如何在Cofoja中使用离线字节码编写器？

Question

I'm trying to do offline instrumentation of my code using Cofoja (contracts for Java). I cannot seem to get the contracts in the compiled class file using the offline bytecode writer (this feature is briefly mentioned in the Invocation section of the GitHub page). I execute the resulting class file and purposely fail a contract. Nothing happens.

Here is my Java code... In my main I simply do something like: return divide(10, 0);

  @Requires("y != 0")
  public static int divide(int x, int y)
  {
    return x / y;
  }

Then I do the following:

I build the .java file via my IDE, Intellij and get the class file.
Then execute the offline bytecode writer like this:

java -Dcom.google.java.contract.classoutput=cofoja -cp cofoja.asm-1.2-20140817.jar com.google.java.contract.core.agent.PreMain JavaTest.class

This results in another "JavaTest.class" file being generated in the "cofoja" directory. However, when I execute it I don't see any contract errors.

Does anyone know the correct steps to use "com.google.java.contract.core.agent.PreMain" to generate class files with contracts weaved in?

Answer 1

Just for future reference, I went and looked at the source code for com.google.java.contract.core.agent.PreMain. It turns out that it expects the contract files and helper files to live in the same place as your regular java class files. Once I include the class files along with the contract files (in the same directory) this started working.
So to recap:

java -d {output_dir} -cp {your_classpath} "-Acom.google.java.contract.classoutput={output_dir}" "-Acom.google.java.contract.classpath={your_classpath}" "-Acom.google.java.contract.sourcepath={your_sources_dir}" -processor com.google.java.contract.core.apt.AnnotationProcessor

to compile java classes and cofoja contract files. Make sure the class files go in the same directory as the cofoja contract files.
Then execute this:

java -Dcom.google.java.contract.classoutput={output_dir} -cp cofoja.asm-1.2-20140817.jar com.google.java.contract.core.agent.PreMain {all .class files separated by spaces}

This command will generate single .class files with contracts built in which you can then compile into a jar file. Note that you need to have a list of all of your original class files as the arguments to the last command and make sure the contract files and helper files are sitting next to the corresponding class file.