[groovy] compile time meta programming (compile time method interception | method interception in myasttransformation visit method)

One 、 stay MyASTTransformation#visit Method interception in method

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In the last blog 【Groovy】 Compile time metaprogramming ( Compile time method interception | stay MyASTTransformation#visit Method to intercept ) in , stay MyASTTransformation#visit In the method , First of all, I got ModuleNode , Then find the specified ClassNode , From the specified ClassNode Find the corresponding MethodNode node ;

Method interception is mainly in MethodNode Node ; The MethodNode The node corresponding to the Student Class hello Method ;

according to 【Groovy】 Compile time metaprogramming ( Method used in interception AST Syntax tree node MethodNode node | MethodNode Node analysis | MethodNode Nodes in the BlockStatement) Blog analysis , MethodNode The node encapsulates private Statement code; member , The code The actual type of member is BlockStatement type ;

public class BlockStatement extends Statement

First of all, I will MethodNode Node code Members are assigned to BlockStatement , Is equivalent to Statement Object to BlockStatement type ;

BlockStatement blockStatement = code

stay BlockStatement In the object , Encapsulates the private List<Statement> statements = new ArrayList<Statement>(); member , This is the MethodNode Method content in the node , Empty the collection , It is equivalent to emptying the method body , The method interception operation is implemented ;

Two 、 Complete code examples and the compilation process of compile time processing

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1、Groovy Script Groovy.groovy

class Student{ 
        def name    def hello(){ 
            println "hello"    }}def student = new Student()student.hello()

2、ASTTransformation Interface implementation MyASTTransformation.groovy

import org.codehaus.groovy.ast.ASTNodeimport org.codehaus.groovy.ast.builder.AstBuilderimport org.codehaus.groovy.ast.stmt.BlockStatementimport org.codehaus.groovy.control.SourceUnitimport org.codehaus.groovy.transform.ASTTransformationimport org.codehaus.groovy.transform.GroovyASTTransformation@GroovyASTTransformationclass MyASTTransformation implements ASTTransformation { 
        /** *  Compile time processing  * @param nodes AST  Abstract syntax tree node  ,  yes  ASTNode  An array type  * @param source  Source unit  ,  You can get the source file through this object  */    @Override    void visit(ASTNode[] nodes, SourceUnit source) { 
            println nodes        println source        println source.AST        println source.source.reader.text        //  obtain  Groovy.groovy  A collection of classes in a script  ,  And traverse         //  stay  ModuleNode  The class nodes in are encapsulated in the following members         // List<ClassNode> classes = new LinkedList<ClassNode>();        source.AST.classes.find { 
                //  The search name is  Student  Class             // it  yes  ClassNode  node             it.name == "Student"        }?.methods?.find { 
                //  lookup  Student  The name under the class is  hello  Methods             // it  yes  MethodNode  node             it.name == "hello"        }?.with { 
                //  eureka  Student  Under the  hello  Method             //  stay  MethodNode  Call under the node             // it  Namely  MethodNode  node             BlockStatement blockStatement = code            //  Empty  BlockStatement  Medium  List<Statement> statements  member             //  Method intercepts emptying  ,  No longer execute the original method             //  Method injection does not empty  ,  Will execute the original method content             blockStatement.statements.clear()        }    }}

3、 To configure ASTTransformation

establish D:\002_Project\012_Groovy\Groovy_Demo\src\main\groovy\resources\META-INF\servicesorg.codehaus.groovy.transform.ASTTransformation Directory level and documents , Configure... In a file ASTTransformation The full class name of the implementation class :

MyASTTransformation

3、 Use the command line for compile time processing

First , Get into D:\002_Project\012_Groovy\Groovy_Demo\src\main\groovy Catalog ,

cd D:\002_Project\012_Groovy\Groovy_Demo\src\main\groovy

then , compile Compile time processing class MyASTTransformation.groovy , The compiled bytecode file MyASTTransformation.class Save to D:\002_Project\012_Groovy\Groovy_Demo\src\main\groovy\classes Under the table of contents ,

groovyc -d classes MyASTTransformation.groovy

And then , Package the above compiled bytecode file , Store in D:\002_Project\012_Groovy\Groovy_Demo\src\main\groovy\test.jar route ;

jar -cf test.jar -C classes . -C resources .

Last , rely on test.jar perform Groovy.groovy Script

groovy -classpath test.jar Groovy.groovy

The execution result is :

[org.codehaus.groovy.ast.ModuleNode@7d7758be][e-mail]@7d7758beclass Student{ 
        def name    def hello(){ 
            println "hello"    }}def student = new Student()student.hello()