[开发工具]ASM库入门示例

概述

读取一个类的信息可以使用反射，但是在效率上，ASM比反射更快。

一、导入依赖

<!-- https://mvnrepository.com/artifact/org.ow2.asm/asm -->
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm</artifactId>
            <version>9.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.ow2.asm/asm-util -->
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-util</artifactId>
            <version>9.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.ow2.asm/asm-commons -->
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-commons</artifactId>
            <version>9.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.ow2.asm/asm-tree -->
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-tree</artifactId>
            <version>9.2</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.ow2.asm/asm-analysis -->
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-analysis</artifactId>
            <version>9.2</version>
        </dependency>

二、要被ASM读取类信息的User.class

public class User<T> {
    private Integer a = 1;
    private Integer c;
    private String b = "123";
    private List<Integer> list;
    private User user;
    private T data;
}

三、读取类信息

public class ReaderClassField {
    public static void main(String[] args) throws IOException {
        ClassReader classReader = new ClassReader(User.class.getName());
        SimpleClassVisitor simpleClassVisitor = new SimpleClassVisitor(Opcodes.ASM5);
        ClassNode classNode = new ClassNode();
        classReader.accept(simpleClassVisitor,0);


    }
}
class SimpleClassVisitor extends ClassVisitor{

    public SimpleClassVisitor(int i) {
        super(i);
    }
    @Override
    public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) {
        System.out.println(Thread.currentThread().getStackTrace()[1].getMethodName()+", access:"+access+", name:"+name+", desc:"+desc+", signature:"+signature+", value:"+value);

        return super.visitField(access, name, desc, signature, value);
    }
}

打印结果

可以看到字段信息被读出来了。