Spring JdbcTemplate查询实例

这里有几个例子向您展示如何使用JdbcTemplate的query()方法来查询或从数据库提取数据。整个项目的目录结构如下：

1.查询单行数据

这里有两种方法来查询或从数据库中提取单行记录，并将其转换成一个模型类。

1.1 自定义RowMapper

在一般情况下，它总是建议实现 RowMapper 接口来创建自定义的RowMapper，以满足您的需求。

package com.yiibai.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;}}

它传递给 queryForObject()方法，返回的结果将调用自定义 mapRow()方法的值匹配到属性。

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Spring2.5中，带有一个方便 RowMapper 实现所谓“BeanPropertyRowMapper”，它可以通过匹配行的名字的列值映射到一个属性。只要确保这两个属性和列具有相同的名称，如属性“CUSTID'将匹配到列名为：”CUSTID'或下划线“CUST_ID”。

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，查询或从数据库中提取多行，并且将它转换成一个列表。

2.1手动映射它

返回多行，RowMapper 不支持 queryForList()方法，需要手动映射它。

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

最简单的解决方案是使用 BeanPropertyRowMapper 类。

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

3.查询单值

在这个例子中，展示了如何从数据库中查询或提取单个列值。

3.1单列名

它显示了如何查询单个列名作为字符串。

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、行总数

它展示了如何从数据库中查询行的总数。

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

运行它

package com.yiibai.common;import java.util.ArrayList;
import java.util.List;import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.yiibai.customer.dao.CustomerDAO;
import com.yiibai.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);}
}