Java 动态为类添加属性

梦里梦外; 2023-06-06 10:37 1阅读 0赞

**“衰兰送客咸阳道，天若有情天亦老”**

## 序 ##

有一个这样的功能：展示一个报表，表头是动态的，可以手动新增或删除，也就是说会修改表结构，新增或删除表字段。然而一般实体类都是对应表结构的，那么如何给实体增加属性呢？虽然我自己的解决方案是直接返回`List<map>`，然后让对应的列适配到map的key中。但是这里说说给实体类动态添加属性。

## 实现代码 ##

import com.google.common.collect.Maps;
    import net.sf.cglib.beans.BeanGenerator;
    import net.sf.cglib.beans.BeanMap;
    import org.apache.commons.beanutils.PropertyUtilsBean;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import java.beans.PropertyDescriptor;
    import java.lang.reflect.Method;
    import java.util.HashMap;
    import java.util.Map;
    
    /** *@author *@date 2019/10/9 *@description */
    public class ReflectUtil { 
    
        static Logger logger = LoggerFactory.getLogger(ReflectUtil.class);
    
        public static Object getTarget(Object dest, Map<String, Object> addProperties) { 
            // get property map
            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
            for (Map.Entry<String, Object> entry : addProperties.entrySet()) { 
                propertyMap.put(entry.getKey(), entry.getValue().getClass());
            }
    // addProperties.forEach((k, v) -> propertyMap.put(k, v.getClass()));
            // new dynamic bean
            DynamicBean dynamicBean = new DynamicBean(dest.getClass(), propertyMap);
            // add old value
            for (Map.Entry<String, Class> entry : propertyMap.entrySet()) { 
                try { 
                    // filter extra properties
                    if (!addProperties.containsKey(entry.getKey())) { 
                        dynamicBean.setValue(entry.getKey(), propertyUtilsBean.getNestedProperty(dest, entry.getKey()));
                    }
                } catch (Exception e) { 
                    logger.error(e.getMessage(), e);
                }
            }
            ;
            // add extra value
            for (Map.Entry<String, Object> entry : addProperties.entrySet()) { 
                try { 
                    dynamicBean.setValue(entry.getKey(), entry.getValue());
                } catch (Exception e) { 
                    logger.error(e.getMessage(), e);
                }
            }
            ;
            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();
            }
        }
    
        public static void main(String[] args) { 
            TestClass entity = new TestClass();
            entity.setAge(15);
            entity.setId(1);
            entity.setName("张三");
            //动态设置属性字段
            Map<String, Object> addProperties = new HashMap() { { 
                put("sex", "男");
                put("telephone", "123456789");
            }};
            //获取实体中给属性的值
            Object target = getTarget(entity, addProperties);
            System.out.println(getFieldValueByName("id", target));
            System.out.println(getFieldValueByName("name", target));
            System.out.println(getFieldValueByName("age", target));
            System.out.println(getFieldValueByName("sex", target));
            System.out.println(getFieldValueByName("telephone", target));
        }
    
        //获取实体中属性的值
        private static Object getFieldValueByName(String fieldName, Object o) { 
            try { 
                //通过反射获取值
                String firstLetter = fieldName.substring(0, 1).toUpperCase();
                String getter = "get" + firstLetter + fieldName.substring(1);
                Method method = o.getClass().getMethod(getter, new Class[]{ });
                Object value = method.invoke(o, new Object[]{ });
                return value;
            } catch (Exception e) { 
                logger.error(e.getMessage(), e);
                return null;
            }
        }
    
        //测试类
        public static class TestClass{ 
            //ID
            private int id;
            //名字
            private String name;
            //年龄
            private int age;
    
            public int getId() { 
                return id;
            }
    
            public void setId(int id) { 
                this.id = id;
            }
    
            public String getName() { 
                return name;
            }
    
            public void setName(String name) { 
                this.name = name;
            }
    
            public int getAge() { 
                return age;
            }
    
            public void setAge(int age) { 
                this.age = age;
            }
        }
    
    }

结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfUnVubmVy_size_16_color_FFFFFF_t_70]  
本文参考至：[JAVA“动态”为类添加属性][JAVA]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0FfUnVubmVy_size_16_color_FFFFFF_t_70]: /images/20230601/3f9d301b507349128ae57fcf332c89b8.png
[JAVA]: https://www.cnblogs.com/frinder6/p/7204574.html