Springjdbc 简明教程

Spring JDBC - ResultSetExtractor Interface

org.springframework.jdbc.core.ResultSetExtractor 接口是 JdbcTemplate 的查询方法使用的回调接口。此接口的实现执行从 ResultSet 中提取结果的实际工作，但不必担心异常处理。

The org.springframework.jdbc.core.ResultSetExtractor interface is a callback interface used by JdbcTemplate’s query methods. Implementations of this interface perform the actual work of extracting results from a ResultSet, but don’t need to worry about exception handling.

SQLException 将由调用的 JdbcTemplate 捕获并处理。此界面主要用于 JDBC 框架本身中。RowMapper 通常是 ResultSet 处理的一个更简单的选择，它为每行映射一个结果对象，而不是为整个 ResultSet 映射一个结果对象。

SQLExceptions will be caught and handled by the calling JdbcTemplate. This interface is mainly used within the JDBC framework itself. A RowMapper is usually a simpler choice for ResultSet processing, mapping one result object per row instead of one result object for the entire ResultSet.

Interface Declaration

以下是 org.springframework.jdbc.core.ResultSetExtractor 接口的声明 −

Following is the declaration for org.springframework.jdbc.core.ResultSetExtractor interface −

public interface ResultSetExtractor

Usage

  1. Step 1 − Create a JdbcTemplate object using a configured datasource.

  2. Step 2 − Use JdbcTemplate object methods to make database operations while parsing the resultset using ResultSetExtractor.

Example

以下示例将演示如何使用 JdbcTemplate 类和 ResultSetExtractor 接口读取查询。我们将读取 Student 表中学生的可用记录。

Following example will demonstrate how to read a query using JdbcTemplate class and ResultSetExtractor interface. We’ll read available record of a student in Student Table.

Syntax

public List<Student> listStudents() {
   String SQL = "select * from Student";
   List <Student> students = jdbcTemplateObject.query(
      SQL, new ResultSetExtractor<List<Student>>(){
         public List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> list = new ArrayList<Student>();
            while(rs.next()){
               Student student = new Student();
               student.setId(rs.getInt("id"));
               student.setName(rs.getString("name"));
               student.setAge(rs.getInt("age"));
               student.setDescription(rs.getString("description"));
               student.setImage(rs.getBytes("image"));
               list.add(student);
            }
            return list;
         }
      }
   );
   return students;
}

其中，

Where,

  1. SQL − Select query to read students.

  2. jdbcTemplateObject − StudentJDBCTemplate object to read student object from database.

  3. ResultSetExtractor − ResultSetExtractor object to parse resultset object.

为了理解与 Spring JDBC 相关的上述概念，我们编写一个将选择一个查询的示例。为了编写我们的示例，让我们有一个可用的 Eclipse IDE 并使用以下步骤创建一个 Spring 应用程序。

To understand the above-mentioned concepts related to Spring JDBC, let us write an example which will select a query. To write our example, let us have a working Eclipse IDE in place and use the following steps to create a Spring application.

Step

Description

1

Update the project Student created under chapter Spring JDBC - First Application.

2

Update the bean configuration and run the application as explained below.

以下是对数据访问对象接口文件 StudentDAO.java 的内容。

Following is the content of the Data Access Object interface file StudentDAO.java.

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();
}

以下是 Student.java 文件的内容。

Following is the content of the Student.java file.

package com.tutorialspoint;

public class Student {
   private Integer age;
   private String name;
   private Integer id;

   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;
   }
}

以下是对所定义的 DAO 接口 StudentDAO 实现的类文件 StudentJDBCTemplate.java 。

Following is the implementation class file StudentJDBCTemplate.java for the defined DAO interface StudentDAO.

package com.tutorialspoint;

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

public class StudentJDBCTemplate implements StudentDAO {
   private DataSource dataSource;
   private JdbcTemplate jdbcTemplateObject;

   public void setDataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      this.jdbcTemplateObject = new JdbcTemplate(dataSource);
   }
   public List<Student> listStudents() {
      String SQL = "select * from Student";
      List <Student> students = jdbcTemplateObject.query(SQL,
         new ResultSetExtractor<List<Student>>(){
         public List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> list = new ArrayList<Student>();
            while(rs.next()){
               Student student = new Student();
               student.setId(rs.getInt("id"));
               student.setName(rs.getString("name"));
               student.setAge(rs.getInt("age"));
               student.setDescription(rs.getString("description"));
               student.setImage(rs.getBytes("image"));
               list.add(student);
            }
            return list;
         }
      });
      return students;
   }
}

以下是 MainApp.java 文件的内容。

Following is the content of the MainApp.java file.

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
      StudentJDBCTemplate studentJDBCTemplate = (StudentJDBCTemplate)context.getBean("studentJDBCTemplate");
      List<Student> students = studentJDBCTemplate.listStudents();

      for(Student student: students){
         System.out.print("ID : " + student.getId() );
         System.out.println(", Age : " + student.getAge());
      }
   }
}

以下是配置文件 Beans.xml 。

Following is the configuration file 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://localhost: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>

一旦您完成创建源代码和 bean 配置文件，让我们运行此应用程序。如果应用程序一切正常，它将打印以下信息。

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message.

ID : 1, Age : 17
ID : 3, Age : 18