使用JavaParser进行java源码解析

JavaParser下载地址：http://code.google.com/p/javaparser/downloads/list

刚开始接触的时候觉得和JDT里的Parser类不太一样。查了一下WiKi，发现它访问编译单元成员，需要调用相应子元素对应的Visitor类的visit（）方法。此方法可以通过复写来实现自己需要的功能。我需要的功能是将编译单元里的所有MethodDeclaration取出，因此利用传递句柄的方式，实现代码如下：

public static List<MethodDeclaration> getMethodList(CompilationUnit cu) {
List<MethodDeclaration> methodList = new ArrayList<MethodDeclaration>();
new MethodGetterVisitor().visit(cu, methodList);

return methodList;
}

private static class MethodGetterVisitor extends VoidVisitorAdapter<Object> {

@SuppressWarnings("unchecked")
@Override
public void visit(MethodDeclaration n, Object arg) {
List<MethodDeclaration> methodList = new ArrayList<MethodDeclaration>();
methodList =  (List<MethodDeclaration>) arg;
methodList.add(n);
}
}

官方还提供了不通过Visitor改变一个类成员方法的示例（相对Visitor更复杂）：

public class MethodChanger {

public static void main(String[] args) throws Exception {
// creates an input stream for the file to be parsed
FileInputStream in = new FileInputStream("test.java");

CompilationUnit cu;
try {
// parse the file
cu = JavaParser.parse(in);
} finally {
in.close();
}

// change the methods names and parameters
changeMethods(cu);

// prints the changed compilation unit
System.out.println(cu.toString());
}

private static void changeMethods(CompilationUnit cu) {
List<TypeDeclaration> types = cu.getTypes();
for (TypeDeclaration type : types) {
List<BodyDeclaration> members = type.getMembers();
for (BodyDeclaration member : members) {
if (member instanceof MethodDeclaration) {
MethodDeclaration method = (MethodDeclaration) member;
changeMethod(method);
}
}
}
}

private static void changeMethod(MethodDeclaration n) {
// change the name of the method to upper case
n.setName(n.getName().toUpperCase());

// create the new parameter
Parameter newArg = ASTHelper.createParameter(ASTHelper.INT_TYPE, "value");

// add the parameter to the method
ASTHelper.addParameter(n, newArg);
}
}

最后附上WiKi里给出的编译单元创建示例：

public class ClassCreator {

public static void main(String[] args) throws Exception {
// creates the compilation unit
CompilationUnit cu = createCU();

// prints the created compilation unit
System.out.println(cu.toString());
}

/**
* creates the compilation unit
*/
private static CompilationUnit createCU() {
CompilationUnit cu = new CompilationUnit();
// set the package
cu.setPakage(new PackageDeclaration(ASTHelper.createNameExpr("java.parser.test")));

// create the type declaration
ClassOrInterfaceDeclaration type = new ClassOrInterfaceDeclaration(ModifierSet.PUBLIC, false, "GeneratedClass");
ASTHelper.addTypeDeclaration(cu, type);

// create a method
MethodDeclaration method = new MethodDeclaration(ModifierSet.PUBLIC, ASTHelper.VOID_TYPE, "main");
method.setModifiers(ModifierSet.addModifier(method.getModifiers(), ModifierSet.STATIC));
ASTHelper.addMember(type, method);

// add a parameter to the method
Parameter param = ASTHelper.createParameter(ASTHelper.createReferenceType("String", 0), "args");
param.setVarArgs(true);
ASTHelper.addParameter(method, param);

// add a body to the method
BlockStmt block = new BlockStmt();
method.setBody(block);

// add a statement do the method body
NameExpr clazz = new NameExpr("System");
FieldAccessExpr field = new FieldAccessExpr(clazz, "out");
MethodCallExpr call = new MethodCallExpr(field, "println");
ASTHelper.addArgument(call, new StringLiteralExpr("Hello World!"));
ASTHelper.addStmt(block, call);

return cu;
}
}