这里有几个例子来说明如何使用SimpleJdbcTemplate query()方法来查询或从数据库中提取数据。在 JdbcTemplate query() 方法，需要手动转换返回的结果转换为一个目标对象类型，并传递一个对象数组作为参数。在SimpleJdbcTemplate类，它是更加人性化和简单。
1.查询单行
这里有向你展示了如何查询或从数据库中提取单行的两种方式，并将其转换成一个模型类。
1.1 自定义RowMapper
在一般情况下，它总是建议来实现 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;
}
}
public Customer findByCustomerId(int custId){
String sql = "SELECT * FROM CUSTOMER WHERE CUST_ID = ?";
Customer customer = getSimpleJdbcTemplate().queryForObject(
sql, new CustomerParameterizedRowMapper(), custId);
return customer;
}
1.2 BeanPropertyRowMapper
在SimpleJdbcTemplate类，需要使用“ParameterizedBeanPropertyRowMapper' 代替 'BeanPropertyRowMapper”。
public Customer findByCustomerId2(int custId){
String sql = "SELECT * FROM CUSTOMER WHERE CUST_ID = ?";
Customer customer = getSimpleJdbcTemplate().queryForObject(sql,
ParameterizedBeanPropertyRowMapper.newInstance(Customer.class), custId);
return customer;
}
2，查询多行
从数据库查询或提取多行记录，并将其转换成一个列表。
2.1 ParameterizedBeanPropertyRowMapper
public List<Customer> findAll(){
String sql = "SELECT * FROM CUSTOMER";
List<Customer> customers =
getSimpleJdbcTemplate().query(sql,
ParameterizedBeanPropertyRowMapper.newInstance(Customer.class));
return customers;
}
3.查询单值
查询或提取数据库中的单个列的值。
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 = getSimpleJdbcTemplate().queryForObject(
sql, String.class, custId);
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 = getSimpleJdbcTemplate().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 SimpleJdbcTemplateApp
{
public static void main( String[] args )
{
ApplicationContext context =
new ClassPathXmlApplicationContext("Spring-Customer.xml");
CustomerDAO customerSimpleDAO =
(CustomerDAO) context.getBean("customerSimpleDAO");
Customer customerA = customerSimpleDAO.findByCustomerId(1);
System.out.println("Customer A : " + customerA);
Customer customerB = customerSimpleDAO.findByCustomerId2(1);
System.out.println("Customer B : " + customerB);
List<Customer> customerAs = customerSimpleDAO.findAll();
for(Customer cust: customerAs){
System.out.println("Customer As : " + customerAs);
}
List<Customer> customerBs = customerSimpleDAO.findAll2();
for(Customer cust: customerBs){
System.out.println("Customer Bs : " + customerBs);
}
String customerName = customerSimpleDAO.findCustomerNameById(1);
System.out.println("Customer Name : " + customerName);
int total = customerSimpleDAO.findTotalCustomer();
System.out.println("Total : " + total);
}
}
总结
SimpleJdbcTemplate 是不能代替 JdbcTemplate 的，它只是一个Java5的友好补充它。
