這里有幾個例子向您展示如何使用JdbcTemplate的query()方法來查詢或從數據庫提取數據。整個項目的目錄結構如下：
1.查詢單行數據
這里有兩種方法來查詢或從數據庫中提取單行記錄，并將其轉換成一個模型類。
1.1 自定義RowMapper
在一般情況下，它總是建議實現 RowMapper 接口來創建自定義的RowMapper，以滿足您的需求。
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;
}
}
它傳遞給 queryForObject()方法，返回的結果將調用自定義 mapRow()方法的值匹配到屬性。
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，帶有一個方便 RowMapper 實現所謂“BeanPropertyRowMapper”，它可以通過匹配行的名字的列值映射到一個屬性。只要確保這兩個屬性和列具有相同的名稱，如屬性“CUSTID'將匹配到列名為：”CUSTID'或下劃線“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，查詢多行
現在，查詢或從數據庫中提取多行，并且將它轉換成一個列表。
2.1手動映射它
返回多行，RowMapper 不支持 queryForList()方法，需要手動映射它。
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
最簡單的解決方案是使用 BeanPropertyRowMapper 類。
public List<Customer> findAll(){
String sql = "SELECT * FROM CUSTOMER";
List<Customer> customers = getJdbcTemplate().query(sql,
new BeanPropertyRowMapper(Customer.class));
return customers;
}
3.查詢單值
在這個例子中，展示了如何從數據庫中查詢或提取單個列值。
3.1單列名
它顯示了如何查詢單個列名作為字符串。
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、行總數
它展示了如何從數據庫中查詢行的總數。
public int findTotalCustomer(){
String sql = "SELECT COUNT(*) FROM CUSTOMER";
int total = getJdbcTemplate().queryForInt(sql);
return total;
}
運行它
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);
}
}
總結
JdbcTemplate類，附帶了很多有用的重載查詢方法。它提醒參考現有的查詢方法在創建自己的自定義查詢方法之前，因為 Spring 已經做給你了。
