java注解和反射制作dao基类的练习

Posted 2020-07-24

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));
    }
}