Spring JDBC - 处理BLOB

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概述

以下示例将演示如何使用更新查询和Spring JDBC来更新BLOB。我们将更新Student表中的可用记录。

学生表

CREATE TABLE Student(
   ID INT NOT NULL AUTO_INCREMENT,
   NAME VARCHAR(20) NOT NULL,
   AGE INT NOT NULL,
   IMAGE BLOB,
   PRIMARY KEY (ID)
);

语法

MapSqlParameterSource in = new MapSqlParameterSource();
in.addValue("id", id);
in.addValue("image",  new SqlLobValue(new ByteArrayInputStream(imageData), 
   imageData.length, new DefaultLobHandler()), Types.BLOB);

String SQL = "update Student set image = :image where id = :id";
NamedParameterJdbcTemplate jdbcTemplateObject = new NamedParameterJdbcTemplate(dataSource);
jdbcTemplateObject.update(SQL, in);

其中，

• in − SqlParameterSource对象，用于传递参数以更新查询。

• SqlLobValue − 表示SQL BLOB/CLOB值参数的对象。

• jdbcTemplateObject − NamedParameterJdbcTemplate对象，用于更新数据库中的学生对象。

示例

为了理解上面提到的与Spring JDBC相关的概念，让我们编写一个示例，该示例将更新查询。为了编写我们的示例，让我们准备一个可用的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 update
    * a record into the Student table.
   */
   public void updateImage(Integer id, byte[] imageData);
}

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;
   private byte[] image;

   // 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;
   }
   public byte[] getImage() {
      return image;
   }
   public void setImage(byte[] image) {
      this.image = image;
   }
}

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"));
      student.setImage(rs.getBytes("image"));
      return student;
   }
}

StudentJDBCTemplate.java

以下是为已定义的DAO接口StudentDAO实现的类文件StudentJDBCTemplate.java。

package com.tutorialspoint;

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

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.namedparam.MapSqlParameterSource;
import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
import org.springframework.jdbc.core.namedparam.SqlParameterSource;
import org.springframework.jdbc.core.simple.SimpleJdbcCall;
import org.springframework.jdbc.core.support.SqlLobValue;
import org.springframework.jdbc.support.lob.DefaultLobHandler;
import java.io.ByteArrayInputStream;
import java.sql.Types;

// 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 NamedParameterJdbcTemplate(dataSource);
   }
   
   // update the image based on id
   public void updateImage(Integer id, byte[] imageData) {
      MapSqlParameterSource in = new MapSqlParameterSource();
      in.addValue("id", id);
      in.addValue("image",  new SqlLobValue(new ByteArrayInputStream(imageData), 
         imageData.length, new DefaultLobHandler()), Types.BLOB);

      String SQL = "update Student set image = :image where id = :id";
      
      jdbcTemplateObject.update(SQL, in);
      System.out.println("Updated Record with ID = " + id );
   }
}

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");

      // create an image data      
      byte[] imageData = {0,1,0,8,20,40,95};
      // persist the image
      studentJDBCTemplate.updateImage(1, imageData);  
   }
}

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，让我们运行应用程序。如果应用程序一切正常，它将打印以下消息。

Updated Record with ID = 1

您可以通过查询数据库来检查存储的byte[]。