The Launcher class

The Spoon Launcher (JavaDoc) is used to create the AST model of a project. It can be as short as:

CtClass l = Launcher.parseClass("class A { void m() { System.out.println(\"yeah\");} }");

Or with a plain object:

Launcher launcher = new Launcher();

// path can be a folder or a file
// addInputResource can be called several times


CtModel model = launcher.getModel();

Pretty-printing modes

Autoimport Spoon can pretty-print code where all classes and methods are fully-qualified. This is not readable for humans but enables fast compilation and is useful when name collisions happen.


The autoimport mode computes the required imports, add the imports in the pretty-printed files, and writes class names unqualified (w/o package names):

// if true, the pretty-printed code is readable without fully-qualified names

Sniper mode By default, when pretty-printing, Spoon reformats the code according to its own formatting rules.

The sniper mode enables to rewrite only the transformed AST elements, so that the rest of the code is printed identically to the origin version. This is useful to get small diffs after automated refactoring.

launcher.getEnvironment().setPrettyPrinterCreator(() -> {
   return new SniperJavaPrettyPrinter(launcher.getEnvironment());

The MavenLauncher class

The Spoon MavenLauncher (JavaDoc) is used to create the AST model of a Maven project. It automatically infers the list of source folders and the dependencies from the pom.xml file. This Launcher handles multi-module Maven projects.

// the second parameter can be APP_SOURCE / TEST_SOURCE / ALL_SOURCE
MavenLauncher launcher = new MavenLauncher("<path_to_maven_project>", MavenLauncher.SOURCE_TYPE.APP_SOURCE);
CtModel model = launcher.getModel();

// list all packages of the model
for(CtPackage p : model.getAllPackages()) {
  System.out.println("package: "+p.getQualifiedName());
// list all classes of the model
for(CtType<?> s : model.getAllTypes()) {
  System.out.println("class: "+s.getQualifiedName());

Note that by default, MavenLauncher relies on an existing local maven binary to build the project's classpath. But a constructor allowing the user to skip this step and to provide a custom classpath is available. java MavenLauncher launcher = new MavenLauncher("<path_to_maven_project>", MavenLauncher.SOURCE_TYPE.APP_SOURCE, new String[] { "/home/user/.m2/repository/org/my/jar/1.0/org-my-jar-1.0.jar" } ); launcher.buildModel(); CtModel model = launcher.getModel(); To avoid invoking maven over and over to build a classpath that has not changed, it is stored in a file spoon.classpath.tmp (or depending on the scope spoon.classpath-app.tmp or spoon.classpath-test.tmp) in the same folder as the pom.xml. This classpath will be refreshed is the file is deleted or if it has not been modified since 1h.

The JarLauncher class

The Spoon JarLauncher (JavaDoc) is used to create the AST model from a jar. It automatically decompiles class files contained in the jar and analyzes them. If a pom file corresponding to the jar is provided, it will be used to build the classpath containing all dependencies.

//More constructors are available, check the JavaDOc for more information.
JarLauncher launcher = JarLauncher("<path_to_jar>", "<path_to_output_src_dir>", "<path_to_pom>");
CtModel model = launcher.getModel();

Note that the default decompiler CFR can be changed by providing an instance implementing spoon.decompiler.Decompiler as a parameter.

JarLauncher launcher = new JarLauncher("<path_to_jar>", "<path_to_output_src_dir>", "<path_to_pom>", new Decompiler() {
    public void decompile(String jarPath) {
        //Custom decompiler call

Spoon provides two out of the shelf decompilers, CFR by default, and Fernflower. You can use the later like this: java JarLauncher launcher = new JarLauncher("<path_to_jar>", "<path_to_output_src_dir>", "<path_to_pom>", new FernflowerDecompiler(new File("<path_to_output_src_dir>/src/main/java")));

:warning: The JarLauncher feature (and all features relying on decompilation) are not included in spoon-core but in spoon-decompiler. If you want to use them you should declare a dependency to spoon-decompiler.

About the classpath

Spoon analyzes source code. However, this source code may refer to libraries (as a field, parameter, or method return type). There are two cases:

  • Full classpath: all dependencies are in the JVM classpath or are given to the Laucher with launcher.getEnvironment().setSourceClasspath("<classpath_project>"); (optional)
  • No classpath: some dependencies are unknown and launcher.getEnvironment().setNoClasspath(true) is set.

This has a direct impact on Spoon references. When you're consider a reference object (say, a TypeReference), there are three cases:

  • Case 1 (code available as source code): the reference points to a code element for which the source code is present. In this case, reference.getDeclaration() returns this code element (e.g. TypeReference.getDeclaration returns the CtType representing the given java file). reference.getTypeDeclaration() is identical to reference.getDeclaration().
  • Case 2 (code available as binary in the classpath): the reference points to a code element for which the source code is NOT present, but for which the binary class is in the classpath (either the JVM classpath or the --source-classpath argument). In this case, reference.getDeclaration() returns null and reference.getTypeDeclaration returns a partial CtType built using runtime reflection. Those objects built using runtime reflection are called shadow objects; and you can identify them with method isShadow. (This also holds for getFieldDeclaration and getExecutableDeclaration)
  • Case 3 (code not available, aka noclasspath): the reference points to a code element for which the source code is NOT present, but for which the binary class is NOT in the classpath. This is called in Spoon the noclasspath mode. In this case, both reference.getDeclaration() and reference.getTypeDeclaration() return null. (This also holds for getFieldDeclaration and getExecutableDeclaration)

Declaring the dependency to Spoon




compile 'fr.inria.gforge.spoon:spoon-core:7.6.0-beta-4'

Incremental Launcher

IncrementalLauncher (JavaDoc) allows cache AST and compiled classes. Any spoon analysis can then be restarted from where it stopped instead of restarting from scratch.

final File cache = new File("<path_to_cache>");
Set<File> inputResources = Collections.singleton(new File("<path_to_sources>"));
Set<String> sourceClasspath = Collections.emptySet(); // Empty classpath

//Start build from cache
IncrementalLauncher launcher = new IncrementalLauncher(inputResources, sourceClasspath, cache);

if (launcher.changesPresent()) {
    System.out.println("There are changes since last save to cache.");

CtModel newModel = launcher.buildModel();
//Model is now up to date

//Cache is now up to date