创建ASTParser并将Java源文件解析成AST:
- // Initialize ASTParser
- ASTParser parser = ASTParser.newParser(AST.JLS3); //initialize
- parser.setKind(ASTParser.K_COMPILATION_UNIT); //to parse compilation unit
- parser.setSource(content.toCharArray()); //content is a string which stores the java source
- parser.setResolveBindings(true);
- CompilationUnit result = (CompilationUnit) parser.createAST(null);
调用imports()方法得到源文件的一系列import声明:
- //show import declarations in order
- List importList = result.imports();
- System.out.println("import:");
- for(Object obj : importList) {
- ImportDeclaration importDec = (ImportDeclaration)obj;
- System.out.println(importDec.getName());
- }
调用types()方法得到类名称:
- //show class name
- List types = result.types();
- TypeDeclaration typeDec = (TypeDeclaration) types.get(0);
- System.out.println("className:"+typeDec.getName());
调用TypeDeclaration的getField方法得到类里定义的field:
- //show fields
- FieldDeclaration fieldDec[]=typeDec.getFields();
- System.out.println("Fields:");
- for(FieldDeclaration field: fieldDec)
- {
- System.out.println("Field fragment:"+field.fragments());
- System.out.println("Field type:"+field.getType());
- }
调用TypeDeclaration的getMethods方法得到类里定义的list of methods;同理,可以调用MethodDeclaration里的各种方法得到method的方法名,参数,返回类型等等:
- //show methods
- MethodDeclaration methodDec[] = typeDec.getMethods();
- System.out.println("Method:");
- for (MethodDeclaration method : methodDec)
- {
- //get method name
- SimpleName methodName=method.getName();
- System.out.println("method name:"+methodName);
- //get method parameters
- List param=method.parameters();
- System.out.println("method parameters:"+param);
- //get method return type
- Type returnType=method.getReturnType2();
- System.out.println("method return type:"+returnType);
一个方法的内容对应一个block,可以用getBody()得到;一个block又可以被分解成一系列statements,可以用statements()方法得到:
- //get method body
- Block body=method.getBody();
- List statements=body.statements(); //get the statements of the method body
- Iterator iter=statements.iterator();
- while(iter.hasNext())
- {
- //get each statement
- Statement stmt=(Statement)iter.next();
接下来需要根据每个statement的类型来对源码进行相应的解析。Statement有很多子类,这里只给出其中的几类介绍(具体可以参考我上一篇文章:ASTParser介绍;最好直接去Eclipse documentation官网查看相关文档)。基本流程就是先判断statement是哪种类型的实例,做出相应的ClassCast,再调用相应的方法。
1. ExpressionStatement (又包括Assignement, MethodInvocation等子类)。
- if(stmt instanceof ExpressionStatement)
- {
- ExpressionStatement expressStmt=(ExpressionStatement) stmt;
- Expression express=expressStmt.getExpression();
- if(express instanceof Assignment)
- {
- Assignment assign=(Assignment)express;
- System.out.println("LHS:"+assign.getLeftHandSide()+"; ");
- System.out.println("Op:"+assign.getOperator()+"; ");
- System.out.println("RHS:"+assign.getRightHandSide());
- }
- else if(express instanceof MethodInvocation)
- {
- MethodInvocation mi=(MethodInvocation) express;
- System.out.println("invocation name:"+mi.getName());
- System.out.println("invocation exp:"+mi.getExpression());
- System.out.println("invocation arg:"+mi.arguments());
- }
- System.out.println();
- }
2. IfStatement
- else if(stmt instanceof IfStatement)
- {
- IfStatement ifstmt=(IfStatement) stmt;
- InfixExpression wex=(InfixExpression) ifstmt.getExpression();
- System.out.println("if-LHS:"+wex.getLeftOperand()+"; ");
- System.out.println("if-op:"+wex.getOperator()+"; ");
- System.out.println("if-RHS:"+wex.getRightOperand());
- System.out.println();
- }
3. VariableDeclarationStatement
- else if(stmt instanceof VariableDeclarationStatement)
- {
- VariableDeclarationStatement var=(VariableDeclarationStatement) stmt;
- System.out.println("Type of variable:"+var.getType());
- System.out.println("Name of variable:"+var.fragments());
- System.out.println();
- }
4. ReturnStatement
- else if(stmt instanceof ReturnStatement)
- {
- ReturnStatement rtstmt=(ReturnStatement) stmt;
- System.out.println("return:"+rtstmt.getExpression());
- System.out.println();
- }
ASTParser 作为programming language编译器的一部分,功能机制可以说是相当强大。以上的例子只是冰山一角。使用ASTParser可以对java的源文件进行各种解析,用户只需要指明源文件,调用一下ASTParser的createAST方法就能得到完整的AST了,剩下的就是用户根据实际需要对AST进行各种manipulate了。