java 从数据库获取源码、动态编译、方法调用，someone like u

 @RequestMapping("/test/load")
    @ResponseBody
    public AjaxResult classLoad(@NotBlank String key) throws Exception {
       //    String javaSrc = exampleService.findConfigByKey(key);//从数据库获取以下源码
        String javaSrc = " import com.eos.wxapp.controller.test.Singer;\n" +
                "public class ZBC implements Singer {\n" +
                "    @Override\n" +
                "    public void sing() {\n" +
                "        System.out.println(\"一首凉凉送给你\");\n" +
                "    }\n" +
                "}\n";
        String className = "ZBC";
        try {
            Test.testInvoke(className, javaSrc);
        } catch (ClassNotFoundException | IllegalAccessException
                | InstantiationException | NoSuchMethodException
                | InvocationTargetException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return AjaxResult.success();
    }

 public static void testInvoke(String className, String source) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
        final String SUFFIX = ".java";// 类名后面要跟的后缀
        // 对source进行编译生成class文件存放在Map中，这里用bytecode接收
        Map<String, byte[]> bytecode = DynamicLoader.compile(className + SUFFIX,
                source);
        // 加载class文件到虚拟机中，然后通过反射执行
        @SuppressWarnings("resource")
        DynamicLoader.MemoryClassLoader classLoader = new DynamicLoader.MemoryClassLoader(
                bytecode);
        Class<?> clazz = classLoader.loadClass("ZBC");
        Singer someone = (Singer) clazz.newInstance();
        someone.sing();
    }

import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

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

public class DynamicLoader {

    /**
     * 通过类名和其代码（Java代码字符串），编译得到字节码，，封装于Map中，值得注意的是，
     * 平常类中就编译出来的字节码只有一个类，但是考虑到内部类的情况， 会出现返回类名及其对应类的字节码很多个类名及其字节码，所以用Map封装方便。
     *
     * @param javaName 类名
     * @param javaSrc  Java源码
     * @return map
     */
    public static Map<String, byte[]> compile(String javaName, String javaSrc) {
        // 调用java编译器接口
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager stdManager = compiler
                .getStandardFileManager(null, null, null);

        try (MemoryJavaFileManager manager = new MemoryJavaFileManager(
                stdManager)) {

            @SuppressWarnings("static-access")
            JavaFileObject javaFileObject = manager.makeStringSource(javaName,
                    javaSrc);
            JavaCompiler.CompilationTask task = compiler.getTask(null, manager,
                    null, null, null, Arrays.asList(javaFileObject));
            if (task.call()) {
                return manager.getClassBytes();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 先根据类名在内存中查找是否已存在该类，若不存在则调用 URLClassLoader的 defineClass方法加载该类
     * URLClassLoader的具体作用就是将class文件加载到jvm虚拟机中去
     *
     * @author Administrator
     *
     */
    public static class MemoryClassLoader extends URLClassLoader {
        Map<String, byte[]> classBytes = new HashMap<String, byte[]>();

        public MemoryClassLoader(Map<String, byte[]> classBytes) {
            super(new URL[0], MemoryClassLoader.class.getClassLoader());
            this.classBytes.putAll(classBytes);
        }

        @Override
        protected Class<?> findClass(String name)
                throws ClassNotFoundException {
            byte[] buf = classBytes.get(name);
            if (buf == null) {
                return super.findClass(name);
            }
            classBytes.remove(name);
            return defineClass(name, buf, 0, buf.length);
        }
    }
}

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.Reader;
import java.io.StringReader;
import java.net.URI;
import java.nio.CharBuffer;
import java.util.HashMap;
import java.util.Map;
import javax.tools.FileObject;
import javax.tools.ForwardingJavaFileManager;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;

/**
 * 将编译好的.class文件保存到内存当中，这里的内存也就是map映射当中
 */
@SuppressWarnings("rawtypes")
public final class MemoryJavaFileManager extends ForwardingJavaFileManager {
    private final static String EXT = ".java";// Java源文件的扩展名
    private Map<String, byte[]> classBytes;// 用于存放.class文件的内存

    @SuppressWarnings("unchecked")
    public MemoryJavaFileManager(JavaFileManager fileManager) {
        super(fileManager);
        classBytes = new HashMap<String, byte[]>();
    }

    public Map<String, byte[]> getClassBytes() {
        return classBytes;
    }

    @Override
    public void close() throws IOException {
        classBytes = new HashMap<String, byte[]>();
    }

    @Override
    public void flush() throws IOException {
    }

    /**
     * 一个文件对象，用来表示从string中获取到的source，一下类容是按照jkd给出的例子写的
     */
    private static class StringInputBuffer extends SimpleJavaFileObject {
        // The source code of this "file".
        final String code;

        /**
         * Constructs a new JavaSourceFromString.
         *
         * @param name 此文件对象表示的编译单元的name
         * @param code 此文件对象表示的编译单元source的code
         */
        StringInputBuffer(String name, String code) {
            super(toURI(name), Kind.SOURCE);
            this.code = code;
        }

        @Override
        public CharBuffer getCharContent(boolean ignoreEncodingErrors) {
            return CharBuffer.wrap(code);
        }

        @SuppressWarnings("unused")
        public Reader openReader() {
            return new StringReader(code);
        }
    }

    /**
     * 将Java字节码存储到classBytes映射中的文件对象
     */
    private class ClassOutputBuffer extends SimpleJavaFileObject {
        private String name;

        /**
         * @param name className
         */
        ClassOutputBuffer(String name) {
            super(toURI(name), Kind.CLASS);
            this.name = name;
        }

        @Override
        public OutputStream openOutputStream() {
            return new FilterOutputStream(new ByteArrayOutputStream()) {
                @Override
                public void close() throws IOException {
                    out.close();
                    ByteArrayOutputStream bos = (ByteArrayOutputStream) out;
                    // 这里需要修改
                    classBytes.put(name, bos.toByteArray());
                }
            };
        }
    }

    @Override
    public JavaFileObject getJavaFileForOutput(
            JavaFileManager.Location location, String className,
            JavaFileObject.Kind kind, FileObject sibling) throws IOException {
        if (kind == JavaFileObject.Kind.CLASS) {
            return new ClassOutputBuffer(className);
        } else {
            return super.getJavaFileForOutput(location, className, kind,
                    sibling);
        }
    }

    public static JavaFileObject makeStringSource(String name, String code) {
        return new StringInputBuffer(name, code);
    }

    static URI toURI(String name) {
        File file = new File(name);
        if (file.exists()) {// 如果文件存在，返回他的URI
            return file.toURI();
        } else {
            try {
                final StringBuilder newUri = new StringBuilder();
                newUri.append("mfm:///");
                newUri.append(name.replace('.', '/'));
                if (name.endsWith(EXT)) {
                    newUri.replace(newUri.length() - EXT.length(),
                            newUri.length(), EXT);
                }
                return URI.create(newUri.toString());
            } catch (Exception exp) {
                return URI.create("mfm:///com/sun/script/java/java_source");
            }
        }
    }
}

package com.xx.xx.controller.test;
/**
 * @author Maple
 * @Description:
 * @date 2021/1/2510:42
 */
public interface Singer {
    public void sing();
}