无涯教程-DBUtils - MapListHandler接口 org.apache.commons.dbutils.M

org.apache.commons.dbutils.MapListHandler 是ResultSetHandler接口的实现，负责将ResultSet行转换为Maps列表，此类是线程安全的。

MapListHandler - 声明

以下是org.apache.commons.dbutils.MapListHandler类的声明-

public class MapListHandler
   extends AbstractListHandler<Map<String,Object>>

MapListHandler - 使用

步骤1 -创建一个连接对象。
步骤2 -将ResultSetHandler的实现作为MapListHandler对象获得。
步骤3 -将resultSetHandler传递给QueryRunner对象，并进行数据库操作。

MapListHandler - 示例

下面的示例将演示如何使用MapListHandler类读取记录列表。无涯教程将读取雇员表中的可用记录作为Map列表。

List<Map<String, Object>> result=queryRunner.query(conn, "SELECT * FROM employees", new MapListHandler());

resultHandler - 将输出集映射到Map列表的MapListHandler对象。
queryRunner - QueryRunner对象，用于从数据库读取员工对象。

以下是 Employee.java 的内容。

public class Employee {
   private int id;
   private int age;
   private String first;
   private String last;
   public int getId() {
      return id;
   }
   public void setId(int id) {
      this.id = id;
   }
   public int getAge() {
      return age;
   }
   public void setAge(int age) {
      this.age = age;
   }
   public String getFirst() {
      return first;
   }
   public void setFirst(String first) {
      this.first = first;
   }
   public String getLast() {
      return last;
   }
   public void setLast(String last) {
      this.last = last;
   }
}

以下是 MainApp.java 文件的内容。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;
import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.MapListHandler;
public class MainApp {
//JDBC 驱动程序名称和数据库 URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";

static final String DB_URL = "jdbc:mysql://localhost:3306/emp";
//连接数据库凭据
static final String USER = "root";
static final String PASS = "admin";
public static void main(String[] args) throws SQLException {
Connection conn = null;
QueryRunner queryRunner = new QueryRunner();
  </span><span class="com">//第一步：注册JDBC驱动</span><span class="pln">
  </span><span class="typ">DbUtils</span><span class="pun">.</span><span class="pln">loadDriver</span><span class="pun">(</span><span class="pln">JDBC_DRIVER</span><span class="pun">);</span><span class="pln">

  </span><span class="com">//第二步：打开连接</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Connecting to database..."</span><span class="pun">);</span><span class="pln">
  conn </span><span class="pun">=</span><span class="pln"> </span><span class="typ">DriverManager</span><span class="pun">.</span><span class="pln">getConnection</span><span class="pun">(</span><span class="pln">DB_URL</span><span class="pun">,</span><span class="pln"> USER</span><span class="pun">,</span><span class="pln"> PASS</span><span class="pun">);</span><span class="pln">        

  </span><span class="kwd">try</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">List</span><span class="pun">&lt;</span><span class="typ">Map</span><span class="pun">&lt;</span><span class="typ">String</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Object</span><span class="pun">&gt;&gt;</span><span class="pln"> result 
        </span><span class="pun">=</span><span class="pln"> queryRunner</span><span class="pun">.</span><span class="pln">query</span><span class="pun">(</span><span class="pln">conn</span><span class="pun">,</span><span class="pln"> </span><span class="str">"SELECT * FROM employees"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">MapListHandler</span><span class="pun">());</span><span class="pln">      
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">result</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln"> </span><span class="kwd">finally</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">DbUtils</span><span class="pun">.</span><span class="pln">close</span><span class="pun">(</span><span class="pln">conn</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">        

}
}

创建完源文件后，让无涯教程运行该应用程序。如果您的应用程序一切正常，它将打印以下消息。

Connecting to database...
[{id=100, age=18, first=Zara, last=Ali}, 
{id=101, age=25, first=Mahnaz, last=Fatma}, 
{id=102, age=30, first=Zaid, last=Khan}, 
{id=103, age=33, first=Sumit, last=Learnfk}]

无涯教程-DBUtils - MapListHandler接口

MapListHandler - 声明

MapListHandler - 使用

MapListHandler - 示例

参考链接