java注解和反射示例

最近做项目中有接触到反射的使用简单的做了一个注释

首先的想法是根据类中不为空的值生成sql

 

首先是三个注解

主键注解

package comments;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 主键
 * @author  Administrator
 */
@Target(ElementType.FIELD)   
@Retention(RetentionPolicy.RUNTIME)   
@Documented  
@Inherited 
public @interface  Key {
}
package comments;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 如果不和数据关联则设置此注解
 * @author  Administrator
 *
 */
@Target(ElementType.FIELD)   
@Retention(RetentionPolicy.RUNTIME)   
@Documented  
@Inherited 
public @interface  notRecord {
}
package comments;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 设置表名
 * @author  Administrator
 *
 */
@Target(ElementType.TYPE)   
@Retention(RetentionPolicy.RUNTIME)   
@Documented  
@Inherited 
public @interface  Table {
	public String name();
}
然后是自定义异常类
package org;

/**
 * 设置自定义异常
 * @author  Administrator
 *
 */
public class NumException extends Exception {
	private String name;
	public NumException(String name){
		this.name=name;
	}
	public String toString(){
		  return name;
	}
}
实体类
package org;

import comments.Key;
import comments.Table;
import comments.notRecord;

@Table(name = "student")
public class Student {
	@Key 
	private String id;
	private String name;
	@notRecord
	private String sex;
	private int age;

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}
}
处理实体类生成sql的类。
package org;

import java.lang.reflect.Field;

import comments.Key;
import comments.Table;
import comments.notRecord;

public class Processing {
	
	/**
	 * 通过实体类生成 insert into sql语句
	 * @param cl
	 * @return 
	 * @throws IllegalArgumentException
	 * @throws IllegalAccessException
	 * @throws NumException
	 */
	public String save(Object cl) throws IllegalArgumentException, IllegalAccessException, NumException{
		String sql="insert into ";
		if(cl!=null){
			Field[] fiels=cl.getClass().getDeclaredFields();//获得反射对象集合
			boolean t=cl.getClass().isAnnotationPresent(Table.class);//获得类是否有注解
			if(t){
				Table tab=cl.getClass().getAnnotation(Table.class);
				sql+=tab.name();//获得表名
				String name ="";//记录字段名
				String value ="";//记录值名称
				boolean bl=false;//记录主键是否为空
				for(Field fl:fiels){//循环组装
					fl.setAccessible(true);//开启支私有变量的访问权限
					Object tobj=fl.get(cl);
					if(tobj!=null){
						if(fl.isAnnotationPresent(Key.class)){//判断是否存在主键
							bl=true;
						}
						if(!fl.isAnnotationPresent(notRecord.class)){
							name+=fl.getName()+",";
							value+="'"+tobj.toString()+"',";
						}
					}
				}
				if(bl){
					if(name.length()>0)
						name=name.substring(0,name.length()-1);
					if(value.length()>0)
						value=value.substring(0,value.length()-1);
					sql+="("+name+") values("+value+")";
				}else
					throw new NumException("未找到类主键 主键不能为空");
			}else
				throw new NumException("传入对象不是实体类");
		}else
			 throw new NumException("传入对象不能为空");//抛出异常
		return sql;
	}
	/**
	 * 传入对象更新
	 * @param obj
	 * @return 
	 * @throws IllegalArgumentException
	 * @throws IllegalAccessException
	 * @throws NumException
	 */
	public String update(Object obj) throws IllegalArgumentException, IllegalAccessException, NumException{
		String sql="update ";
		if(obj!=null){
			Field[] fiels=obj.getClass().getDeclaredFields();//获得反射对象集合
			boolean t=obj.getClass().isAnnotationPresent(Table.class);//获得类是否有注解
			if(t){
				Table tab=obj.getClass().getAnnotation(Table.class);
				sql+=tab.name()+" set ";//获得表名
				String wh ="";//记录字段名
				String k="";
				boolean bl=false;//记录主键是否为空
				for(Field fl:fiels){//循环组装
					fl.setAccessible(true);//开启支私有变量的访问权限
					Object tobj=fl.get(obj);
					if(tobj!=null){
						if(fl.isAnnotationPresent(Key.class)){//判断是否存在主键
							bl=true;
							k=fl.getName()+"='"+tobj.toString()+"' where  ";
						}else{
							if(!fl.isAnnotationPresent(notRecord.class)){
								wh+=fl.getName()+"='"+tobj.toString()+"',";
							}
						}
					}
				}
				if(bl){
					if(wh.length()>0)
						wh=wh.substring(0,wh.length()-1);
					if(k.length()>0)
						k=k.substring(0,k.length()-1);
					sql+=k+wh;
				}else
					throw new NumException("未找到类主键 主键不能为空");
			}else
				throw new NumException("传入对象不是实体类");
		}else
			 throw new NumException("传入对象不能为空");//抛出异常
		return sql;
	}
}
 

最后是测试类

package org;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import comments.Table;
import comments.Key;

public class temp {
	public static void main(String[] aa) throws IllegalArgumentException, IllegalAccessException, NumException{
		Student stu=new Student();
		stu.setId("ccc");
		stu.setName("姓名");
		stu.setAge(18);
		stu.setSex("男");
		//stu=null;
		System.out.println(new Processing().save(stu));
		System.out.println(new Processing().update(stu));
	}
}