Spring JDBC ResultSetExtractor介面範例


org.springframework.jdbc.core.ResultSetExtractor介面是JdbcTemplate的查詢方法使用的回撥介面。此介面的實現執行從ResultSet提取結果的實際工作,不需要擔心例外處理,它呼叫JdbcTemplate捕獲並處理SQLExceptions。 該介面主要用於JDBC框架本身。 RowMapper通常是ResultSet處理的簡單選擇查詢,每行對映一個結果物件,而不是整個ResultSet的一個結果物件。

介面的宣告

以下是org.springframework.jdbc.core.ResultSetExtractor介面的宣告 -

public interface ResultSetExtractor

用法

步驟1 - 使用組態的資料源建立一個JdbcTemplate物件。
步驟2 - 在使用ResultSetExtractor解析結果集時,使用JdbcTemplate物件方法進行資料庫操作。

範例

以下範例將演示如何使用JdbcTemplate類和ResultSetExtractor介面進行讀取查詢。這裡我們將從student表中讀取記錄。

語法

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;
}

在上面範例(語法)程式碼中 -

  • SQL - 選擇查詢語句來來讀取學生記錄資訊。
  • jdbcTemplateObject - StudentJDBCTemplate物件從資料庫中讀取Student物件。
  • ResultSetExtractor - ResultSetExtractor物件用來解析resultset物件。

範例專案

要了解上述與Spring JDBC相關的概念,下面我們編寫一個select查詢語句的範例。開啟Eclipse IDE,並按照以下步驟建立一個Spring應用程式,這裡建立一個名稱為:ResultSetExtractor 的專案。

步驟說明

  1. 參考第一個Spring JDBC專案來建立一個Maven專案 - /20/235/8754.html
  2. 更新bean組態並執行應用程式。

完整的專案結構如下所示 -

以下是Maven組態檔案:pom.xml的程式碼內容:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.yiibai</groupId>
    <artifactId>ResultSetExtractor</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>ResultSetExtractor</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.40</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>4.1.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.1.4.RELEASE</version>
        </dependency>
    </dependencies>
</project>

以下是資料存取物件介面檔案:StudentDAO.java的內容:

package com.yiibai;

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();
    public Student getStudent(Integer id);
    public void create(String name, Integer age);

}

以下是檔案:Student.java的程式碼內容:

package com.yiibai;

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;
    }
}

以下是檔案:StudentMapper.java的程式碼內容:

package com.yiibai;

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

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;
   }
}

實現類StudentJDBCTemplate.java實現了定義的DAO介面 - StudentDAO.java,以下是檔案:StudentJDBCTemplate.java的程式碼內容:

package com.yiibai;

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

import org.springframework.dao.DataAccessException;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.PreparedStatementSetter;
import org.springframework.jdbc.core.ResultSetExtractor;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

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;
    }

    public void create(String name, Integer age) {
        // TODO Auto-generated method stub
        String insertQuery = "insert into student (name, age) values (?, ?)";

        jdbcTemplateObject.update(insertQuery, name, age);
        System.out.println("Created Record Name = " + name + " Age = " + age);
        return;
    }

    public Student getStudent(final Integer id) {
        final String SQL = "select * from Student where id = ? ";
        List<Student> students = jdbcTemplateObject.query(SQL, new PreparedStatementSetter() {
            public void setValues(PreparedStatement preparedStatement) throws SQLException {
                preparedStatement.setInt(1, id);
            }
        }, new StudentMapper());
        return students.get(0);
    }
}

以下是檔案:MainApp.java的程式碼內容:

package com.yiibai;

import java.util.ArrayList;
import java.util.List;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.yiibai.StudentJDBCTemplate;

public class MainApp {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("application-beans.xml");

        StudentJDBCTemplate studentJDBCTemplate = (StudentJDBCTemplate) context.getBean("studentJDBCTemplate");

        System.out.println("------Records Creation--------");
        studentJDBCTemplate.create("Maxsu", 21);
        studentJDBCTemplate.create("Curry", 22);
        studentJDBCTemplate.create("Suzend", 23);

        List<Student> students = studentJDBCTemplate.listStudents();

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

以下是檔案:application-beans.xml的程式碼內容:

<?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.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=utf8&useSSL=true" />
        <property name="username" value="root" />
        <property name="password" value="123456" />
    </bean>

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

</beans>

注意: application-beans.xml 檔案的位置是:{workspace}/fistapp/src/main/java 目錄,如果放置錯了,程式可能會因為找不到此組態檔案而出錯。

完成建立原始碼和bean和資料庫連線資訊的檔案組態後,執行應用程式。這裡先簡單說明一下執行的步驟,在專案名稱(ResultSetExtractor)上點選右鍵,在彈出的選單中選擇:【Run As】-> 【Maven test】

在執行測試成功後,應該會輸出類似以下內容(含有 BUILD SUCCESS 的資訊) 。
接下來,點選類檔案:MainApp.java 選擇【Run As】->【Java Application】,如果應用程式一切正常,這將列印以下結果:

------Records Creation--------
Created Record Name = Maxsu Age = 21
Created Record Name = Curry Age = 22
Created Record Name = Suzend Age = 23
ID : 1, Age : 21
ID : 2, Age : 22
ID : 3, Age : 23