Create custom annotation for Lombok
General Considerations
If you are already using Lombok, you can add custom Lombok transformation annotation and handler.
Define Exists annotation with
@Target(FIELD)and@Retention(SOURCE)Create a handler
@ProviderFor(JavacAnnotationHandler.class)
public class HandleExists extends JavacAnnotationHandler<Exists>{ ...`to process your annotation. Handler class package must start with the
lombok.prefix. If you need to support Eclipse, etc. in addition to javac, you'll need to write more handlers extending appropriate framework classes.In the handler override/implement the
handle()method to generate the required code through AST manipulation.
You can take as a sample the @Getter implementation:
Annotation:
Getter.java
Handler:
HandleGetter.java
You can also look into sources of other annotations and handlers to see how to generate particular code.
You'll need to add dependencies on lombok, JDK tools.jar.
Some resources:
The lombok-pg project with a source for a bunch of custom lombok annotations, in particular FluentSetter.java, HandleFluentSetter.java / FluentSetterHandler.java
An overview of a custom transformation
Simple annotation example with explanations.
Note, there are some points to consider here
- This is a bunch of non-trivial code to write and maintain. If you plan to use annotation 5-6 times it is just not worth it.
- You may need to change your annotation processor implementation with lombok upgrades.
- The hole in compiler that lombok relies on also may be closed (then the whole Lombok project will change dramatically or cease to exist; in this case you'll have a more serious problem anyway if you use Lombok extensively, even if just for @Getter).
A more complex alternative without Lombok is to use standard 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 as Lombok or resort to a code manipulation like CGLib or ASM).
Lombok Example
Below is some working code to create custom Lombok annotation that I've called @Contains.
It is javac implementation only, no Eclipse, etc. I guess it will be not hard to create a similar handler for Eclipse or other IDE.
It will generate fieldNameContains() member method which is delegated to the fieldName.contains().
Note, the code is just quick and dirty (but working) sample. For production grade annotation, you will need to handle many boundary conditions, check correct types, handle Lombok configuration and so on, as it can be observed in lombok or lombok-pg library sources.
Sample usage
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) {
}
}
}
Annotation Implementaiton
Contains.java
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.SOURCE)
public @interface Contains {
Class<?>[] types() default {};
Class<?>[] excludes() default {};
}
HandleContains.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;
}
}
Writing custom Lombok Annotation handlers
In the meantime Reinier Zwitserloot created a new git-branch sclExpansionUpdate, that contains an updated version of the ShadowClassLoader:
ShadowClassLoader is now friendlier to trying to extend lombok.
Your (separate) jar/dir should have a file named
META-INF/ShadowClassLoader. This file should contain the string
'lombok'. If you have that, any classes in that jar/dir will be loaded
in the same space as lombok classes. You can also rename the class
files to .SCL.lombok to avoid other loaders from finding them.
I guess this did not yet make it into the main branch because it certainly has not been tested that much - I just tried it out for myself and it contains a little bug that prevents loading the required META-INF/services from extensions. To fix it you should replace two method calls to partOfShadow with inOwnBase:
[... line 443]
Enumeration<URL> sec = super.getResources(name);
while (sec.hasMoreElements()) {
URL item = sec.nextElement();
if (!inOwnBase(item, name)) vector.add(item); // <<-- HERE
}
if (altName != null) {
Enumeration<URL> tern = super.getResources(altName);
while (tern.hasMoreElements()) {
URL item = tern.nextElement();
if (!inOwnBase(item, altName)) vector.add(item); // <<-- AND HERE
}
}
I tested it with the above fix and it seems to work fine (not tested much though).
On a side note: with this new extension mechanism, it is now finally also possible to have the extensions annotation handlers and annotations in a different namespace than "lombok" - nice!
Create Custom annotation which declares and initiates a Object
You can create CGLIB proxy which extends classes annotated with @Test and you can add the property to the proxy. But I don't think it will serve any purpose. Here is the sample code which you use for the starter.
First get list of classes annotated with Test
Reflections reflections = new Reflections ("com.demo");
Set<Class<?>> testClasses = reflections.getTypesAnnotatedWith(Test.class);
Then create a proxy of these classes using CGLIB and add student property to it.
for (Class<?> test : testClasses) {
BeanGenerator beanGenerator = new BeanGenerator ();
beanGenerator.setSuperclass (test);
beanGenerator.addProperty("student", Student.class);
Object myBean = (test) beanGenerator.create();
Method setter = myBean.getClass().getMethod("setStudent", Student.class);
setter.invoke(myBean, new Student());
}
Maven dependencies:
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.2.4</version>
</dependency>
<dependency>
<groupId>org.reflections</groupId>
<artifactId>reflections</artifactId>
<version>0.9.11</version>
</dependency>
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