Lombok经常用，但是你知道它的原理是什么吗？(二)

public class HelloJvm {

    private String a;
    private String b;

    public static void main(String[] args) {
        int c = 1+2;
        System.out.println(c);
        print();
    }

    private static void print(){

    }
}

int a = 1;
boolean b = false;
char c = 2;

int d = b+c;

@Retention(RetentionPolicy.SOURCE) // 注解只在源码中保留
@Target(ElementType.TYPE) // 用于修饰类
public @interface MySetter {
}

@SupportedSourceVersion(SourceVersion.RELEASE_8)
@SupportedAnnotationTypes("aboutjava.annotion.MySetter")
public class MySetterProcessor extends AbstractProcessor {

    private Messager messager;
    private JavacTrees javacTrees;
    private TreeMaker treeMaker;
    private Names names;

    /**
     * @Description: 1. Message 主要是用来在编译时期打log用的
     *              2. JavacTrees 提供了待处理的抽象语法树
     *              3. TreeMaker 封装了创建AST节点的一些方法
     *              4. Names 提供了创建标识符的方法
     */
    @Override
    public synchronized void init(ProcessingEnvironment processingEnv) {
        super.init(processingEnv);
        this.messager = processingEnv.getMessager();
        this.javacTrees = JavacTrees.instance(processingEnv);
        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) {
        return false;
    }
}

@Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        Set<? extends Element> elementsAnnotatedWith = roundEnv.getElementsAnnotatedWith(MySetter.class);
        elementsAnnotatedWith.forEach(e->{
            JCTree tree = javacTrees.getTree(e);
            tree.accept(new TreeTranslator(){
                @Override
                public void visitClassDef(JCTree.JCClassDecl jcClassDecl) {
                    List<JCTree.JCVariableDecl> jcVariableDeclList = List.nil();
                    // 在抽象树中找出所有的变量
                    for (JCTree jcTree : jcClassDecl.defs){
                        if (jcTree.getKind().equals(Tree.Kind.VARIABLE)){
                            JCTree.JCVariableDecl jcVariableDecl = (JCTree.JCVariableDecl) jcTree;
                            jcVariableDeclList = jcVariableDeclList.append(jcVariableDecl);
                        }
                    }
                    // 对于变量进行生成方法的操作
                    jcVariableDeclList.forEach(jcVariableDecl -> {
                        messager.printMessage(Diagnostic.Kind.NOTE,jcVariableDecl.getName()+"has been processed");
                        jcClassDecl.defs = jcClassDecl.defs.prepend(makeSetterMethodDecl(jcVariableDecl));
                    });
                    super.visitClassDef(jcClassDecl);
                }
            });
        });
        return true;
    }

private JCTree.JCMethodDecl makeSetterMethodDecl(JCTree.JCVariableDecl jcVariableDecl){

    ListBuffer<JCTree.JCStatement> statements = new ListBuffer<>();
    // 生成表达式 例如 this.a = a;
    JCTree.JCExpressionStatement aThis = makeAssignment(treeMaker.Select(treeMaker.Ident(names.fromString("this")), jcVariableDecl.getName()), treeMaker.Ident(jcVariableDecl.getName()));
    statements.append(aThis);
    JCTree.JCBlock block = treeMaker.Block(0, statements.toList());

    // 生成入参
    JCTree.JCVariableDecl param = treeMaker.VarDef(treeMaker.Modifiers(Flags.PARAMETER), jcVariableDecl.getName(), jcVariableDecl.vartype, null);
    List<JCTree.JCVariableDecl> parameters = List.of(param);

    // 生成返回对象
    JCTree.JCExpression methodType = treeMaker.Type(new Type.JCVoidType());
    return treeMaker.MethodDef(treeMaker.Modifiers(Flags.PUBLIC),getNewMethodName(jcVariableDecl.getName()),methodType,List.nil(),parameters,List.nil(),block,null);

}

private Name getNewMethodName(Name name){
    String s = name.toString();
    return names.fromString("set"+s.substring(0,1).toUpperCase()+s.substring(1,name.length()));
}

private JCTree.JCExpressionStatement makeAssignment(JCTree.JCExpression lhs, JCTree.JCExpression rhs) {
    return treeMaker.Exec(
            treeMaker.Assign(
                    lhs,
                    rhs
            )
    );
}

javac -cp $JAVA_HOME/lib/tools.jar aboutjava/annotion/MySetter* -d
javac -processor aboutjava.annotion.MySetterProcessor aboutjava/annotion//TestMySetter.java
javap -p aboutjava/annotion/TestMySetter.class

Compiled from "TestMySetter.java"
public class aboutjava.annotion.TestMySetter {
  private java.lang.String name;
  public void setName(java.lang.String);
  public aboutjava.annotion.TestMySetter();
}