文章目录

• 写在前面
• • 1、Java Compiler
  • • 1.1、java文件编译成class文件
    • • run 编译
      • exec 执行指令
    • 1.2、字符串编译成class文件
    • 1.3、工具类

写在前面

Java Compiler 可以动态执行一段字符串形式的java代码，或手动编译java文件。

1、Java Compiler

1.1、java文件编译成class文件

run 编译

D:\Test.java 文件内容：

public class Test {public static void main(String[] args) {int i = 0;System.out.println("test run "+i);}
}

把java文件编译成class文件

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();int result = compiler.run(null, null, null, "D:\\Test.java");   // 在 D:\\Test.java 同目录下，会出现Test.class文件System.out.println(result == 0 ? "编译成功" : "编译失败");

exec 执行指令

exec 执行指令，等同于在cmd中输入指令

        // 执行java命令,空参数,所在文件夹Process process = Runtime.getRuntime().exec("java Test", null, new File("F:\\demo\\"));BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));String str;while ((str = bufferedReader.readLine()) != null) {System.out.println(str);    // 这里打印的是控制台输出的}

如上代码，等同于在cmd输入：java Test

1.2、字符串编译成class文件

新建类 StringObject，代表字符串java对象内容

package com.kaka;import javax.tools.SimpleJavaFileObject;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;// 必须继承自SimpleJavaFileObject 
public class StringObject extends SimpleJavaFileObject {private String content = null;protected StringObject(String className, String contents) throws URISyntaxException {super(new URI(className), Kind.SOURCE);this.content = contents;}@Overridepublic CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {return content;}
}

编译java字符串

package com.kaka;import javax.tools.*;
import java.net.URISyntaxException;
import java.util.Collections;public class Test01 {public static void main(String[] args) throws URISyntaxException {// 要编译的字符串,这个字符串必须是一个类String contents = "package com.kaka;" +"class Test {\n" +"    public static void main(String[] args) {\n" +"\tint i = 0;\n" +"        System.out.println(\"测试运行 \"+i);\n" +"    }\n" +"}";JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();StandardJavaFileManager standardJavaFileManager = javaCompiler.getStandardFileManager(null, null, null);JavaFileObject testFile = new StringObject("com.kaka.Test", contents);JavaCompiler.CompilationTask task = javaCompiler.getTask(null, standardJavaFileManager, null, null, null, Collections.singletonList(testFile));if(task.call()){System.out.println("success");}else{System.out.println("failure!");}}
}

1.3、工具类

将1.1和1.2总结为一个工具类

package com;import javax.tools.*;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URI;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;public class JavaCodeUtil {/** java字符串代码，转为class文件 **/public static String codeToClass(String code,String compilePath) {String className = getClassNameFromCode(code);JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();StandardJavaFileManager fileManager = javaCompiler.getStandardFileManager(null, null, null);JavaFileObject stringObject = new StringObject(className, code);// compilePath 指定编译的class文件的路径List options = Arrays.asList("-d", compilePath);JavaCompiler.CompilationTask task = javaCompiler.getTask(null, fileManager, null, options, null, Collections.singletonList(stringObject));if(task.call()){// 从code第一行读出包名String packageName = getPackageNameInFirstLine(code);String classFileName = className + "." + "class";return compilePath + "/" +  packageName + "/" + classFileName;}else{return null;}}public static String javaToClass(String fileName,String compilePath) throws IOException {JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();StandardJavaFileManager fileManager = javaCompiler.getStandardFileManager(null, null, null);Iterable fileObjects = fileManager.getJavaFileObjects(fileName);// compilePath 指定编译的class文件的路径List options = Arrays.asList("-d", compilePath);JavaCompiler.CompilationTask task = javaCompiler.getTask(null, fileManager, null, options, null, fileObjects);if(task.call()){// 从文件第一行读包名File sourceFile = new File(fileName);BufferedReader bufferedReader = new BufferedReader(new FileReader(sourceFile));String line;while ((line = bufferedReader.readLine()) != null) {if (line.startsWith("package")) {break;}}String packageName = line;packageName = packageName.replaceAll("package", "").trim().replaceAll("\\.", "/");packageName = packageName.substring(0, packageName.length() - 1);// 获取类名（这里简单处理, 默认文件名与类名相同）String sourceFileName = sourceFile.getName();String[] split = sourceFileName.split("\\.");String simpleClassName = split[0] + "." + "class";return compilePath + "/" +  packageName + "/" + simpleClassName;}else{return null;}}public static class StringObject extends SimpleJavaFileObject {private final String content;public StringObject(String className, String contents) {super(URI.create(className), Kind.SOURCE);this.content = contents;}@Overridepublic CharSequence getCharContent(boolean ignoreEncodingErrors){return content;}}/** 根据java文件第一行获取包名 */public static String getPackageNameInFirstLine(String code){return code.substring(0,code.indexOf(";")).replace("package ", "").replaceAll("\\.", "/");}/** 从java String字符串中获取类名 */public static String getClassNameFromCode(String code){int classBlank = code.indexOf("class ")+6;String className = code.substring(classBlank);int nextBlank = className.indexOf(" ");className = className.substring(0,nextBlank);if(className.contains("{")){int i = className.indexOf("{");className = className.substring(0,i);}return className;}/** 获取项目根目录 */public static String getProjectPath() {String path = JavaCodeUtil.class.getProtectionDomain().getCodeSource().getLocation().getPath();if (System.getProperty("os.name").contains("dows")) {path = path.substring(1);}if (path.contains("jar")) {path = path.substring(0, path.lastIndexOf(".")).substring(0, path.lastIndexOf("/"));return path;} else {return path.replace("target/classes/", "");}}
}

测试使用JavaCodeUtil

    public static void main(String[] args) throws ClassNotFoundException {// java代码String contents = "package com.kaka;\n" +"class Test02 {\n" +"    public static void main(String[] args) {\n" +"\tint i = 0;\n" +"        System.out.println(\"这是Test02的main方法 \"+i);\n" +"    }\n" +"   public void getiii(){}\n" +"}";// 把字符串编译成class文件JavaCodeUtil.codeToClass(contents,getProjectPath()+"target/classes");// 加载这个calss文件Class aClass = Class.forName("com.kaka.Test02");// 获取Test02中的方法Method[] methods = aClass.getMethods();for (Method method : methods) {System.out.println(method.getName());}}