streamx-co / ExTree

Build AST from the bytecode

ExTree

This library enables Java Lambdas to be represented as objects in the form of expression trees at runtime:

void method(SerializablePredicate<Customer> p) {
  LambdaExpression<Predicate<Customer>> parsed = LambdaExpression.parse(p);
  //Use parsed Expression Tree...
}

making it possible to create type-safe fluent interfaces, i.e. instead of:

Customer obj = ...
obj.property("name").eq("John")

one can write

method<Customer>(obj -> obj.getName() == "John")

in type-safe, refactoring friendly manner. And then the library developer will be able to parse the produced Lambda to the corresponding Expression Tree for analysis.

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ExTree serves as an infrastructure for 2 other projects, allowing you to write SQL or Mongo queries using Java:

• FluentJPA
• FluentMongo

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It's important to say that the library is generic and is not limited to the projects above.

How to write fluent interface with ExTree?

• Suppose you want to reference some class property

public class Fluent<T> {

	// this interface is required to make the lambda Serializable, which removes a need for 
	// jdk.internal.lambda.dumpProxyClasses system property. See below.
	public static interface Property<T, R> extends Function<T, R>, Serializable {
	}

	public Fluent<T> property(Property<T, ?> propertyRef) {
		LambdaExpression<Function<T, ?>> parsed = LambdaExpression
				.parse(propertyRef);
		Expression body = parsed.getBody();
		Expression methodCall = body;
		
		// remove casts
		while (methodCall instanceof UnaryExpression)
			methodCall = ((UnaryExpression) methodCall).getFirst();

		// checks are omitted for brevity
		Member member = ((MemberExpression) ((InvocationExpression) methodCall)
				.getTarget()).getMember();
		
		// use member
		...
		
		return this;
	}
}

• Now your users will be able to write

Fluent<Customer> f = new Fluent<Customer>();
f.property(Customer::getName);

Build instructions (*NIX):

• mkdir $HOME/lambda
• mvn clean install

License

ExTree is distributed under the terms of the LGPL license.

Release instructions

• export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-amd64
• mvn release:clean release:prepare -P release
• mvn release:perform -P release