Injector

MixinTestTarget.java

package com.voxelgenesis.test.inject;

import com.voxelgenesis.injector.Inject;
import com.voxelgenesis.injector.Injector;
import com.voxelgenesis.test.TestTarget;

@Injector(TestTarget.class)
public class MixinTestTarget {

    // This injection is replacing the value of the local assignment
    // with a new value. the $( val ) wraps an instruction of arbitrary
    // complexity and denotes that the injection will replace the
    // value of instruction.
    //
    // The injection token wraps the expected starting value of the
    // injection target and the method must have a return type of the
    // correct type.
    //
    // Types are specified as fully qualified names separated by forward
    // slashes '/'. This is because if there is not an import specified
    // (see the next example) then there is no way to determine where the
    // type name ends and a string of field accesses begins.
    @Inject(target = "foo()V", matcher  = "String a = $(\"foo\");"
                                        + "java/lang/System.out.println(a);")
    public String updateFoo() {
        return "bar";
    }
    
    // This injection is an example of inserting new statements into the
    // method. the `$$;` token denotes this type of injection.
    //
    // The locals of the injector are mapped the the correct (or new)
    // locals and the injector statements are inlined directly into the
    // target method.
    //
    // Here the System class is specied in the imports array so that
    // its full name does not need to be included in the matcher every time.
    @Inject(target = "foo()V", matcher  = "String a = \"foo\";"
                                        + "$$;"
                                        + "System.out.println(a);",
           imports = {System.class})
    public void updateFoo2(@Local("a") String a) {
        a = "bar";
    }
    
    // This injection is replacing the condition of the if statement
    // it is able to do this because the injection is performed on
    // the methods statements rather than its bytecode instructions
    // and so it is no problem to add a new conditional jump
    @Inject(target = "foo()V", matcher = "if ($(msg2 != null))")
    public boolean updateBazIf(@Local("msg2") String msg2) {
        return msg2 != null && !msg2.isEmpty();
    }

}

TestTarget.java

package com.voxelgenesis.test;

public class TestTarget {

    public void foo() {
        String msg = "foo";
        System.out.println(msg);
        String msg2 = "";
        if (msg2 != null) {
            System.out.println("baz");
        }
    }

}