爱码博阁

1、引入java字节码操作库

<dependency>
    <groupId>org.javassist</groupId>
    <artifactId>javassist</artifactId>
    <version>3.27.0-GA</version>
    <scope>compile</scope>
    <optional>true</optional>
</dependency>

2、示例demo

创建空类

package com.sourcecode.helloworld.dto;

public class ExcelDto {
}

对空类进行添加属性

package com.sourcecode.helloworld.dynamic;

import javassist.*;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.HashSet;
import java.util.Set;

@RestController
public class TestController {

    private static Set<String> existSet = new HashSet<>();
    private static boolean exist = false;
    private static Class clazz;

    @GetMapping("/test")
    public void test(String property){

        Object obj = addFields(property.split(","));
        System.out.println(obj);

    }

    private Object addFields(String ...fields){
        int addCount = 0;
        try {
            //默认的类搜索路径
            ClassPool pool = ClassPool.getDefault();
            //获取一个ctClass对象
            CtClass ctClass = pool.getCtClass("com.sourcecode.helloworld.dto.ExcelDto");
            if(exist){
                ctClass.defrost();
            }
            for (String field : fields) {
                if(existSet.contains(field)){
                    continue;
                }
                //添加属性
                ctClass.addField(CtField.make(String.format("private String %s;", field), ctClass));
                //添加set方法
                ctClass.addMethod(CtMethod.make(String.format("public void set%s(String %s){this.%s = %s;}", captureName(field), field, field, field), ctClass));
                //添加get方法
                ctClass.addMethod(CtMethod.make(String.format("public int get%s(){return this.%s;}", captureName(field), field), ctClass));
            }
            for (String field : fields) {
                if(!existSet.contains(field)){
                    existSet.add(field);
                    addCount++;
                }
            }
            if(!exist){
                clazz = ctClass.toClass();
                exist = true;
            } else {
                if(addCount>0){
                    Loader classLoader = new Loader(pool);
                    clazz = classLoader.loadClass("com.sourcecode.helloworld.dto.ExcelDto");
                }
            }
            return clazz.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 将字符串的首字母转大写
     * @param str 需要转换的字符串
     * @return
     */
    private static String captureName(String str) {
        // 进行字母的ascii编码前移，效率要高于截取字符串进行转换的操作
        char[] cs=str.toCharArray();
        cs[0]-=32;
        return String.valueOf(cs);
    }

}