lombok 实现原理(代码)

package com.allens.netty; import com.sun.tools.javac.code.Flags; import com.sun.tools.javac.model.JavacElements; import com.sun.tools.javac.processing.JavacProcessingEnvironment; import com.sun.tools.javac.tree.JCTree; import com.sun.tools.javac.tree.TreeMaker; import com.sun.tools.javac.util.Context; import com.sun.tools.javac.util.List; import com.sun.tools.javac.util.ListBuffer; import com.sun.tools.javac.util.Names; import javax.annotation.processing.AbstractProcessor; import javax.annotation.processing.Messager; import javax.annotation.processing.ProcessingEnvironment; import javax.annotation.processing.RoundEnvironment; import javax.lang.model.SourceVersion; import javax.lang.model.element.Element; import javax.lang.model.element.TypeElement; import javax.tools.Diagnostic; import java.util.Collections; import java.util.HashSet; import java.util.Set; /** * * 参考： * - https://blog.csdn.net/a_zhenzhen/article/details/86065063#TreeMaker.Block * - https://zhuanlan.zhihu.com/p/121031315 * - https://www.cnblogs.com/kanyun/p/11541826.html * - http://www.javaet.com/blog/136.htm * - https://blog.csdn.net/A_zhenzhen/article/details/86065063 * * 编译器修改的语法树，Intellij idea识别不出来，会飘红 * https://stackoverflow.com/questions/15357362/can-i-modify-the-ast-before-the-java-compiler-compiling-the-ast-to-class-file * https://stackoverflow.com/questions/48605327/intellij-cannot-recognize-classes-modified-by-annotation-processor-in-target-cla * * @author yahui.lv lvyahui8@gmail.com * @date 2020/4/8 21:05 */ public class SingletonProcessor extends AbstractProcessor { private Messager messager; private JavacElements elementUtils; private TreeMaker treeMaker; private Names names; @Override public synchronized void init(ProcessingEnvironment processingEnv) { super.init(processingEnv); messager = processingEnv.getMessager(); this.elementUtils = (JavacElements) processingEnv.getElementUtils(); Context context = ((JavacProcessingEnvironment) processingEnv).getContext(); this.treeMaker = TreeMaker.instance(context); this.names = Names.instance(context); } @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) { Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(Singleton.class); messager.printMessage(Diagnostic.Kind.NOTE,"process singleton， size:" + elements.size()); if (! elements.isEmpty()) { for (Element element : elements) { try { JCTree.JCClassDecl classDecl = (JCTree.JCClassDecl) elementUtils.getTree(element); String className = element.getSimpleName().toString(); String staticFieldName = "instance"; messager.printMessage(Diagnostic.Kind.NOTE,"singleton name:" + className); JCTree.JCNewClass jcNewClass = treeMaker.NewClass(null, /* 暂时不支持类型参数 */ List.nil(), treeMaker.Ident(names.fromString(className)), /* 暂时部支持构造函数入参 */ List.nil(), null ); classDecl.defs = classDecl.defs.append(treeMaker.VarDef(treeMaker.Modifiers(Flags.STATIC + Flags.PRIVATE), names.fromString(staticFieldName),treeMaker.Ident(names.fromString(className)),jcNewClass)); ListBuffer<JCTree.JCStatement> methodBlockStatements = new ListBuffer<>(); JCTree.JCReturn jcReturn = treeMaker.Return(treeMaker.Ident(names.fromString(staticFieldName))); methodBlockStatements.add(jcReturn); JCTree.JCBlock methodBlock = treeMaker.Block(0,methodBlockStatements.toList()); classDecl.defs = classDecl.defs.append(treeMaker.MethodDef(treeMaker.Modifiers(Flags.PUBLIC + Flags.STATIC), names.fromString("getInstance"), treeMaker.Ident(names.fromString(className)), List.nil(), List.nil(), List.nil(), methodBlock, null )); } catch (Exception e) { messager.printMessage(Diagnostic.Kind.ERROR,"singleton handle error: " + e.getMessage(),element); } } } return false; } @Override public Set<String> getSupportedAnnotationTypes() { return new HashSet<>(Collections.singletonList(Singleton.class.getCanonicalName())); } @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } }