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Spring JdbcTemplate Querying examples

2017-03-17 18:54

Spring JdbcTemplate Querying examples

2017-03-17 18:54

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。

CSDN同步地址:http://blog.csdn.net/t894690230/article/details/60882891