Spring--JdbcTemplate

JdbcTemplate简介

1. 为了使JDBC更加易于使用，Spring在JDBC API上定义了一个抽象层，以此建立一个JDBC存取框架
2. 作为Spring JDBC框架的核心，JDBC模板的设计目的是为不同类型的JDBC操作提供模板方法，每个模板方法都能控制整个过程，并允许覆盖过程中的特定任务。通过这种方式，可以在尽可能保留灵活性的情况下，将数据库存取的工作量降到最低。

代码示例：

首先是数据库的配置。数据库中包含employee和department两张表。

jdbc.user=scott
jdbc.password=tiger
jdbc.driverClass=oracle.jdbc.driver.OracleDriver
jdbc.jdbcUrl=jdbc:oracle:thin:@localhost:1521:orcl

jdbc.initialPoolSize=5
jdbc.maxPoolSize=10

然后是spring的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd">

    <context:component-scan base-package="com.yl.spring.jdbc"></context:component-scan>

    <!-- 导入属性文件 -->
    <context:property-placeholder location="classpath:db.properties"/>
    <!-- 配置c3p0数据源 -->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="user" value="${jdbc.user}"></property>
        <property name="password" value="${jdbc.password}"></property>
        <property name="driverClass" value="${jdbc.driverClass}"></property>
        <property name="jdbcUrl" value="${jdbc.jdbcUrl}"></property>
        
        <property name="initialPoolSize" value="${jdbc.initialPoolSize}"></property>
        <property name="maxPoolSize" value="${jdbc.maxPoolSize}"></property>
    </bean>

    <!-- 配置Spring的JdbcTemplate -->
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"></property>
    </bean>
</beans>

然后是两个实体类:Employee和Department

package com.yl.spring.jdbc;

public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    
    private Department department;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return "Employee [id=" + id + ", lastName=" + lastName + ", email="
                + email + ", department=" + department + "]";
    }
    
    
}

package com.yl.spring.jdbc;

public class Department {
    private Integer id;
    private String name;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Department [id=" + id + ", name=" + name + "]";
    }
    
    
}

然后是测试类

package com.yl.spring.jdbc;


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

import javax.sql.DataSource;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;

public class JDBCTest {
    
    private ApplicationContext ctx = null;
    private JdbcTemplate jdbcTemplate;
    private EmployeeDao employeeDao;
    
    {
        ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
        jdbcTemplate = (JdbcTemplate)ctx.getBean("jdbcTemplate");
        employeeDao = ctx.getBean(EmployeeDao.class);
    }
    
    @Test
    public void testEmployeeDao() {
        System.out.println(employeeDao.get(1));
    }
    
    /**
     * 获取单个列的值，或做统计查询
     */
    @Test
    public void testQueryForObject2() {
        String sql = "SELECT count(id) FROM employee";
        long count = jdbcTemplate.queryForObject(sql, Long.class);
        System.out.println(count);
    }
    
    /**
     * 查到实体类的集合
     */
    @Test
    public void testQueryForList() {
        String sql = "SELECT id, last_name, email FROM employee WHERE id > ?";
        RowMapper<Employee> rowMapper = new BeanPropertyRowMapper<Employee>(Employee.class);
        List<Employee> employees = jdbcTemplate.query(sql, rowMapper, 5);
        System.out.println(employees);
    }
    
    /**
     * 从数据库中获取一条记录，实际得到对应的一个对象
     * 1.RowMapper指定如何映射结果集的行，常用的实现类为BeanPropertyRowMapper
     * 2.使用SQL中列的别名完成列名和类的属性名的映射。例如last_name和lastName
     * 3.不支持级联属性。JdbcTemplate到底是一个JDBC工具，不是ORM框架。
     */
    @Test
    public void TestForQueryObject() {
        String sql = "SELECT id, last_name, email FROM employee WHERE id = ?";
        RowMapper<Employee> rowMapper = new BeanPropertyRowMapper<Employee>(Employee.class);
        
        Employee employee = jdbcTemplate.queryForObject(sql, rowMapper, 1);
        System.out.println(employee);
    }
    
    /**
     * 批量执行更新：批量的INSERT, UPDATE, DELETE
     * 最后一个参数是Object[]的list类型：因为修改一条记录需要一个Object的数组，那么多条就是需要多个Object的数组
     */
    @Test
    public void testBatchUpdate() {
        String sql = "INSERT INTO employee(id, last_name, email, dept_id) VALUES(?, ?, ?, ?)";
        List<Object[]> batchArgs = new ArrayList<Object[]>();
        batchArgs.add(new Object[]{6, "AA", "AA@163.com", 1});
        batchArgs.add(new Object[]{7, "BB", "BB@163.com", 2});
        batchArgs.add(new Object[]{8, "CC", "CC@163.com", 3});
        batchArgs.add(new Object[]{9, "DD", "DD@163.com", 3});
        batchArgs.add(new Object[]{10, "EE", "EE@163.com", 2});
        jdbcTemplate.batchUpdate(sql, batchArgs);
    }
    
    /**
     * 执行INSERT, UPDATE, DELETE
     */
    @Test
    public void testUpdate() {
        String sql = "UPDATE employee SET last_name=? WHERE id=?";
        jdbcTemplate.update(sql, "Jack", 5);
    }
    
    @Test
    public void test() throws SQLException {
        DataSource dataSource = (DataSource)ctx.getBean("dataSource");
        System.out.println(dataSource.getConnection());
    }

}

如果在项目中使用JdbcTemplate，那么可以参考下面的写法来写对应的dao：

package com.yl.spring.jdbc;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import org.springframework.stereotype.Repository;

@Repository
public class EmployeeDao {
    
    @Autowired
    private JdbcTemplate jdbcTemplate;
    
    public Employee get(Integer id) {
        String sql = "SELECT id, last_name, email FROM employee WHERE id = ?";
        RowMapper<Employee> rowMapper = new BeanPropertyRowMapper<Employee>(Employee.class);
        
        Employee employee = jdbcTemplate.queryForObject(sql, rowMapper, id);
        
        return employee;
    }
}