仿Mybatis手撸注解SQL实现DAO接口(下)——动态代理的使用—

需求

上一篇我们对JDBC进行了简单的封装，主要实现了对结果集和java bean的映射。现在我们需要通过代理调用封装好的DBUtils动态实现DAO接口

定义增删改查注解@Insert, @Delete, @Update, @Select

以下四个注解

@Target(ElementType.METHOD) 指定注解的作用目标为Method
@Retention(RetentionPolicy.RUNTIME) 指定注解的作用域为Runtime,即可
以在JVM通过反射获取该注解的信息
四个注解都有一个value属性，用于保存sql

// Insert.java
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Insert {
  String value();
}

// Delete.java
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Delete {
  String value();
}

// Update.java
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Update {
  String value();
}

// Select.java
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Select {
  String value();
}

通过动态代理实现接口

Java动态代理 Proxy.newProxyInstance(Interface, Class[],InvocationHandler)
自定义SQLInvocationHandler来实现对标准过SQL注解的Method解析并调用相应DBUtils的方法来实现接口方法
- 使用@Select的接口，首先判断其返回类型是否存在泛型（说明肯定不是基本类型）
  - 如果存在泛型，目前只支持返回List,调用DBUtils.selectList()方法实现
  - 如果不存在泛型，判断是否为基本类型，如果是基本类型，说明查询的是单列，调用DButils.selectValue()实现。如果不是基本类型，调用DBUtils.selectOne()方法实现
- 使用@Insert, @Update, @Delete的接口，调用DBUtils.execute()方法实现

public class ProxyFactory {
  public static Object proxyMapper(Class<?>... clazz) {
    return Proxy.newProxyInstance(ProxyFactory.class.getClassLoader(), clazz, new SQLInvocationHandler());
  }

  // 代理接口
  private static class SQLInvocationHandler implements InvocationHandler {

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      DBUtils dbUtils = DBUtils.getInstance();
      Connection connection = dbUtils.getConnection();
      // 检查Select注解
			if (method.isAnnotationPresent(Select.class)) {
        Select one = method.getAnnotation(Select.class);
        String sql = one.value();

        Type returnType = method.getGenericReturnType();
        // 判断返回类型是否存在泛型
        if (returnType instanceof ParameterizedType) {
          ParameterizedType actualType = (ParameterizedType) returnType;
          // 集合支持List
          if (actualType.getRawType().equals(List.class)) {
            // 获取泛型的类型
            Class<?> mapperType = (Class<?>)actualType.getActualTypeArguments()[0];
            return dbUtils.selectList(connection, mapperType, sql, args);
          }
          throw new RuntimeException("Unsupported Return Type: " + method.toString());
        }
        // 不存在泛型
        Class<?> clazz = (Class<?>)returnType;
        if (ReflectUtil.isPrimaryType(clazz)){
          // 基本类型
          return dbUtils.selectValue(connection, clazz, sql, args);
        } else {
          return dbUtils.selectOne(connection, clazz, sql, args);
        }
      } else if (method.isAnnotationPresent(Update.class)) {
        // 处理Update
        Update update = method.getAnnotation(Update.class);
        return dbUtils.execute(connection, update.value(), args);
      } else if (method.isAnnotationPresent(Delete.class)) {
        // 处理Delete
        Delete delete = method.getAnnotation(Delete.class);
        return dbUtils.execute(connection, delete.value(), args);
      } else if (method.isAnnotationPresent(Insert.class)) {
        // 处理Insert
        Insert insert = method.getAnnotation(Insert.class);
        return dbUtils.execute(connection, insert.value(), args);
      }
			return null;
    }  
  }
}

使用ProxyFactory动态代理一个DAO接口

准备数据

CREATE DATABASE /*!32312 IF NOT EXISTS*/ `test` /*!40100 DEFAULT CHARACTER SET utf8mb4 */;
USE `test`;
DROP TABLE IF EXISTS `t_student`;
CREATE TABLE `t_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'primary key',
  `created_time` datetime DEFAULT NULL COMMENT 'created time',
  `updated_time` datetime DEFAULT NULL COMMENT 'updated time',
  `name` varchar(20) DEFAULT NULL COMMENT '姓名',
  `birthday` date DEFAULT NULL COMMENT '生日',
  `address` varchar(200) DEFAULT NULL COMMENT '家庭住址',
  `phone` varchar(20) DEFAULT NULL COMMENT '联系方式',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 COMMENT='学生信息表';

INSERT INTO `t_student` (`id`,`created_time`,`updated_time`,`name`,`birthday`,`address`,`phone`)
VALUES (2,'2020-11-03 11:43:06','2020-11-03 11:43:06','李自成','2000-05-01','广东韶关','177888888'),
(3,'2020-11-03 11:43:06','2020-11-03 11:43:06','王老五','2002-03-01','江苏南京','199888888'),
(4,'2020-11-03 11:43:06','2020-11-03 11:43:06','葛二蛋','2000-12-01','四川成都','166888888'),
(5,'2020-11-03 02:15:31','2020-11-03 02:15:31','赵四','2000-03-01','新疆乌鲁木齐','166666666'),
(6,'2020-11-25 17:17:44','2020-11-25 17:17:44','???','2020-11-25','????','13333333333'),
(7,'2020-11-25 17:20:18','2020-11-25 17:20:18','牛夫人','2020-11-25','四川成都','13333333333'),
(8,'2020-11-26 10:42:31','2020-11-26 10:42:31','蒋某','2020-11-26','广东东莞','1234322112');

对应t_student表的Java bean

package com.yeyeck.yebatis.test;

import java.time.LocalDate;
import java.time.LocalDateTime;
import lombok.Data;

@Data
public class Student {
  private Integer id;
  private String name;
  private LocalDate birthday;
  private String address;
  private String phone;
  private LocalDateTime createdTime;
  private LocalDateTime updatedTime;
}

HikariCP 配置

jdbcUrl=jdbc:mysql://localhost:3306/test?characterEncoding=utf8
username=root
password=password
dataSource.cachePrepStmts=true
dataSource.prepStmtCacheSize=250
dataSource.prepStmtCacheSqlLimit=2048
dataSource.useServerPrepStmts=true
dataSource.useLocalSessionState=true
dataSource.rewriteBatchedStatements=true
dataSource.cacheResultSetMetadata=true
dataSource.cacheServerConfiguration=true
dataSource.elideSetAutoCommits=true
dataSource.maintainTimeStats=false

定义接口StudentDao

import java.time.LocalDate;
import java.util.List;

import com.yeyeck.yebatis.annotation.Delete;
import com.yeyeck.yebatis.annotation.Insert;
import com.yeyeck.yebatis.annotation.Select;
import com.yeyeck.yebatis.annotation.Update;

public interface StudentDao {
  @Select("select * from t_student where id = ?")
  Student findById(Integer id);

  @Select("select * from t_student")
  List<Student> findAll();

  @Select("select count(id) from t_student")
  Integer countAll();

  @Update("update t_student set name = ? where id = ?")
  int updateName(String name, Integer id);

  @Insert("insert into t_student(name, birthday, address, phone, created_time, updated_time)" + 
           "values (?, ?, ?, ?, now(), now())")
  int addStudent(String name, LocalDate birthday, String address, String phone);

  @Delete("delete from t_student where id = ?")
  int removeById(Integer id);

  @Select("select birthday from t_student where id = ?")
  LocalDate findBirthdayById(Integer id);

  @Select("select name from t_student")
  List<String> findAllNames();
  
}

使用动态代理实现StudentDao接口

    // 代理接口
    StudentDao studentDao = (StudentDao)ProxyFactory.proxyMapper(StudentDao.class);
    // 使用接口
    List<Student> students = studentDao.findAll();
    System.out.println(students);