JavaBean动态添加删除属性

1.cglib

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

输出结果:
name1
getId
getUsername
setId
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

DynaProperty property = new DynaProperty("id", Long.class);
DynaProperty property1 = new DynaProperty("username", String.class);
BasicDynaClass basicDynaClass = new BasicDynaClass("user", null, new DynaProperty[]{property, property1});
BasicDynaBean basicDynaBean = new BasicDynaBean(basicDynaClass);
User user = new User();
user.setId(1L);
user.setUsername("name1");
user.setPassword("123");

BeanUtils.copyProperties(basicDynaBean, user);
Map<String, Object> map = basicDynaBean.getMap();
Iterator<String> it = map.keySet().iterator();
while (it.hasNext()) {
    String key = it.next();
    System.out.println(key + ":" + map.get(key));
}

输入结果:
id:1
username:name1

查看BasicDynaBean与BasicDynaClass之间的关系

DynaBean的源码

public interface DynaBean {

    public boolean contains(String name, String key);

    public Object get(String name);

    public Object get(String name, int index);

    public Object get(String name, String key);

    public DynaClass getDynaClass();

    public void remove(String name, String key);

    public void set(String name, Object value);

    public void set(String name, int index, Object value);

    public void set(String name, String key, Object value);


}

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);

/**
 * Return the value of a simple property with the specified name.
 *
 * @param name Name of the property whose value is to be retrieved
 * @return The property's value
 *
 * @exception IllegalArgumentException if there is no property
 *  of the specified name
 */
public Object get(String name) {

    // Return any non-null value for the specified property
    Object value = values.get(name);
    if (value != null) {
        return (value);
    }

    // Return a null value for a non-primitive property
    Class<?> type = getDynaProperty(name).getType();
    if (!type.isPrimitive()) {
        return (value);
    }

    // Manufacture default values for primitive properties
    if (type == Boolean.TYPE) {
        return (Boolean.FALSE);
    } else if (type == Byte.TYPE) {
        return (new Byte((byte) 0));
    } else if (type == Character.TYPE) {
        return (new Character((char) 0));
    } else if (type == Double.TYPE) {
        return (new Double(0.0));
    } else if (type == Float.TYPE) {
        return (new Float((float) 0.0));
    } else if (type == Integer.TYPE) {
        return (new Integer(0));
    } else if (type == Long.TYPE) {
        return (new Long(0));
    } else if (type == Short.TYPE) {
        return (new Short((short) 0));
    } else {
        return (null);
    }

}

从以上代码可以看出是在values里取值的

    /**
     * The set of property values for this DynaBean, keyed by property name.
     */
    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.

关于复制属性可以参看:

java复制属性