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queryForObject:返回一个对象
一、Spring中的RowMapper
sping中的RowMapper可以将数据中的每一行数据封装成用户定义的类
我们在数据库查询中,如果返回的类型是用户自定义的类型(其实我们在数据库查询中大部分返回的都是自定义的类)则需要包装,如果是Java自定义的类型,如:String。
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.gp6.jdbc.template.rowMapper.bean;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.springframework.jdbc.core.RowMapper;
@SuppressWarnings("rawtypes")
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;
}
二、 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;
}
三、query返回一个集合
/**
* 功能:查询返回对象集合
* 步骤:新建MyRowMapper类实现RowMapper接口,重写mapRow方法,指定返回User对象
*/
public static void queryForList(JdbcTemplate jdbcTemplate) {
String sql = "select * from user";
// 第三个参数可以省略
List<User> users = jdbcTemplate.query(sql, new MyRowMapper());
System.out.println(users);
}
四、queryForList返回一个集合 (但不支持 RowMapper),所以获得list列表后,要手动映射
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;
}
五、BeanPropertyRowMapper获取多行数据
public List<Customer> findAll(){
String sql = "SELECT * FROM CUSTOMER";
List<Customer> customers = getJdbcTemplate().query(sql,
new BeanPropertyRowMapper(Customer.class));
return customers;
}
六、查询单值
单列名
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;
}