II: ByteBuddy入门笔记2

OnMethodEnter Advice

先编写一个入门示例 项目源码结构如下

pom.xml

<project>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>net.bytebuddy</groupId>
                <artifactId>byte-buddy-maven-plugin</artifactId>
                <version>1.14.5</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>transform</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <transformations>
                        <transformation>
                            <plugin>com.importzhh.InterceptorPlugin</plugin>
                        </transformation>
                    </transformations>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

DataProducer.java

package com.importzhh;

public class DataProducer {
    public DataProducer() {
    }

    public void create() {
        System.out.println("Method start");
        System.out.println("create data");
    }
}

LogInterceptor.java

package com.importzhh;

import net.bytebuddy.asm.Advice;

public class LogInterceptor {
    @Advice.OnMethodEnter
    public static void start() {
        System.out.println("Method start");
    }
}

package com.importzhh;

import net.bytebuddy.asm.Advice;
import net.bytebuddy.build.Plugin;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.dynamic.ClassFileLocator;
import net.bytebuddy.dynamic.DynamicType;
import net.bytebuddy.matcher.ElementMatchers;

import java.io.IOException;

public class InterceptorPlugin implements Plugin {
    @Override
    public DynamicType.Builder<?> apply(DynamicType.Builder<?> builder, TypeDescription typeDescription, ClassFileLocator classFileLocator) {
        return builder.visit(Advice.
                to(LogInterceptor.class).
                on(ElementMatchers.named("create")));
    }

    @Override
    public void close() throws IOException {
        System.out.println("InterceptorPlugin close method");
    }

    @Override
    public boolean matches(TypeDescription target) {
        System.out.println("Inspecting" + target.getName());
        if (target.getName().equals(DataProducer.class.getName())) {
            System.out.println("Found target code : " + target.getName());
            return true;
        } else {
            System.out.println("Inspected code" + target.getName() + "is not the target code");
            return false;
        }

    }
}

App.java

package com.importzhh;

/**
 * Hello world!
 */
public class App {
    public static void main(String[] args) {
        System.out.println("Hello World!");
        new DataProducer().create();
    }
}

在InterceptorPlugin中定义了字节码转换规则（即为 DataProducer.create 方法添加日志），接下来的步骤是编译并测试这个插件。

1. 编译：你可以使用Maven进行编译，确保整个项目没有语法错误和依赖问题。在项目的根目录运行以下命令进行编译：

mvn clean install

2. 运行：InterceptorPlugin 定义了对 DataProducer.create 方法的转换逻辑。

在编译阶段，ByteBuddy Maven插件应该会修改 DataProducer 类的字节码，并为 create 方法添加 “Method start” 的输出。因此，调用 DataProducer.create 应该能看到这个输出。

运行这个 App.java 测试，如果一切正常，那么在控制台中应该看到 “Method start” 的输出。

Hello World!
Method start
create data