<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.6</version>
    <scope>provided</scope>
</dependency>
 
 
<plugins>
     <plugin>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-maven-plugin</artifactId>
         <configuration>
             <excludes>
                 <exclude>
                     <groupId>org.projectlombok</groupId>
                     <artifactId>lombok</artifactId>
                 </exclude>
             </excludes>
         </configuration>
     </plugin>
 </plugins>

CompilationTask getTask(Writer out,
                            JavaFileManager fileManager,
                            DiagnosticListener<? super JavaFileObject> diagnosticListener,
                            Iterable<String> options,
                            Iterable<String> classes,
                            Iterable<? extends JavaFileObject> compilationUnits);

public URL getUrl() throws MalformedURLException {
        if (this.url == null) {
            String file = this.rootFile.getFile().toURI() + this.pathFromRoot + "!/";
            file = file.replace("file:////", "file://"); // Fix UNC paths
            // 這里返回的時候 new了一個Handler來處理URL
            this.url = new URL("jar", "", -1, file, new Handler(this));
        }
        return this.url;
    }

@Override
    protected URLConnection openConnection(URL url) throws IOException {
        if (this.jarFile != null && isUrlInJarFile(url, this.jarFile)) {
            return JarURLConnection.get(url, this.jarFile);
        }
        try {
            return JarURLConnection.get(url, getRootJarFileFromUrl(url));
        } catch (Exception ex) {
            return openFallbackConnection(url, ex);
        }
    }

protected Class<?> findClass(final String name) throws ClassNotFoundException
    {
        final Class<?> result;
        try {
            result = AccessController.doPrivileged(
                new PrivilegedExceptionAction<Class<?>>() {
                    public Class<?> run() throws ClassNotFoundException {
                        String path = name.replace('.', '/').concat(".class");
                        // 這里調用URLClassPath的getResource方法
                        Resource res = ucp.getResource(path, false);
                        if (res != null) {
                            try {
                                return defineClass(name, res);
                            } catch (IOException e) {
                                throw new ClassNotFoundException(name, e);
                            } catch (ClassFormatError e2) {
                                if (res.getDataError() != null) {
                                    e2.addSuppressed(res.getDataError());
                                }
                                throw e2;
                            }
                        } else {
                            return null;
                        }
                    }
                }, acc);
        } catch (java.security.PrivilegedActionException pae) {
            throw (ClassNotFoundException) pae.getException();
        }
        if (result == null) {
            throw new ClassNotFoundException(name);
        }
        return result;
    }

Resource getResource(final String name, boolean check) {
            final URL url;
            try {
                url = new URL(base, ParseUtil.encodePath(name, false));
            } catch (MalformedURLException e) {
                throw new IllegalArgumentException("name");
            }
            final URLConnection uc;
            try {
                if (check) {
                    URLClassPath.check(url);
                }
                // 這里就會調用到URLStreamHandler的openConnection方法
                uc = url.openConnection();
                InputStream in = uc.getInputStream();
                if (uc instanceof JarURLConnection) {
                    /* Need to remember the jar file so it can be closed
                     * in a hurry.
                     */
                    JarURLConnection juc = (JarURLConnection)uc;

                    boolean firstLoad = jarfile == null;

                    jarfile = JarLoader.checkJar(juc.getJarFile());

                    if (firstLoad && JarLoadEvent.isEnabled()) {
                        Tooling.notifyEvent(JarLoadEvent.jarLoadEvent(url, jarfile));
                    }
                }
            } catch (Exception e) {
                return null;
            }
            return new Resource() {
                public String getName() { return name; }
                public URL getURL() { return url; }
                public URL getCodeSourceURL() { return base; }
                public InputStream getInputStream() throws IOException {
                    //JarURLConnection的getInputStream方法
                    return uc.getInputStream();
                }
                public int getContentLength() throws IOException {
                    return uc.getContentLength();
                }
            };
        }

public DynamicCompiler(ClassLoader userClassLoader) {
        if (javaCompiler == null) {
            throw new IllegalStateException("Can not load JavaCompiler from javax.tools.ToolProvider#getSystemJavaCompiler(), please confirm the application running in JDK not JRE.");
        }

        standardFileManager = javaCompiler.getStandardFileManager(null, null, null);

        options.add("-Xlint:unchecked");
        options.add("-g");

        List<URL> urlList = new ArrayList<>();
        //添加自定義jar資源
        urlList.addAll(getCustomJarUrl());
        //獲取userClassLoader加載的資源（SpringBoot服務 LaunchedURLClassLoader）
        urlList.addAll(getClassLoaderUrl(userClassLoader));

        // 向上查找父類
        ClassLoader appClassLoader = getAppClassLoader(userClassLoader);

        //DynamicClassLoader同樣繼承URLClassLoader
        dynamicClassLoader = new DynamicClassLoader(urlList.toArray(new URL[0]), appClassLoader);
    }

private List<JavaFileObject> processJar(URL packageFolderURL) {
        List<JavaFileObject> result = new ArrayList<>();
        try {
            String jarUri = packageFolderURL.toExternalForm().substring(0, packageFolderURL.toExternalForm().lastIndexOf("!/"));

            JarURLConnection jarConn = (JarURLConnection) packageFolderURL.openConnection();
            String rootEntryName = jarConn.getEntryName();
            if (StringUtils.isBlank(rootEntryName)){
                return new ArrayList<>();
            }

            int rootEnd = rootEntryName.length() + 1;

            Enumeration<JarEntry> entryEnum = jarConn.getJarFile().entries();
            while (entryEnum.hasMoreElements()) {
                JarEntry jarEntry = entryEnum.nextElement();
                String name = jarEntry.getName();
                if (name.startsWith(rootEntryName) && name.indexOf('/', rootEnd) == -1 && name.endsWith(CLASS_FILE_EXTENSION)) {
                    URI uri = URI.create(jarUri + "!/" + name);
                    String binaryName = name.replaceAll("/", ".");
                    binaryName = binaryName.replaceAll(CLASS_FILE_EXTENSION + "$", "");

                    result.add(new CustomJavaFileObject(binaryName, uri));
                }
            }
        } catch (Exception e) {
            throw new RuntimeException("Wasn't able to open " + packageFolderURL + " as a jar file", e);
        }
        return result;
    }

public Map<String, byte[]> buildGetByteCodes() {

        errors.clear();
        warnings.clear();

        JavaFileManager fileManager = new DynamicJavaFileManager(standardFileManager, dynamicClassLoader);

        DiagnosticCollector<JavaFileObject> collector = new DiagnosticCollector<>();
        JavaCompiler.CompilationTask task = javaCompiler.getTask(null, fileManager, collector, options, null, compilationUnits);

        try {

            if (!compilationUnits.isEmpty()) {
                boolean result = task.call();

                if (!result || collector.getDiagnostics().size() > 0) {

                    for (Diagnostic<? extends JavaFileObject> diagnostic : collector.getDiagnostics()) {
                        switch (diagnostic.getKind()) {
                            case NOTE:
                            case MANDATORY_WARNING:
                            case WARNING:
                                warnings.add(diagnostic);
                                break;
                            case OTHER:
                            case ERROR:
                            default:
                                errors.add(diagnostic);
                                break;
                        }

                    }
                    if (!errors.isEmpty()) {
                        return new HashMap<>();
                    }
                }
            }

            return dynamicClassLoader.getByteCodes();
        } catch (ClassFormatError e) {
            throw new DynamicCompilerException(e, errors);
        } finally {
            compilationUnits.clear();
        }
    }

@Override
    public JavaFileObject getJavaFileForOutput(Location location, String className, JavaFileObject.Kind kind, FileObject sibling) {

        if (JavaFileObject.Kind.SOURCE.equals(kind)) {
            // 源碼
            for (StringSource stringSource : this.sourceCodes) {
                if (stringSource.getClassName().equals(className)) {
                    return stringSource;
                }
            }

            StringSource stringSource = new StringSource(className);
            sourceCodes.add(stringSource);
            //這里可以存一下動態生成的源代碼，編譯完成后輸出到文件夾
            //            classLoader.registerCompiledSource(stringSource);
            return stringSource;

        } else {
            // 字節碼
            for (MemoryByteCode byteCode : this.byteCodes) {
                if (byteCode.getClassName().equals(className)) {
                    return byteCode;
                }
            }

            MemoryByteCode innerClass = new MemoryByteCode(className);
            byteCodes.add(innerClass);
            classLoader.registerCompiledSource(innerClass);
            return innerClass;
        }
    }