java注解和反射制作dao基类的练习

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;@notRecordprivate 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+")";}elsethrow new NumException("未找到类主键 主键不能为空");}elsethrow 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;}elsethrow new NumException("未找到类主键 主键不能为空");}elsethrow 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));}}

这里如果要套用着DAO用就好了。我只是简单的实现一下。欢迎拍砖。