java为实体动态添加字段

    对于线上已经在用的接口，要动态的扩展返回数据的字段，并且不同的调用商需要的字段不一样，为了A客户增加了一个字段，不能把字段返回给B，防止B客户那边也要升级接口。对于开始加一两个字段我还可以接受：每次返回不同的实例，渐渐的我觉得力不从心了，代码重复太多了，就想到了能不能动态的添加字段呢？
首先引入maven依赖：

        <dependency>
            <groupId>commons-beanutils</groupId>
            <artifactId>commons-beanutils</artifactId>
            <version>1.9.3</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.8</version>
        </dependency>
        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib-nodep</artifactId>
            <version>3.2.4</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.22</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.6</version>
        </dependency>

代码中使用：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.collect.Maps;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import net.sf.cglib.beans.BeanGenerator;
import net.sf.cglib.beans.BeanMap;
import org.apache.commons.beanutils.PropertyUtilsBean;

import java.beans.PropertyDescriptor;
import java.util.Map;

/**
 * @author: jack
 * @Date: 2019/5/15 21:30
 * @Description: 动态添加类的属性
 */
public class ReflectUtil {
    public static Object getTarget(Object dest, Map<String, Object> addProperties) {
        PropertyUtilsBean propertyUtilsBean =new PropertyUtilsBean();
        PropertyDescriptor[] descriptors = propertyUtilsBean.getPropertyDescriptors(dest);
        Map<String, Class> propertyMap = Maps.newHashMap();
        for(PropertyDescriptor d : descriptors) {
            if(!"class".equalsIgnoreCase(d.getName())) {
                propertyMap.put(d.getName(), d.getPropertyType());
            }
        }
        // add extra properties
        addProperties.forEach((k, v) -> propertyMap.put(k, v.getClass()));
        // new dynamic bean
        DynamicBean dynamicBean =new DynamicBean(dest.getClass(), propertyMap);
        // add old value
        propertyMap.forEach((k, v) -> {
            try{
                // filter extra properties
                if(!addProperties.containsKey(k)) {
                    dynamicBean.setValue(k, propertyUtilsBean.getNestedProperty(dest, k));
                }
            }catch (Exception e) {
                e.printStackTrace();
            }
        });
        // add extra value
        addProperties.forEach((k, v) -> {
            try{
                dynamicBean.setValue(k, v);
            }catch (Exception e) {
                e.printStackTrace();
            }
        });
        Object target = dynamicBean.getTarget();
        return target;
    }

    public static class DynamicBean {
        /**
         * 目标对象
         */
        private Object target;

        /**
         * 属性集合
         */
        private BeanMap beanMap;

        public DynamicBean(Class superclass, Map<String, Class> propertyMap) {
            this.target = generateBean(superclass, propertyMap);
            this.beanMap = BeanMap.create(this.target);
        }


        /**
         * bean 添加属性和值
         *
         * @param property
         * @param value
         */
        public void setValue(String property, Object value) {
            beanMap.put(property, value);
        }

        /**
         * 获取属性值
         *
         * @param property
         * @return
         */
        public Object getValue(String property) {
            return beanMap.get(property);
        }

        /**
         * 获取对象
         *
         * @return
         */
        public Object getTarget() {
            return this.target;
        }


        /**
         * 根据属性生成对象
         *
         * @param superclass
         * @param propertyMap
         * @return
         */
        private Object generateBean(Class superclass, Map<String, Class> propertyMap) {
            BeanGenerator generator =new BeanGenerator();
            if(null != superclass) {
                generator.setSuperclass(superclass);
            }
            BeanGenerator.addProperties(generator, propertyMap);
            return generator.create();
        }
    }

    @Data
    @Builder
    @AllArgsConstructor
    @NoArgsConstructor
    public static class Student {
        private String name;
        private String email;
    }


    public static void main(String[] args) throws Exception{
        Student student = Student.builder().name("jack").email("xy123zk@163.com").build();
        System.out.println(student.toString());
        Map<String,Object> properties = Maps.newHashMap();
        properties.put("address","浙江杭州");
        properties.put("age",26);
        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writeValueAsString(getTarget(student,properties));
        System.out.println(json);
    }
}

结果：

image.png
在spring集成的web项目可以直接使用spring提供的类，可以把依赖的net.sf.cglib.beans.BeanGenerator和net.sf.cglib.beans.BeanMap直接换成org.springframework.cglib.beans.BeanGenerator和org.springframework.cglib.beans.BeanMap

参考：
1.http://www.cnblogs.com/frinder6/p/7204574.html