NullPointerException when using Spoon

[hylhp]

Hi, I use spoon 5.5.0 under Ubuntu with jvm7. The experiment I did is:

1. write a CatchProcess following the doc in http://spoon.gforge.inria.fr/first_analysis_processor.html
2. compile it with javac and run it.
   Everything works well.

But if I delete the generated spooned dir and CatchProcess.java, NPE is thrown as following:

Exception in thread "main" java.lang.NullPointerException
	at org.eclipse.jdt.internal.compiler.batch.FileSystem.<init>(FileSystem.java:141)
	at org.eclipse.jdt.internal.compiler.batch.Main.getLibraryAccess(Main.java:3086)
	at spoon.support.compiler.jdt.JDTBatchCompiler.getUnits(JDTBatchCompiler.java:107)
	at spoon.support.compiler.jdt.JDTBasedSpoonCompiler.buildUnits(JDTBasedSpoonCompiler.java:410)
	at spoon.support.compiler.jdt.JDTBasedSpoonCompiler.buildUnitsAndModel(JDTBasedSpoonCompiler.java:372)
	at spoon.support.compiler.jdt.JDTBasedSpoonCompiler.buildSources(JDTBasedSpoonCompiler.java:348)
	at spoon.support.compiler.jdt.JDTBasedSpoonCompiler.build(JDTBasedSpoonCompiler.java:119)
	at spoon.support.compiler.jdt.JDTBasedSpoonCompiler.build(JDTBasedSpoonCompiler.java:102)
	at spoon.Launcher.buildModel(Launcher.java:700)
	at spoon.Launcher.run(Launcher.java:651)

[surli]

I'm not sure to understand your problem here: if you deleted the file CatchProcess.java and you use it in your program it seems natural that you've an error, no? Or do I miss something?

[hylhp]

I compiled CatchProcess.java and got CatchProcess.class.
Then I think we don't need CatchProcess.java to run spoon. Is it right?
I encounter this problem when I tar the generated classes into a jar file and try to run spoon with this jar file.

[surli]

Then I think we don't need CatchProcess.java to run spoon. Is it right?

You're right, you don't need it to run Spoon if it's already compiled.
But if you're trying to pass Spoon sources as input to spoon, then you need all classes, except if you use the specific "no-classpath" mode.

I assume you're using a command line like that to run spoon:
java -classpath /path/to/binary/of/your/processor.jar:spoon-core-5.5.0-jar-with-dependencies.jar spoon.Launcher -i /path/to/src/of/your/project -p fr.inria.gforge.spoon.processors.CatchProcessor

Then what's your input project (-i argument)?

[hylhp]

My input project is MapReduce framework source code (in a different dir from the dir of CatchProcess.java).

At the beginning, I tried to launch spoon inside the main function. But it throws above NPE error.
So I step back again and again to the official example.

How can I launch spoon only with the generated class files?

[surli]

The easiest way is certainly to use the maven plugin: https://github.com/SpoonLabs/spoon-maven-plugin

You can also get the jar-with-dependencies from the latest release: https://github.com/INRIA/spoon/releases/download/spoon-core-5.5.0/spoon-core-5.5.0-jar-with-dependencies.jar and to call it specifying in the classpath, the path of your compiled processor:

java -classpath /path/to/package/of/your/binary/processor/:spoon-core-5.5.0-jar-with-dependencies.jar spoon.Launcher -i /path/to/src/of/your/project -p fr.inria.gforge.spoon.processors.CatchProcessor

[hylhp]

Thanks for the reply.
Now I think spoon also requires processor source file as input. Is it correct?
I use gradle instead of maven.

Another thing is: I try to replace a method parameter (add one more parameter).
In http://spoon.gforge.inria.fr/template_definition.html, it shows an example about how to do such replacement. But the method body also replaces to empty.
How to keep such method body unchanged?

[surli]

I use gradle instead of maven.

There's also a gradle plugin for Spoon: https://github.com/SpoonLabs/spoon-gradle-plugin :)

Now I think spoon also requires processor source file as input. Is it correct?

We assume in our example that you created and installed a maven/gradle project locally containing your processor: basically you create a maven project with your new processor and necessary dependencies, and you locally install it with mvn install. Then you use a dependency to your new module as explained there: https://github.com/SpoonLabs/spoon-gradle-plugin#how-to-add-processors

In http://spoon.gforge.inria.fr/template_definition.html, it shows an example about how to do such replacement. But the method body also replaces to empty.
How to keep such method body unchanged?

You should be able to do it by using the .S() method. Could you give an example of your code?

[hylhp]

Very cool!

My task is to add parameter to existing methods and keep all other things the same.
I push my code to the github: https://github.com/hylhp/Spoon-example
Now, I can add parameter and copy method body. But there are two problems:

1. Hello.java has two classes. After transmission, only the public class exists in the generated java file.
2. How to keep method return type, thrownType the same?

Thanks again for your help.

[surli]

Hello.java has two classes. After transmission, only the public class exists in the generated java file.

Actually you should have another file for the second class in the output. If you want to keep the same CompilationUnit you can use the following option:

[--output-type <output-type>]
        States how to print the processed source code:
        nooutput|classes|compilationunits (default: classes)

with value "compilationunits".

How to keep method return type, thrownType the same?

I did not understand your question there: if I execute your code, currently nothing happens during the substition, I obtain exactly the same print method. What do you want to do there?

[surli]

@hylhp actually you were right: there was a deeply hidden bug in Spoon which occured only when using Spoon in an empty directory (i.e. without any .java files in it).
We fixed it in #1208 and the patch will be integrated in the next release which should be done by the end of the next week.