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