Trugger is a framework that helps you write code that anyone can read. The idea is to provide a set of fluent interfaces to deal with operations related to reflection (such as creating proxies, reflecting members, instantiating objects).

Trugger is intended to be a base for creating infrastructure code. While it is not an IoC container, for example, it could be a part of the core of an IoC container.

What a hell does the name trugger mean?

When I was learning java, I choosed “Atatec” (Ataxexe Technology) to be the name of my fictitious company and then I sent a message to my friend Ives:


And the response was:


When I asked him why he came up with this, he said:

Isn’t that the name of that special kick in Street Fighter?

The special kick mentioned is the Tatsumaki Senpuu Kyaku and Ken says something like “atatec trugger” (at least in Portuguese) when he does the kick. So the name Trugger became my first choice when I start to write this framework.

How To Use

Just put the jar file on your classpath and you’re done. No dependencies are required by Trugger at runtime. If you prefer some build system like Gradle or Maven, trugger is in now in Maven Central repository:

groupId: tools.devnull

artifactId: trugger

How To Build

Just make sure you have Maven and execute the mvn install command.

How To Contribute

Just fork the project, do some stuff and send me a pull request. You can also fire an issue or tell your friends to use Trugger.


The Reflection module was the first one to show up in Trugger, it allows simple and much less verbose use of the Reflection API to reflect constructors, methods, fields and generic type declarations.

The base class of this module is Reflection and you will find a nice fluent interface there with the methods reflect, invoke and handle.



Reflecting a field is done with the code reflect().field(field name). You can also apply a filter by using the method filter and the target class (or object) by using the method from. If you need a recursive search through the entire target class hierarchy, just use the method deep.

Here is some examples (assuming a static import):

Field value = reflect().field("value").from(String.class).result();

Field name = reflect().field("name").deep().in(MyClass.class).result();

Field id = reflect().field("id")
    .filter(field -> field.getType().equals(Long.class))

The filter method receive a java.util.function.Predicate to stay in touch with Java 8.

And what about the #result?

The .result() is needed because the selection return allows to chain some actions:

String value = reflect()


This allows more readability, at the cost of one more method invocation.


If you need to reflect a set of fields, use the reflect().fields(). The same features of a single reflect is available here.

List<Field> stringFields = reflect().fields()
    .filter(field -> field.getType().equals(String.class))


There are some builtin predicates in the class FieldPredicates.

List<Field> stringFields = reflect().fields()
    .filter(type(String.class)) // a static import

Handling Values

A field can have its value manipulated through the method Reflection#handle. It will create a handler to set and get the field’s value without the verbosity of the Reflection API. To handle static fields, you can call the handler methods directly:

String value = handle(field).getValue();
handle(field).setValue("new value");

For instance fields, just specify an instance using the method on:

String value = handle(field).on(instance).getValue();
handle(field).on(instance).setValue("new value");



To reflect a constructor, use reflect().constructor() and specify the parameter types and optionally a filter. If the class has only one constructor, it can be reflected without supplying the parameter types.

Constructor constructor = reflect()

Constructor constructor = reflect().constructor()

Constructor constructor = reflect().constructor()
  .filter(c -> c.isAnnotationPresent(SomeAnnotation.class))

Constructor constructor = reflect().constructor().from(MyClass.class).result();

MyClass obj = reflect().constructor().from(MyClass.class).and(instantiate(parameter));


A set of constructors can be reflected by using reflect().constructors(). As in fields, the features in single reflection are present in multiple reflection.

List<Constructor> constructors = reflect().constructors().from(MyClass.class);

List<Constructor> constructors = reflect().constructors()
  .filter(c -> c.getParameterCount() == 2)

Note that in multiple selection you cannot specify the parameter types directly in the fluent interface (for obvious reasons).


A few useful predicates are included in the class ConstructorPredicates.

List<Constructor> constructors = reflect().constructors()
  .filter(annotated()) // a static import


To invoke a constructor you need an Invoker. The method Reflection#invoke returns a Invoker for a constructor. Specify the parameters and the constructor will be invoked.

Constructor c = reflect().constructor()
String name = invoke(c).withArgs("Trugger");



To reflect a single method, just pass it name to Reflection#method. Filtering is allowed and you can specify parameter types too.

Method toString = reflect().method("toString").from(Object.class).result();

Method remove = reflect().method("remove")
  .withParameters(Object.class, Object.class)

Method someMethod = reflect().method("foo")
  .filter(method -> method.isAnnotationPresent(PostConstruct.class))


As in field reflection, you can do a deep search with deep.

Method toString = reflect().method("toString").deep().from(MyClass.class).result();


A set of methods can be reflected by using Reflection#methods:

List<Method> methods = reflect().methods().from(Object.class);

Deep search and filtering are also supported:

List<Method> methods = reflect().methods()
  .filter(method -> method.isAnnotationPresent(PostConstruct.class)


A set of predicates to deal with methods is in MethodPredicates:

List<Method> methods = reflect().methods()
  .filter(annotatedWith(PostConstruct.class)) // a static import


To invoke a method, use the Invoker returned by Reflection#invoke. Instance methods needs an instance provided using the method on:

Method toString = reflect().method("toString").on(String.class);
invoke(toString).on("A string").withoutArgs();

Static methods don’t need it:

Method parseInt = reflect().method("parseInt")
int number = invoke(parseInt).withArgs("10");

// alternatively
int number = reflect().method("parseInt")

Generic Type

Generic declarations in a class are present in the bytecode. Trugger can reflect them by using the method genericType. Suppose we have this interface:

public interface Repository<T> {
  // ... some useful methods here

A generic base implementation can use that T:

public class BaseRepository<T> {

  private final Class<T> type;

  protected BaseRepository() {
    this.type = reflect().genericType("T").of(this);

The constructor was declared protected to warn that this will only work for subclasses (it is a Java limitation). A workaround to use this trick in a variable-like way is by declaring an anonymous class:

Repository<MyType> repo = new BaseRepository<MyType>(){};

This is an ugly solution, but works. You can also use a subclass as well, it’s not too ugly, but can lead to a tons of subclasses in your application.

Proxy Creation

A proxy object is created using a interception handler and optionally a fail handler. The DSL exposed starts at Interception with the method intercept and lets you define one or more interfaces to intercept. Additionally, you can set a target and its interfaces will be used. After the behaviour specification, use the method proxy to create the proxy instance.

SomeInterface proxy = Interception.intercept(SomeInterface.class)
  .onCall(context -> logger.info("method intercepted: " + context.method())


The interception logic happens in the handler passed through the method onCall. The handler receives a context, which contains all information about the intercepted method. A fail handler can also be set using the method onFail.

SomeInterface proxy = Interception.intercept(SomeInterface.class)
  // sets a target to delegate the call using the context object
  // delegates the call to the target (this is the default behaviour)
  .onCall(context -> context.invoke())
  // handles any error occurred
  .onFail((context, throwable) -> handleTheFail(throwable))


The fail handler has access to the context so you can delegate the method to the target again (if a timeout occurs, for example).

The Interception Context

The interception context holds everything related to the method interception, included:

  • The arguments passed
  • The method intercepted
  • The declared method intercepted in the target instance
  • The proxy instance
  • The target instance (may be null if not specified when creating the proxy)

The context can be used to delegate the method call to the target (using invoke) or to another instance (using invokeOn). The declared method intercepted can be retrieve by using targetMethod.

Elements of an Object

What is an Element?

An element is any value that an object holds. It may be accessible through a field, invoking a method (a getter or a setter) or even a specific way like the Map#get method.

A basic element in Trugger is a Property or a Field. Trugger tries to find a getter and a setter method for the element name and a field with the same name. This allows manipulate private fields and properties in the same way without bothering you with the way of handling the value.

Obtaining an Element

An element is obtained using the method element in Elements. The same features of a field reflection is here with the addition of getting an element without specifying a name. A set of predicates are present in ElementPredicates.

Element value = element("value").from(MyClass.class).result();

Element id = element()
  .filter(annotatedWith(Id.class)) // static import

List<Element> strings = elements()
  .filter(type(String.class) // static import

Copying Elements

The elements of an object can be copied to another object, even if they are from different types. The DSL starts at the method copy:


This will copy every element. To restrict the copy to non null values, use the notNull method:


You can also apply a function to transform the values before assigning them to the target object (useful when copying values to a different type of object).

  .map(copy -> copy.value().toString())

To filter the elements to copy, just give a selector to the copy method:


Or filter the copy directly using filter

  .filter(copy -> copy.dest().isAnnotationPresent(MyAnnotation.class))

Nested Elements

Nested elements are supported using a ”.” to separate the elements:

Element element = element("address.street").from(Customer.class).result();

value = element.from(customer).getValue();

You can use any level of nesting:

Element element = element("customer.address.street").from(Response.class).result();

value = element.from(response).getValue();

Custom Elements

Some classes have a custom definition of elements. A Map has their keys as elements, an Array has their indexes as elements an so on. Elements are found by an element finder (a class that implements Finder<Element>) and you can write a custom element finder and register it using the registry available through the method Elements#registry.

Trugger has custom element finders for a set of java core classes:

  • Map: keys are used as the elements
  • ResourceBundle: keys are used as the elements
  • Properties: keys are used as the elements
  • ResultSet: the column names are used as the elements
  • Annotation: the methods as used as elements
  • List: indexes are used as the elements (and also two special names, first and last)
  • Arrays: indexes are used as the elements (and also two special names, first and last)

It is important to have clear that since this elements are instance specific, the elements should be queried by passing an instance instead of a class for the method from or an empty list will be returned. For a single elements, you may pass a class or an instance but using an instance is better because you can call the handling methods directly.

You can also use this custom element finders to copy elements easily:

// this will copy every element from the result set to the instance


Context Factories

If you need a lightweight component to invoke a constructor with a predicate based logic to resolve the parameter values, you can use the ContextFactory.

A ContextFactory is a factory that maps a predicate that evaluates parameters to an object or supplier. After creating a ContextFactory, you can manipulate the context through the #context method and create an object with the create method. A set of predicates can be found in ParameterPredicates class.

ContextFactory factory = new ContextFactory();
  //static imports
  .use(parameter ->
  .use(() -> availableWorker())

The above factory will:

  1. use myImplementation for any parameter of the type MyInterface
  2. use someObject for any parameter named “component”
  3. use the return of resolve with the annotation MyAnnotation for any parameter annotated with MyAnnotation
  4. use the return of availableWorker to any parameter of type MyWorker

These steps will be done with every public constructor of a type, if a constructor has one parameter that cannot be resolved to an object, then the next constructor will be used and if there is no more constructors to use, an exception is thrown.

Component Factories

Component factories allows creating components defined by annotations. Suppose you have:

public @interface ComponentClass {

  Class<? extends Component> value();


public @interface MyComponent {

  String name();


//inside a class

@MyComponent(name = "myName")
private String aField;

The annotation in aField can be used to create an instance of MyComponentImplementation. The context used to create any components are:

  1. Every property of the annotation with their specific types (in that case, the property name with the value “myName” to a parameter named name and of type String)
  2. The annotation itself with its type (in that case, the MyComponent annotation to the type MyComponent)

Since the annotation is used as the context, you can have a constructor in the component implementation that receives the annotation instead of its properties. This is useful if you don’t want to compile your code with -parameters parameter.

This behaviour is completely replaceable by using the method configureContextWith. To add behaviour to the default one, compose the ComponentFactory#defaults with your behaviour:

    (context, annotation) -> yourConfigurations

To instantiate a component, just use a code like this one:

ComponentFactory<ComponentClass, Component> factory =
  new ComponentFactory(ComponentClass.class);

// get the annotation from the field

Component component = factory.create(annotation);

Alternatively, you can get a list of components by passing an AnnotatedElement to the method #createAll:

Element = Elements.element("aField").from(myObject).result();
List<Component> components = factory.createAll(element);

Or creating a single one by passing an AnnotatedElement to the method #create:

Element = Elements.element("aField").from(myObject).result();
Component component = factory.create(element);


How To Implement the Fluent Interfaces

The fluent interfaces are always defined through java interfaces and may be customized by your own implementation. Trugger uses a ServiceLoader to load a factory that knows the implementations to instantiate, so you can override the implementation of any fluent interface by defining a file in your META-INF/services directory with the factory implementation.

The factory interfaces that can be customized are listed bellow:

  • ElementFactory: used for selecting elements
  • ReflectionFactory: used for reflection in general
  • InterceptorFactory: used for method interception