16、JDBC-DBUtils封装

使用DBUtils写个通用CURD小工具

依赖配置

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>yofc</groupId>
    <artifactId>jdbc</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.15</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.14</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-nop</artifactId>
            <version>1.7.26</version>
        </dependency>
        <dependency>
            <groupId>commons-dbutils</groupId>
            <artifactId>commons-dbutils</artifactId>
            <version>1.7</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <!-- 指定jdk -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

druid.properties

username=root
password=root
url=jdbc:mysql://192.168.8.136:3306/jdbc
driverClassName=com.mysql.cj.jdbc.Driver

接口

package com.jdbc.dao;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

/**
 * 访问数据的 DAO 接口
 * @param <T> DAO 处理的实体类的类型
 */
public interface DAO<T> {

    /**
     * 批量处理的方法
     * @param args: 填充占位符的参数
     */
    void batch(Connection connection, String sql, Object[]... args) throws SQLException;

    /**
     * 返回具体的一个值,
     */
    <E> E getForValue(Connection connection, String sql, Object... args) throws SQLException;

    /**
     * 返回 T 的一个集合
     */
    List<T> getForList(Connection connection, String sql, Object... args) throws SQLException;

    /**
     * 返回一个 T 的对象
     */
    T get(Connection connection, String sql, Object... args) throws SQLException;

    /**
     * INSRET, UPDATE, DELETE 方法
     * @param connection: 数据库连接
     * @param sql:        SQL 语句
     * @param args:       填充占位符的可变参数
     * @throws SQLException
     */
    void update(Connection connection, String sql, Object... args) throws SQLException;
}

JDBC的实现

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;

import com.jdbc.dao.DAO;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;

/**
 * 使用 QueryRunner 提供其具体的实现
 * @param <T>: 子类需传入的泛型类型.
 */
public class JdbcDaoImpl<T> implements DAO<T> {

    private QueryRunner queryRunner = null;
    private Class<T> type;

    /**
     * 通过反射获得定义 Class 时声明的父类的泛型参数的类型
     */
    public static Class getSuperClassGenricType(Class clazz, int index) {
        Type genType = clazz.getGenericSuperclass();
        if (!(genType instanceof ParameterizedType)) {
            return Object.class;
        }
        Type[] params = ((ParameterizedType) genType).getActualTypeArguments();
        if (index >= params.length || index < 0) {
            return Object.class;
        }
        if (!(params[index] instanceof Class)) {
            return Object.class;
        }
        return (Class) params[index];
    }

    public JdbcDaoImpl() {
        queryRunner = new QueryRunner();
        type = getSuperClassGenricType(getClass(),0);
    }

    @Override
    public void batch(Connection connection, String sql, Object[]... args) throws SQLException {
        queryRunner.batch(connection, sql, args);
    }

    @Override
    public <E> E getForValue(Connection connection, String sql, Object... args) throws SQLException {
        return (E) queryRunner.query(connection, sql, new ScalarHandler(), args);
    }

    @Override
    public List<T> getForList(Connection connection, String sql, Object... args) throws SQLException {
        return queryRunner.query(connection, sql, new BeanListHandler<>(type), args);
    }

    @Override
    public T get(Connection connection, String sql, Object... args) throws SQLException {
        return queryRunner.query(connection, sql, new BeanHandler<>(type), args);
    }

    @Override
    public void update(Connection connection, String sql, Object... args) throws SQLException {
        queryRunner.update(connection, sql, args);
    }
}

数据连接池

package com.jdbc.utils;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import javax.sql.DataSource;
import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class DruidDataPoolUtils {

    private static Properties properties;
    private static DataSource dataSource;

    static {
        try {
            properties = new Properties();
            properties.load(DruidDataPoolUtils.class.getClassLoader().getResourceAsStream("druid.properties"));
            dataSource = DruidDataSourceFactory.createDataSource(properties);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static Connection getConnection() {
        try {
            return dataSource.getConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 注意参数顺序
     * 开始：ResultSet
     * 中间：Statement、PreparedStatement、CallableStatement
     * 最后：Connection
     *
     * @param closed
     */
    public static void close(Object... closed) {
        try {
            for (Object object : closed) {
                if (object instanceof ResultSet) {
                    ((ResultSet) object).close();
                } else if (object instanceof Statement) {
                    ((Statement) object).close();
                } else if (object instanceof Connection) {
                    ((Connection) object).close();
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

测试

UserDao

public class UserDao extends JdbcDaoImpl<User> {
}

Main

public static void main(String[] args) throws SQLException {
    UserDao userDao = new UserDao();
    Connection connection = null;
    try {
        connection = DruidDataPoolUtils.getConnection();
        String sql = "select * from user WHERE id = ?";
        User user = userDao.get(connection, sql, 19);
        System.out.println(user);
    } catch (Exception e) {
        e.printStackTrace();
    } finally{
        DruidDataPoolUtils.close(connection);
    }
}

项目结构

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https://k1121.iteye.com/blog/1279063