package com.hk.test;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Target({ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

public @interface Table {

    String value();

}

package com.hk.test;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Target({ElementType.FIELD})

@Retention(RetentionPolicy.RUNTIME)

public @interface Column {

    String value();

}

package com.hk.test;

@Table("user")

public class Filter {

    @Column("id")

    private int id;

    @Column("user_name")

    private String userName;

    @Column("age")

    private int age;

    @Column("email")

    private String email;

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getUserName() {

        return userName;

    }

    public void setUserName(String userName) {

        this.userName = userName;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

    public String getEmail() {

        return email;

    }

    public void setEmail(String email) {

        this.email = email;

    }

}

package com.hk.test;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

/**

 *

 * @author hk_z

 * @deprecated 对类进行反射 获取注解和字段名 拼接成sql语句

 * @version 0.1

 */

public class Test {

    public static void main(String[] args) {

        Filter f1 = new Filter();

        f1.setId(10);

        Filter f2 = new Filter();

        f2.setUserName("lucy"); //模糊查询

        Filter f3 = new Filter();

        f3.setEmail("zhangsan@qq.com,lisi@sina.com.cn"); //任意其一

        String sql1 =query(f1);

        System.out.println(sql1);

        String sql2 =query(f2);

        System.out.println(sql2);

        String sql3 =query(f3);

        System.out.println(sql3);

    }

    private static String query(Filter f1) {

        // TODO Auto-generated method stub

        StringBuilder sb =new StringBuilder();

        //1.获取到class

        Class c = f1.getClass();

        //2.获取到table 的名字

        boolean exists = c.isAnnotationPresent(Table.class); //class 中有没有table的注解

        if(!exists){

            return null;

        }

        Table t= (Table)c.getAnnotation(Table.class);

        String tableName = t.value(); //表名

        sb.append("select * from ").append(tableName).append(" where 1 = 1");

        //3.遍历所有的字段

        Field[] fArray = c.getDeclaredFields();

        for(Field field:fArray){

            //4.处理每个字段对应的sql

            //4.1 拿到字段名

            boolean fExists = field.isAnnotationPresent(Column.class);

            if(!fExists){

                continue;

            }

            Column column = field.getAnnotation(Column.class);

            String columnName = column.value();  //表里面字段的名字

            //4.2拿到字段的值

            String filedName = field.getName(); //变量的名字

            String getMethodName = "get"+filedName.substring(0,1).toUpperCase()+filedName.substring(1);

            Object fieldValue = null;

            //拼装get方法 获取返回值 ；

            try {

                Method getMethod = c.getMethod(getMethodName); //反射

                fieldValue = getMethod.invoke(f1);     //反射调用    

            } catch (Exception e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            //4.3 拼装sql

            if(fieldValue == null||(fieldValue instanceof Integer &&(Integer)fieldValue==0))

            {

                continue;

            }

            sb.append(" and ").append(filedName);

            String [] val=null;

            if(fieldValue instanceof String){ //字串型并且有逗号 进行拆分

                if(((String)fieldValue).contains(",")){

                    val = ((String) fieldValue).split(",");

                    sb.append(" in(");

                    for(String v:val){

                        sb.append("'").append(v).append("'").append(",");

                    }

                    sb.deleteCharAt(sb.length()-1);

                    sb.append(")");

                    }

                else{

                    sb.append(" = ").append("'").append(fieldValue).append("'");

                }

            }

            else if(fieldValue instanceof Integer){

            sb.append(" = ").append(fieldValue);

            }

        }

        return sb.toString();

    }

}