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); }
}
总结
JdbcTemplate类，附带了很多有用的重载查询方法。它提醒参考现有的查询方法在创建自己的自定义查询方法之前，因为 Spring 已经做给你了。