package dao;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

// 作用域

@Target({ ElementType.TYPE })

@Retention(RetentionPolicy.RUNTIME)

public @interface Table {

    String value();

}

 package dao;

 import java.lang.annotation.ElementType;

 import java.lang.annotation.Retention;

 import java.lang.annotation.RetentionPolicy;

 import java.lang.annotation.Target;

 // 作用域

 @Target({ ElementType.FIELD })

 @Retention(RetentionPolicy.RUNTIME)

 public @interface Column {

     String value();

 }

 package dao;

 /**

  *

  * 用户表，字段包括：用户ID、用户名、昵称、年龄、性别、所在城市、邮箱、手机号：

  *

  * @author  */

 @Table("user")

 public class User {

     @Column("id")

     private int id;

     @Column("user_name")

     private String userName;

     @Column("nick_name")

     private String nickName;

     @Column("age")

     private int age;

     @Column("city")

     private String city;

     @Column("email")

     private String email;

     @Column("mobile")

     private String mobile;

     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 String getNickName() {

         return nickName;

     }

     public void setNickName(String nickName) {

         this.nickName = nickName;

     }

     public int getAge() {

         return age;

     }

     public void setAge(int age) {

         this.age = age;

     }

     public String getCity() {

         return city;

     }

     public void setCity(String city) {

         this.city = city;

     }

     public String getEmail() {

         return email;

     }

     public void setEmail(String email) {

         this.email = email;

     }

     public String getMobile() {

         return mobile;

     }

     public void setMobile(String mobile) {

         this.mobile = mobile;

     }

 }

 package dao;

 import java.lang.reflect.Field;

 import java.lang.reflect.Method;

 /**

  * 根据参数动态返回查询语句

  *

  * @author  */

 public class ReturnQuery {

     public static String query(User u1) {

         StringBuilder str = new StringBuilder();

         // 1.获取一个类class

         Class c = u1.getClass();

         // 2.获取Table的名字

         boolean exists = c.isAnnotationPresent(Table.class);

         if (!exists) {

             return null;

         }

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

         String tableName = t.value();

         str.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取到字段名

             boolean fExists = field.isAnnotationPresent(Column.class);// 判断是否包含Column类型的注解

             if (!fExists) {

                 continue;

             }

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

             String columnName = column.value();

             // 4.2取到字段的值

             String fieldName = field.getName();

             // 获取相应字段的getXXX()方法

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

             Object fieldValue=null;

             try {

                 Method getMethod = c.getMethod(getMethodName);

                 fieldValue = getMethod.invoke(u1);

             } catch (Exception e) {

                 e.printStackTrace();

             }

             //4.3拼接Sql

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

                 continue;

             }

             str.append(" and ").append(fieldName);

             if (fieldValue instanceof String) {

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

                     String[] values=((String) fieldValue).split(",");

                     str.append(" in (");

                     for (String s : values) {

                         str.append("'").append(s).append("'").append(",");

                     }

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

                     str.append(")");

                 }else{

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

                 }

             }else {

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

             }

         }

         return str.toString();

     }

 }

 package dao;

 public class Test {

     public static void main(String[] args) {

         User u1 = new User();

         u1.setId(10); // 查询id

         User u2 = new User();

         u2.setUserName("JSFei"); // 模糊查询用户名

         u2.setAge(21);

         User u3 = new User();

         u3.setEmail("123@163.com,123@qq.com"); // 查询邮箱有任意一个的用户

         String sql1 = ReturnQuery.query(u1);

         String sql2 = ReturnQuery.query(u2);

         String sql3 = ReturnQuery.query(u3);

         System.out.println(sql1);

         System.out.println(sql2);

         System.out.println(sql3);

     }

 }