Spring JDBC - 读取查询

---

---

概述

下面的例子将演示如何使用 Spring JDBC 读取查询。我们将读取学生表中的可用记录。

语法

String selectQuery = "select * from Student";
List <Student> students = jdbcTemplateObject.query(selectQuery, new StudentMapper());

其中：

• selectQuery − 读取学生的查询语句。

• jdbcTemplateObject − 从数据库读取学生对象的 StudentJDBCTemplate 对象。

• StudentMapper − StudentMapper 是一个 RowMapper 对象，用于将每个提取的记录映射到学生对象。

示例

为了理解上面提到的与 Spring JDBC 相关的概念，让我们编写一个将选择查询的示例。为了编写我们的示例，让我们准备好一个可用的 Eclipse IDE，并使用以下步骤创建一个 Spring 应用程序。

StudentDAO.java

以下是数据访问对象接口文件 StudentDAO.java 的内容。

package com.tutorialspoint;

import java.util.List;
import javax.sql.DataSource;

public interface StudentDAO {
   /** 
    * This is the method to be used to initialize
    * database resources ie. connection.
   */
   public void setDataSource(DataSource ds);
   
   /** 
    * This is the method to be used to list down
    * all the records from the Student table.
   */
   public List<Student> listStudents();   
}

Student.java

以下是 Student.java 文件的内容。

package com.tutorialspoint;

// Student POJO for Student Table
public class Student {
   private Integer age;
   private String name;
   private Integer id;

   // setter/getter methods
   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      return age;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
   public void setId(Integer id) {
      this.id = id;
   }
   public Integer getId() {
      return id;
   }
}

StudentMapper.java

以下是 StudentMapper.java 文件的内容。

package com.tutorialspoint;

import java.sql.ResultSet;
import java.sql.SQLException;
import org.springframework.jdbc.core.RowMapper;

// Row Mapper Object to map Student table entry with Student Object
public class StudentMapper implements RowMapper<Student> {
   public Student mapRow(ResultSet rs, int rowNum) throws SQLException {
      Student student = new Student();
      student.setId(rs.getInt("id"));
      student.setName(rs.getString("name"));
      student.setAge(rs.getInt("age"));
      return student;
   }
}

StudentJDBCTemplate.java

以下是为定义的 DAO 接口 StudentDAO 编写的实现类文件 StudentJDBCTemplate.java。

package com.tutorialspoint;

import java.util.List;
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;

// DAO instance to persist Student values
public class StudentJDBCTemplate implements StudentDAO {
   private DataSource dataSource;
   private JdbcTemplate jdbcTemplateObject;
   
   // set the datasource and jdbctemplate
   public void setDataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      this.jdbcTemplateObject = new JdbcTemplate(dataSource);
   }
   
   // get all the students from the database
   public List<Student> listStudents() {
      String SQL = "select * from Student";
      List <Student> students = jdbcTemplateObject.query(SQL, new StudentMapper());
      return students;
   }
}

MainApp.java

以下是 MainApp.java 文件的内容。

package com.tutorialspoint;

import java.util.List;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.tutorialspoint.StudentJDBCTemplate;

public class MainApp {
   public static void main(String[] args) {
   
      // Create the application context by reading Beans.xml      
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
	  
      // Create the JDBCTemplate instance from spring context 
      StudentJDBCTemplate studentJDBCTemplate = (StudentJDBCTemplate)context.getBean("studentJDBCTemplate");
      
      // get all the students
      System.out.println("------Listing Multiple Records--------" );
      List<Student> students = studentJDBCTemplate.listStudents();
      
      // print all the students
      for (Student record : students) {
         System.out.print("ID : " + record.getId() );
         System.out.print(", Name : " + record.getName() );
         System.out.println(", Age : " + record.getAge());
      }  
   }
}

Beans.xml

以下是配置文件 Beans.xml。

<?xml version = "1.0" encoding = "UTF-8"?>
<beans xmlns = "http://www.springframework.org/schema/beans"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" 
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd ">

   <!-- Initialization for data source -->
   <bean id = "dataSource" 
      class = "org.springframework.jdbc.datasource.DriverManagerDataSource">
      <property name = "driverClassName" value = "com.mysql.cj.jdbc.Driver"/>
      <property name = "url" value = "jdbc:mysql://:3306/TEST"/>
      <property name = "username" value = "root"/>
      <property name = "password" value = "admin"/>
   </bean>

   <!-- Definition for studentJDBCTemplate bean -->
   <bean id="studentJDBCTemplate" 
      class = "com.tutorialspoint.StudentJDBCTemplate">
      <property name = "dataSource" ref = "dataSource" />    
   </bean>
</beans>

输出

创建源文件和 bean 配置文件后，让我们运行该应用程序。如果应用程序一切正常，它将打印以下消息。

------Listing Multiple Records--------
ID : 1, Name : Zara, Age : 11
ID : 2, Name : Nuha, Age : 2
ID : 3, Name : Ayan, Age : 15