为 Lombok 创建自定义注释

Question

我在我的代码中使用了 Lombok 来自动生成 getter 和 setter 代码。我想添加其他个人注释并使用它。

例如，我想添加一个 @Exist 方法来验证列表中是否存在键：

@Getter    @Setter
public class User {

    private String name;
    private List<Integer> keys;

    public boolean existKeys(Integer key) {
        boolean exist = keys.contains(key);
        return exist;
    }
}

创建注释后，我会做类似的事情：

@Getter    @Setter
public class User {

    private String name;
    @Exist
    private List<Integer> keys;
}

Answer 1

一般注意事项

如果您已经在使用 Lombok，则可以添加自定义 Lombok 转换注释和处理程序。

用 @Target(FIELD) 和 @Retention(SOURCE)
定义存在注释
创建一个handler
```
@ProviderFor(JavacAnnotationHandler.class)
public class HandleExists extends JavacAnnotationHandler<Exists>{ ...` 
```
处理您的注释。处理程序 class 包必须以 lombok. 前缀开头。如果除了 javac 之外还需要支持 Eclipse 等，则需要编写更多处理程序来扩展适当的框架 classes.
在处理程序override/implement中的handle()方法通过AST操作生成所需的代码。

您可以将 @Getter 实现作为示例：

注解： Getter.java

处理程序： HandleGetter.java

您还可以查看 sources of other annotations and handlers 以了解如何生成特定代码。

您需要添加对 lombok 的依赖，JDK tools.jar。

部分资源：

lombok-pg project with a source for a bunch of custom lombok annotations, in particular FluentSetter.java, HandleFluentSetter.java / FluentSetterHandler.java
custom transformation
概览
简单 annotation example 有解释。

注意，这里有几点需要考虑

这是一堆需要编写和维护的重要代码。如果您打算使用注释 5-6 次，那是不值得的。
您可能需要通过 lombok 升级来更改注释处理器实现。
lombok 依赖的编译器漏洞也可能被关闭（那么整个 Lombok 项目将发生巨大变化或不复存在；在这种情况下，如果你广泛使用 Lombok，无论如何你都会遇到更严重的问题，即使如果只是为了@Getter).

没有 Lombok 的更复杂的替代方法是使用标准 annotation processing for code generation but, AFAIK, you can't change original classes and must generate/use classes that extend them (unless you'll exploit the same back-door 作为 Lombok 或诉诸代码操作，如 CGLib 或 ASM）。

龙目岛示例

下面是一些工作代码，用于创建我称为 @Contains.

的自定义 Lombok 注释

它只是 javac 实现，没有 Eclipse 等。我想为 Eclipse 或其他 IDE 创建一个类似的处理程序并不难。

它将生成 fieldNameContains() 成员方法，该方法委托给 fieldName.contains().

请注意，该代码只是快速而肮脏（但有效）的示例。对于生产级注释，您将需要处理许多边界条件、检查正确的类型、处理 Lombok 配置等，因为它可以在 lombok 或 lombok-pg 库源中观察到。

示例用法

SomeEnity.java

@Getter
@Setter
public class SomeEntity {

    @NonNull
    @Contains
    private Collection<String> fieldOne = new ArrayList<>();

    @NonNull
    @Contains
    private Collection<String> fieldTwo = new ArrayList<>();

}

SomeEntityTest.java

public class SomeEntityTest {

    @Test
    public void test() {
        SomeEntity entity = new SomeEntity();

        Collection<String> test1 = Arrays.asList(new String[] { "1", "2" });
        entity.setFieldOne(test1);
        assertSame(test1, entity.getFieldOne());

        Collection<String> test2 = new HashSet<String>(Arrays.asList(new String[] { "3", "4" }));
        entity.setFieldTwo(test2);
        assertSame(test2, entity.getFieldTwo());

        assertTrue(entity.fieldOneContains("1"));
        assertTrue(entity.fieldOneContains("2"));
        assertFalse(entity.fieldOneContains("3"));
        assertFalse(entity.fieldOneContains("4"));

        assertFalse(entity.fieldTwoContains("1"));
        assertFalse(entity.fieldTwoContains("2"));
        assertTrue(entity.fieldTwoContains("3"));
        assertTrue(entity.fieldTwoContains("4"));

        try {
            entity.setFieldOne(null);
            fail("exception expected");
        } catch (Exception ex) {
        }

        try {
            entity.setFieldTwo(null);
            fail("exception expected");
        } catch (Exception ex) {
        }

    }
}

注解实现

Contains.java

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.SOURCE)
public @interface Contains {
    Class<?>[] types() default {};
    Class<?>[] excludes() default {};
}

句柄Contains.java

@ProviderFor(JavacAnnotationHandler.class) 
@HandlerPriority(65536) 
@ResolutionResetNeeded 
public class HandleContains extends JavacAnnotationHandler<Contains> {
    
    @Override 
    public void handle(AnnotationValues<Contains> annotation, JCAnnotation ast, JavacNode annotationNode) {
        
        try {
            JavacNode node = annotationNode.up();
            if (node.getKind() != Kind.FIELD) {
                annotationNode.addError("@Contains is allowed only on fields");
                return;
            }
            Name delegateName = annotationNode.toName(node.getName());
            JavacResolution reso = new JavacResolution(annotationNode.getContext());
            JCTree member = node.get();
            if (member.type == null) {
                reso.resolveClassMember(node);
            }
            Type delegateType = member.type;
            if (delegateType instanceof ClassType) {
                ClassType ct = (ClassType) delegateType;
                //TODO validate that this field is a collection type
                // if(!Collection)
                //   annotationNode.addError("@Contains can only be used on collections");
                final String methodName = "contains";
                MethodSig methodSig = getMethodBinding(methodName, ct, annotationNode.getTypesUtil());
                if (methodSig == null) throw new Exception("no method " + methodName + " in " + ct.tsym.name);
                JCMethodDecl methodDecl = createDelegateMethod(methodSig, annotationNode, delegateName);
                injectMethod(node.up(), methodDecl);
            } else {
                annotationNode.addError("@Contains can only use concrete class types");
                return;
            }
        } catch (Exception ex) {
            //ex.printStackTrace();
            annotationNode.addError("@Contains unexpected error: " + ex.getMessage());
        }
        
    }
    
    public JCMethodDecl createDelegateMethod(MethodSig sig, JavacNode annotation, Name delegateName) throws TypeNotConvertibleException {
        
        JavacTreeMaker maker = annotation.getTreeMaker();
        
        com.sun.tools.javac.util.List<JCAnnotation> annotations;
        if (sig.isDeprecated) {
            annotations = com.sun.tools.javac.util.List.of(maker.Annotation(genJavaLangTypeRef(annotation, "Deprecated"), com.sun.tools.javac.util.List.<JCExpression>nil()));
        } else {
            annotations = com.sun.tools.javac.util.List.nil();
        }
        
        JCModifiers mods = maker.Modifiers(PUBLIC, annotations);
        JCExpression returnType = JavacResolution.typeToJCTree((Type) sig.type.getReturnType(), annotation.getAst(), true);
        boolean useReturn = sig.type.getReturnType().getKind() != TypeKind.VOID;
        ListBuffer<JCVariableDecl> params = sig.type.getParameterTypes().isEmpty() ? null : new ListBuffer<JCVariableDecl>();
        ListBuffer<JCExpression> args = sig.type.getParameterTypes().isEmpty() ? null : new ListBuffer<JCExpression>();
        ListBuffer<JCExpression> thrown = sig.type.getThrownTypes().isEmpty() ? null : new ListBuffer<JCExpression>();
        ListBuffer<JCTypeParameter> typeParams = sig.type.getTypeVariables().isEmpty() ? null : new ListBuffer<JCTypeParameter>();
        ListBuffer<JCExpression> typeArgs = sig.type.getTypeVariables().isEmpty() ? null : new ListBuffer<JCExpression>();
        Types types = Types.instance(annotation.getContext());
        
        for (TypeMirror param : sig.type.getTypeVariables()) {
            Name name = ((TypeVar) param).tsym.name;
            
            ListBuffer<JCExpression> bounds = new ListBuffer<JCExpression>();
            for (Type type : types.getBounds((TypeVar) param)) {
                bounds.append(JavacResolution.typeToJCTree(type, annotation.getAst(), true));
            }
            
            typeParams.append(maker.TypeParameter(name, bounds.toList()));
            typeArgs.append(maker.Ident(name));
        }
        
        for (TypeMirror ex : sig.type.getThrownTypes()) {
            thrown.append(JavacResolution.typeToJCTree((Type) ex, annotation.getAst(), true));
        }
        
        int idx = 0;
        String[] paramNames = sig.getParameterNames();
        boolean varargs = sig.elem.isVarArgs();
        for (TypeMirror param : sig.type.getParameterTypes()) {
            long flags = JavacHandlerUtil.addFinalIfNeeded(Flags.PARAMETER, annotation.getContext());
            JCModifiers paramMods = maker.Modifiers(flags);
            Name name = annotation.toName(paramNames[idx++]);
            if (varargs && idx == paramNames.length) {
                paramMods.flags |= VARARGS;
            }
            params.append(maker.VarDef(paramMods, name, JavacResolution.typeToJCTree((Type) param, annotation.getAst(), true), null));
            args.append(maker.Ident(name));
        }
        
        JCExpression accessor = maker.Select(maker.Ident(annotation.toName("this")), delegateName);
        
        JCExpression delegateCall = maker.Apply(toList(typeArgs), maker.Select(accessor, sig.name), toList(args));
        JCStatement body = useReturn ? maker.Return(delegateCall) : maker.Exec(delegateCall);
        JCBlock bodyBlock = maker.Block(0, com.sun.tools.javac.util.List.of(body));
        StringBuilder generatedMethodName = new StringBuilder(delegateName);
        generatedMethodName.append(sig.name.toString());
        generatedMethodName.setCharAt(delegateName.length(), Character.toUpperCase(generatedMethodName.charAt(delegateName.length())));
        return recursiveSetGeneratedBy(maker.MethodDef(mods, annotation.toName(generatedMethodName.toString()), returnType, toList(typeParams), toList(params), toList(thrown), bodyBlock, null), annotation.get(), annotation.getContext());
    }
    
    public static <T> com.sun.tools.javac.util.List<T> toList(ListBuffer<T> collection) {
        return collection == null ? com.sun.tools.javac.util.List.<T>nil() : collection.toList();
    }
    
    public static class MethodSig {
        final Name name;
        final ExecutableType type;
        final boolean isDeprecated;
        final ExecutableElement elem;
        
        MethodSig(Name name, ExecutableType type, boolean isDeprecated, ExecutableElement elem) {
            this.name = name;
            this.type = type;
            this.isDeprecated = isDeprecated;
            this.elem = elem;
        }
        
        String[] getParameterNames() {
            List<? extends VariableElement> paramList = elem.getParameters();
            String[] paramNames = new String[paramList.size()];
            for (int i = 0; i < paramNames.length; i++) {
                paramNames[i] = paramList.get(i).getSimpleName().toString();
            }
            return paramNames;
        }
        
        @Override public String toString() {
            return (isDeprecated ? "@Deprecated " : "") + name + " " + type;
        }
    }
    
    public MethodSig getMethodBinding(String name, ClassType ct, JavacTypes types) {
        MethodSig result = null;
        TypeSymbol tsym = ct.asElement();
        if (tsym == null) throw new IllegalArgumentException("no class");
        
        for (Symbol member : tsym.getEnclosedElements()) {
            if (member.getKind() != ElementKind.METHOD || !name.equals(member.name.toString())) {
                continue;
            }
            if (member.isStatic()) continue;
            if (member.isConstructor()) continue;
            ExecutableElement exElem = (ExecutableElement) member;
            if (!exElem.getModifiers().contains(Modifier.PUBLIC)) continue;
            ExecutableType methodType = (ExecutableType) types.asMemberOf(ct, member);
            boolean isDeprecated = (member.flags() & DEPRECATED) != 0;
            result = new MethodSig(member.name, methodType, isDeprecated, exElem);
        }
        if (result == null) {
            if (ct.supertype_field instanceof ClassType) {
                result = getMethodBinding(name, (ClassType) ct.supertype_field, types);
            }
            if (result == null) {
                if (ct.interfaces_field != null) {
                    for (Type iface : ct.interfaces_field) {
                        if (iface instanceof ClassType) {
                            result = getMethodBinding(name, (ClassType) iface, types);
                            if (result != null) {
                                break;
                            }
                        }
                    }
                }
            }
        }
        return result;
    }
}

为 Lombok 创建自定义注释

Create custom annotation for Lombok

java

annotations

lombok

一般注意事项

龙目岛示例

示例用法

注解实现