Saving modified AST in a new file with eclipse plugin

Question

I have a eclipse plugin code to manipulate a class (smcho.Hello) in a project/workspace. I could create a CompilationUnit and did some modifications on it, but I need to save the result in different file to check the differences between the two version.

This is the code how I get the CompilationUnit.

IWorkspaceRoot root = ResourcesPlugin.getWorkspace().getRoot();
IProject project = root.getProject("Hello");
project.open(null);
IJavaProject javaProject = JavaCore.create(project);
IType lwType = javaProject.findType("smcho.Hello");
org.eclipse.jdt.core.ICompilationUnit lwCompilationUnit = lwType.getCompilationUnit();
final ASTParser parser = ASTParser.newParser(AST.JLS3); 
parser.setKind(ASTParser.K_COMPILATION_UNIT);
parser.setSource(lwCompilationUnit);
parser.setResolveBindings(true); // we need bindings later on
CompilationUnit unit = (CompilationUnit) parser.createAST(null /* IProgressMonitor */); 
// modify the unit AST node

How can I save this modified unit into a new file?

Answer 1

You can use an ASTRewriter to do so.

// get the ast rewriter
final ASTRewrite rewriter = ASTRewrite.create(ast);
// get the current document source
final Document document = new Document(unit.getSource());
// compute the edits you have made to the compilation unit
final TextEdit edits = rewriter.rewriteAST();
// apply the edits to the document
edits.apply(document);
// get the new source
String newSource = document.get();
// now write this source to some other file.

Check the link below. This gives insight on how to write the AST changes to the file.

http://www.eclipse.org/articles/article.php?file=Article-JavaCodeManipulation_AST/index.html

Update: This is how i write to the file:

File file = new File(destFile);
FileUtils.writeStringToFile(File file, String newSource) 

Answer 2

This is the code that I could use for saving the rewritten ast into another file. I wonder if there might be simpler way.

Document document = new Document(lwCompilationUnit.getSource());
rewrite.rewriteAST().apply(document);
String source = document.get();
String destFile = "...";
Helper.toFile(source, destFile);

public static void toFile(String source, String outputPath)
{
   try{
          // Create file 
          FileWriter fstream = new FileWriter(outputPath);
          BufferedWriter out = new BufferedWriter(fstream);
          out.write(source);
          //Close the output stream
          out.close();
    }catch (Exception e){//Catch exception if any
          System.err.println("Error: " + e.getMessage());
    }
}