使用mixin来记录bean属性的改变

先定义一个需要被introduce的interface

java 代码

public interface EditAware {

    public Object getOldValue(String propertyName);

    public boolean isEdited(String propertyName);

}

再写这个interface的mixin

java 代码

import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.beanutils.PropertyUtils;
import org.apache.commons.lang.StringUtils;
import org.springframework.aop.support.DelegatingIntroductionInterceptor;

public class EditAwareMixin extends DelegatingIntroductionInterceptor implements
        EditAware {

    private transient Map map = new HashMap();

    public Object getOldValue(String propertyName) {
        return map.get(propertyName);
    }

    public boolean isEdited(String propertyName) {
        return map.containsKey(propertyName);
    }

    public Object invoke(MethodInvocation invocation) throws Throwable {
        if (invocation.getMethod().getName().indexOf("set") == 0) {
            Object _this = invocation.getThis();
            String propertyName = invocation.getMethod().getName().substring(3);
            propertyName = StringUtils.uncapitalize(propertyName);
            Object oldValue = PropertyUtils.getProperty(_this, propertyName);
            Object newValue = invocation.getArguments()[0];
            if (!isEquals(oldValue, newValue))
                map.put(propertyName, oldValue);
        }
        return super.invoke(invocation);
    }

    public static boolean isEquals(Object oldValue, Object newValue) {
        if (oldValue == null && newValue == null)
            return true;
        if (oldValue != null)
            return oldValue.equals(newValue);
        else
            return newValue.equals(oldValue);
    }
}

最后是怎么使用这个mixin

java 代码

import org.springframework.aop.framework.ProxyFactory;
import org.springframework.beans.BeanUtils;

public class Main {

    public static void main(String[] args) {
        User u1 = new User("username1", "password1");
        User u2 = new User("username2", "password2");
        ProxyFactory pc = new ProxyFactory();
        pc.setProxyTargetClass(true);
        pc.setTargetClass(u1.getClass());
        pc.addAdvice(new EditAwareMixin());
        pc.setTarget(u1);
        u1 = (User) pc.getProxy();
        BeanUtils.copyProperties(u2, u1);
        EditAware ea = (EditAware) u1;
        System.out.println(ea.isEdited("username"));
        System.out.println(ea.getOldValue("username"));
    }

    public static class User {
        private String username;
        private String password;

        public User() {

        }

        public User(String username, String password) {
            this.username = username;
            this.password = password;
        }

        public String getUsername() {
            return username;
        }

        public void setUsername(String username) {
            this.username = username;
        }

        public String getPassword() {
            return password;
        }

        public void setPassword(String password) {
            this.password = password;
        }

    }
}