Spring JdbcTemplate查询实例

Posted 2020-08-29 左正

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。

 

下载代码 –  http://pan.baidu.com/s/1gecQHmN