Java cglib为实体类(javabean)动态添加属性方式

1.应用场景

之前对接三方平台遇到一个参数名称是变化的，然后我就想到了动态javabean怎么生成，其实是我想多了，用个map就轻易解决了，但还是记录下动态属性添加的实现吧。

2.引入依赖

1. <!--使用cglib 为javabean动态添加属性-->
2. <dependency>
3. <groupId>commons-beanutils</groupId>
4. <artifactId>commons-beanutils</artifactId>
5. <version>1.9.3</version>
6. </dependency>
7. <dependency>
8. <groupId>cglib</groupId>
9. <artifactId>cglib-nodep</artifactId>
10. <version>3.2.4</version>
11. </dependency>

3.代码如下

1. import com.freemud.waimai.menu.dpzhcto.dto.DynamicBean;
2. import com.google.common.collect.Maps;
3. import org.apache.commons.beanutils.PropertyUtilsBean;
4. import java.beans.PropertyDescriptor;
5. import java.util.Map;
6. public class PicBeanAddPropertiesUtil {
7. public static Object getTarget(Object dest, Map<String, Object> addProperties) {
8. // get property map
9. PropertyUtilsBean propertyUtilsBean = new PropertyUtilsBean();
10. PropertyDescriptor[] descriptors = propertyUtilsBean.getPropertyDescriptors(dest);
11. Map<String, Class> propertyMap = Maps.newHashMap();
12. for (PropertyDescriptor d : descriptors) {
13. if (!"class".equalsIgnoreCase(d.getName())) {
14. propertyMap.put(d.getName(), d.getPropertyType());
15. }
16. }
17. // add extra properties
18. addProperties.forEach((k, v) -> propertyMap.put(k, v.getClass()));
19. // new dynamic bean
20. DynamicBean dynamicBean = new DynamicBean(dest.getClass(), propertyMap);
21. // add old value
22. propertyMap.forEach((k, v) -> {
23. try {
24. // filter extra properties
25. if (!addProperties.containsKey(k)) {
26. dynamicBean.setValue(k, propertyUtilsBean.getNestedProperty(dest, k));
27. }
28. } catch (Exception e) {
29. e.printStackTrace();
30. }
31. });
32. // add extra value
33. addProperties.forEach((k, v) -> {
34. try {
35. dynamicBean.setValue(k, v);
36. } catch (Exception e) {
37. e.printStackTrace();
38. }
39. });
40. Object target = dynamicBean.getTarget();
41. return target;
42. }
43. }

1. import net.sf.cglib.beans.BeanGenerator;
2. import net.sf.cglib.beans.BeanMap;
3. import java.util.Map;
4. public class DynamicBean {
5. /**
6. * 目标对象
7. */
8. private Object target;
9. /**
10. * 属性集合
11. */
12. private BeanMap beanMap;
13. public DynamicBean(Class superclass, Map<String, Class> propertyMap) {
14. this.target = generateBean(superclass, propertyMap);
15. this.beanMap = BeanMap.create(this.target);
16. }
17. /**
18. * bean 添加属性和值
19. *
20. * @param property
21. * @param value
22. */
23. public void setValue(String property, Object value) {
24. beanMap.put(property, value);
25. }
26. /**
27. * 获取属性值
28. *
29. * @param property
30. * @return
31. */
32. public Object getValue(String property) {
33. return beanMap.get(property);
34. }
35. /**
36. * 获取对象
37. *
38. * @return
39. */
40. public Object getTarget() {
41. return this.target;
42. }
43. /**
44. * 根据属性生成对象
45. *
46. * @param superclass
47. * @param propertyMap
48. * @return
49. */
50. private Object generateBean(Class superclass, Map<String, Class> propertyMap) {
51. BeanGenerator generator = new BeanGenerator();
52. if (null != superclass) {
53. generator.setSuperclass(superclass);
54. }
55. BeanGenerator.addProperties(generator, propertyMap);
56. return generator.create();
57. }
58. }
59. public static void main(String[] args) {
60. FinalPicBaseReqDto entity = new FinalPicBaseReqDto();
61. entity.setAppKey("eee");
62. entity.setContent("222");
63. Map<String, Object> addProperties = new HashMap() {{
64. put("动态属性名", "动态属性值");
65. }};
66. FinalPicBaseReqDto finalPicBaseReqVo = (FinalPicBaseReqDto) PicBeanAddPropertiesUtil.getTarget(entity, addProperties);
67. System.out.println(JSON.toJSONString(finalPicBaseReqVo));
68. }

可以看到实体类只有两个属性，但是最终是动态添加进去了新的属性。

声明：代码也是前人造的*，欢迎各位拿去使用，解决实际生产中遇到的相似场景问题

补充：JavaBean动态添加删除属性

1.cglib

1. BeanGenerator beanGenerator = new BeanGenerator();
2. beanGenerator.addProperty("id", Long.class);
3. beanGenerator.addProperty("username", String.class);
4. Object obj = beanGenerator.create();
5. BeanMap beanMap = BeanMap.create(obj);
6. BeanCopier copier = BeanCopier.create(User.class, obj.getClass(), false);
7. User user = new User();
8. user.setId(1L);
9. user.setUsername("name1");
10. user.setPassword("123");
11. copier.copy(user, obj, null);
12. System.out.println(beanMap.get("username"));Class clazz = obj.getClass();
13. Method[] methods = clazz.getDeclaredMethods();for (int i = 0; i < methods.length; i++) {
14. System.out.println(methods[i].getName());
15. }

输出结果:

1. name1
2. getId
3. getUsername
4. setId
5. setUsername

从输出结果可以看出最后生成的obj只有id和username两个属性

2.org.apache.commons.beanutils

1. DynaProperty property = new DynaProperty("id", Long.class);
2. DynaProperty property1 = new DynaProperty("username", String.class);
3. BasicDynaClass basicDynaClass = new BasicDynaClass("user", null, newDynaProperty[]{property, property1});
4. BasicDynaBean basicDynaBean = new BasicDynaBean(basicDynaClass);
5. User user = new User();
6. user.setId(1L);
7. user.setUsername("name1");
8. user.setPassword("123");
9. BeanUtils.copyProperties(basicDynaBean, user);Map<String, Object> map = basicDynaBean.getMap();
10. Iterator<String> it = map.keySet().iterator();while (it.hasNext()) { String key = it.next();
11. System.out.println(key + ":" + map.get(key));
12. }

输入结果:

1. id:1username:name1

查看BasicDynaBean与BasicDynaClass之间的关系

DynaBean的源码

1. public interface DynaBean {
2. public boolean contains(String name, String key);
3. public Object get(String name);
4. public Object get(String name, int index);
5. public Object get(String name, String key);
6. public DynaClass getDynaClass();
7. public void remove(String name, String key);
8. public void set(String name, Object value);
9. public void set(String name, int index, Object value);
10. public void set(String name, String key, Object value);
11. }

主要是接口的定义

再来看看BasicDynaBean是怎么实现的,直接看public Object get(String name);

1. /**
2. * Return the value of a simple property with the specified name.
3. *
4. * @param name Name of the property whose value is to be retrieved
5. * @return The property's value
6. *
7. * @exception IllegalArgumentException if there is no property
8. * of the specified name
9. */public Object get(String name) { // Return any non-null value for the specified property
10. Object value = values.get(name); if (value != null) { return (value);
11. } // Return a null value for a non-primitive property
12. Class<?> type = getDynaProperty(name).getType(); if (!type.isPrimitive()) { return(value);
13. } // Manufacture default values for primitive properties
14. if (type == Boolean.TYPE) { return (Boolean.FALSE);
15. } else if (type == Byte.TYPE) { return (new Byte((byte) 0));
16. } else if (type == Character.TYPE) { return (new Character((char) 0));
17. } else if (type == Double.TYPE) { return (new Double(0.0));
18. } else if (type == Float.TYPE) { return (new Float((float) 0.0));
19. } else if (type == Integer.TYPE) { return (new Integer(0));
20. } else if (type == Long.TYPE) { return (new Long(0));
21. } else if (type == Short.TYPE) { return (new Short((short) 0));
22. } else { return (null);
23. }
24. }

从以上代码可以看出是在values里取值的

1. /**
2. * The set of property values for this DynaBean, keyed by property name.
3. */
4. protected HashMap<String, Object> values = new HashMap<String, Object>();

其实是用HashMap来实现的.

3.总结

用cglib动态删除添加属性时,虽然obj里有getUsername这个方法,却不能obj.getUsername()这样直接调用,想得到username的值只能通过beanMap.get("username")获取.

org.apache.commons.beanutils从源码来看是使用HashMap来实现的.

两种方式从操作角度来说和使用Map的区别不大.只是它们都提供了复制属性的工具方法.

原文链接：https://www.jianshu.com/p/cc1014e71e8a