import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;import a.jery.NotNull;public final class Demo {    public static void main(String[] args) {        Person p=new Person();p.setPersonName("123");CheckRS rs=check(p);System.out.println(String.format("flag:%s,msg:%s.", rs.getFlag(),rs.getMsg()));p.setPersonName(null);rs=check(p);System.out.println(String.format("flag:%s,msg:%s.", rs.getFlag(),rs.getMsg()));System.exit(0);}@SuppressWarnings({ "rawtypes"})public static CheckRS check(Object param){CheckRS rs=new CheckRS();Class cls=param.getClass();try {            BeanInfo beanInfo=Introspector.getBeanInfo(cls);PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();for(PropertyDescriptor pd:pds){Method readMethod=pd.getReadMethod();Method writeMethod=pd.getWriteMethod();if(null!=readMethod&&null!=writeMethod){Field field=cls.getDeclaredField(pd.getName());if(null!=field&&null!=field.getAnnotation(NotNull.class)){if(null==readMethod.invoke(param)){rs.setFlag(false);rs.setMsg(field.getAnnotation(NotNull.class).value());break;}                        }}}} catch (Exception e) {e.printStackTrace();}return rs;}}

flag:true,msg:null.
flag:false,msg:姓名不可为空.

package a.jery;import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;@Target({java.lang.annotation.ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface NotNull {String value() default "NotNull.value";
}

import a.jery.NotNull;public class Person {    @NotNull("姓名不可为空")private String personName;public String getPersonName() {return personName;}public void setPersonName(String personName) {this.personName = personName;}    }