Java注解和反射练习

直接上代码了!

package com.merryyou.annotation;

import java.lang.annotation.*;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface Key {
}

package com.merryyou.annotation;

import java.lang.annotation.*;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface notRecord {
}

package com.merryyou.annotation;

import java.lang.annotation.*;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface Table {
    String name();
}

package com.merryyou.annotation;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
public class NumException extends Exception {
    private String name;

    public NumException(String message) {
        this.name = message;
    }

    public NumException(Throwable cause, String name) {
        super(name, cause);
        this.name = name;
    }

    public String toString(){
        return name;
    }
}

package com.merryyou.annotation;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
@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;
    }
}

package com.merryyou.annotation;

import java.lang.reflect.Field;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
public class Processing {

    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  返回 Field 对象的一个数组,这些对象反映此 Class 对象所表示的类或接口所声明的所有字段。
            boolean t=cl.getClass().isAnnotationPresent(Table.class);//获得类是否有注解 如果指定类型的注释存在于此元素上,则返回 true,否则返回 false。
            if(t){
                Table tab=cl.getClass().getAnnotation(Table.class);// 如果存在该元素的指定类型的注释,则返回这些注释,否则返回 null。
                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);//开启支持私有变量的访问权限
                    Object tobj=fl.get(cl);//返回指定对象上此 Field 表示的字段的值。
                    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;
    }
}

package com.merryyou.annotation;

/**
 * Created on 2016/10/31 0031.
 *
 * @author zlf
 * @since 1.0
 */
public class ProcessingTest {
    public static void main(String[] args) throws NumException, IllegalAccessException {
        Student student = new Student();
        student.setId("ccc");
        student.setName("姓名");
        student.setAge(18);
        student.setSex("男");
        System.out.println(new Processing().save(student));
    }
}

输出结果:

insert into student(id,name,age) values('ccc','姓名','18')

参考链接:
https://my.oschina.net/mfkwfc/blog/60885

共有 0 条评论

 Top