ImportStr = "";
    public static String CodeStr = "";

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            String code = scanner.nextLine();
            javaCompilerUtil javaCompilerUtil = new javaCompilerUtil();
            // 判断是否为输出语句
            String patterprint = "^print.*$";
            if (Pattern.matches(patterprint, code)) {
                // 合篇编译+输出
                code = code.replace(" ", "");
                code = code.replace("print", "");
                String c1 = "System.out.println(\"";
                //String c2 = code + "=\"+" + code + ");"; 加入括号可以输出print a+b
                String c2 = code + "=\"+(" + code + "));";
                code = CodeStr + c1 + c2;
                javaCompilerUtil.CompileAndRun(ImportStr, code);
            } else if (code.equals("run")) {
                // 合篇编译
                javaCompilerUtil.CompileAndRun(ImportStr, CodeStr);
            } else {
                // 如果是import语句就进行验包
                String pattern = "^import.*$";
                if (Pattern.matches(pattern, code)) {
                    if (javaCompilerUtil.Importable(code)) {
//              System.out.println("引用可以编译");
                        ImportStr += code + ";";
                    }
                } else {
                    // 判断是否符合语法。
                    if (javaCompilerUtil.Compilable(ImportStr, CodeStr + code + ";")) {
//              System.out.println("内容可以编译");
                        CodeStr += code + ";";
                    }
                }
            }
        }
    }
}

编译器工具类javaCompilerUtil.java

package javacafe;

import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
import java.util.List;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.ToolProvider;
import javax.tools.JavaCompiler.CompilationTask;

public class javaCompilerUtil {
    static JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();
    static final List<String> list = Arrays.asList("-d", System.getProperty("user.dir"));
    static final String fileurl = System.getProperty("user.dir") + "/";

    public boolean Compilable(String ipt, String str) {
        try {
            String CLASS_CONTENT = ipt + "public class CompilableClass{public static void run(){##;}}";
            JavaFileObject fileObject = new JavaStringObject("CompilableClass", CLASS_CONTENT.replace("##", str));
            CompilationTask task = javaCompiler.getTask(null, null, null, list, null, Arrays.asList(fileObject));
            return task.call();
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    public boolean Importable(String str) {
        try {
            String CLASS_CONTENT = "##;public class ImportableClass{public static void run(){}}";
            JavaFileObject fileObject = new JavaStringObject("ImportableClass", CLASS_CONTENT.replace("##", str));
            CompilationTask task = javaCompiler.getTask(null, null, null, list, null, Arrays.asList(fileObject));
            return task.call();
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    public void CompileAndRun(String ImportStr, String CodeStr) {
        String CLASS_CONTENT = "public class CompileAndRunClass{public static void run(){##}}";
        String fileStr = ImportStr + CLASS_CONTENT.replace("##", CodeStr);
        JavaFileObject fileObject = new JavaStringObject("CompileAndRunClass", fileStr);
        CompilationTask task = javaCompiler.getTask(null, null, null, list, null, Arrays.asList(fileObject));
        if (!task.call()) {
//              System.out.println("编译失败!");
        } else {
//              System.out.println("编译成功！");
            // 成功以后，就利用反射来执行这个类了
            try {
                URL[] urls = new URL[] { new URL("file:/" + fileurl) };
                URLClassLoader classLoader = new URLClassLoader(urls);
                Class<?> clazz = classLoader.loadClass("CompileAndRunClass");
                Method method = clazz.getDeclaredMethod("run");
                method.invoke(clazz.newInstance());
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

其他工具类JavaStringObject.java

package javacafe;
import java.io.IOException;
import java.net.URI;

import javax.tools.SimpleJavaFileObject;

public class JavaStringObject extends SimpleJavaFileObject {
    private String code;
     
    public JavaStringObject(String name, String code) {
        super(URI.create(name + ".java"), Kind.SOURCE);
        this.code = code;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors)
            throws IOException {
        return code;
    }
}