Spring JdbcTemplate查询示例

这里有一些示例向你展示如何使用JdbcTemplate的query()方法从数据库中查询或提取数据。

1. 查询单行

有两种可以从数据库中查询或提取一行数据，并将它们转换成一个model对象。

1.1 自定义RowMapper

通常，总是建议通过实现RowMapper接口来创建一个自定义的RowMapper类来满足你的需求，如下：

package com.mkyong.customer.model; import java.sql.ResultSet; import java.sql.SQLException; import org.springframework.jdbc.core.RowMapper; public class CustomerRowMapper implements RowMapper { public Object mapRow(ResultSet rs, int rowNum) throws SQLException { Customer customer = new Customer(); customer.setCustId(rs.getInt("CUST_ID")); customer.setName(rs.getString("NAME")); customer.setAge(rs.getInt("AGE")); return customer; } }

通过queryForObject()方法，返回的结果将调用你自定义得mapRow(...)方法以匹配正确的值，查询代码如下：

public Customer findByCustomerId(int custId){ String sql = "SELECT * FROM CUSTOMER WHERE CUST_ID = ?"; Customer customer = (Customer)getJdbcTemplate().queryForObject( sql, new Object[] { custId }, new CustomerRowMapper()); return customer; }

1.2 BeanPropertyRowMapper

在Spring 2.5中，有一个很方便的RowMapper接口的实现BeanPropertyRowMapper，它可以连续的将row value映射成一个property，只要它们具有相同的名称就行。比如：属性‘custId’将匹配列名‘CUSTID’或带下划线的‘CUST_ID’，查询代码如下：

public Customer findByCustomerId2(int custId){ String sql = "SELECT * FROM CUSTOMER WHERE CUST_ID = ?"; Customer customer = (Customer)getJdbcTemplate().queryForObject( sql, new Object[] { custId }, new BeanPropertyRowMapper(Customer.class)); return customer; }

2. 查询多行

现在，来看如何从数据库中查询或提取多行数据并转换到List容器中。

2.1 手动映射

在多行返回中，RowMapper不支持queryForList()方法，你需要手动的映射结果，如下：

public List<Customer> findAll(){ String sql = "SELECT * FROM CUSTOMER"; List<Customer> customers = new ArrayList<Customer>(); List<Map> rows = getJdbcTemplate().queryForList(sql); for (Map row : rows) { Customer customer = new Customer(); customer.setCustId((Long)(row.get("CUST_ID"))); customer.setName((String)row.get("NAME")); customer.setAge((Integer)row.get("AGE")); customers.add(customer); } return customers; }

2.2 BeanPropertyRowMapper

当然最简单的办法就是使用BeanPropertyRowMapper类。

public List<Customer> findAll(){ String sql = "SELECT * FROM CUSTOMER"; List<Customer> customers = getJdbcTemplate().query(sql, new BeanPropertyRowMapper(Customer.class)); return customers; }

2.3 使用自定义的RowMapper

当列名称与属性名称不一致时，也可以使用自定义的RowMapper类来替代BeanPropertyRowMapper。

public List<Customer> findAll(){ String sql = "SELECT * FROM CUSTOMER"; List<Customer> customers = getJdbcTemplate().query(sql, new CustomerRowMapper()); return customers; }

3. 查询单个值

在这个示例中，展示了如何从数据库中查询或提取一个单个列值。

3.1 单个列名称

它显示了如何查询String类型的名称为name列的单个值，如下：

public String findCustomerNameById(int custId){ String sql = "SELECT NAME FROM CUSTOMER WHERE CUST_ID = ?"; String name = (String)getJdbcTemplate().queryForObject( sql, new Object[] { custId }, String.class); return name; }

3.2 总行数

以下显示了如果从数据库中查询总行数：

public int findTotalCustomer(){ String sql = "SELECT COUNT(*) FROM CUSTOMER"; int total = getJdbcTemplate().queryForInt(sql); return total; }

Run it

package com.mkyong.common; import java.util.ArrayList; import java.util.List; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import com.mkyong.customer.dao.CustomerDAO; import com.mkyong.customer.model.Customer; public class JdbcTemplateApp { public static void main( String[] args ) { ApplicationContext context = new ClassPathXmlApplicationContext("Spring-Customer.xml"); CustomerDAO customerDAO = (CustomerDAO) context.getBean("customerDAO"); Customer customerA = customerDAO.findByCustomerId(1); System.out.println("Customer A : " + customerA); Customer customerB = customerDAO.findByCustomerId2(1); System.out.println("Customer B : " + customerB); List<Customer> customerAs = customerDAO.findAll(); for(Customer cust: customerAs){ System.out.println("Customer As : " + customerAs); } List<Customer> customerBs = customerDAO.findAll2(); for(Customer cust: customerBs){ System.out.println("Customer Bs : " + customerBs); } String customerName = customerDAO.findCustomerNameById(1); System.out.println("Customer Name : " + customerName); int total = customerDAO.findTotalCustomer(); System.out.println("Total : " + total); } }

总结

JdbcTemplate类中有许多有用的重载的查询方法，在你创建自定义的查询方法之前，建议先参考现有的查询方法，因为Spring可能意见维尼准备好了。

下载源码

Download it – Spring-JdbcTemplate-Querying-Example.zip (15 KB)

英文原文链接：http://www.mkyong.com/spring/spring-jdbctemplate-querying-examples/，略有增加。