Dbutils 简明教程

MapListHandler Class

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

The org.apache.commons.dbutils.MapListHandler is the implementation of ResultSetHandler interface and is responsible to convert the ResultSet rows into list of Maps. This class is thread safe.

Class Declaration

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

Following is the declaration for org.apache.commons.dbutils.MapListHandler class −

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

Usage

  1. Step 1 − Create a connection object.

  2. Step 2 − Get implementation of ResultSetHandler as MapListHandler object.

  3. Step 3 − Pass resultSetHandler to QueryRunner object, and make database operations.

Example

以下示例演示如何使用MapListHandler类读取记录列表。我们将把Employees表中的可用记录作为Map列表进行读取。

Following example will demonstrate how to read a list of records using MapListHandler class. We’ll read available records in Employees Table as list of maps.

Syntax

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

其中，

Where,

  1. resultHandler − MapListHandler object to map result sets to list of maps.

  2. queryRunner − QueryRunner object to read employee object from database.

为了理解上述与 DBUtils 相关的概念，让我们编写一个将运行读取查询的示例。为了编写我们的示例，让我们创建一个示例应用程序。

To understand the above-mentioned concepts related to DBUtils, let us write an example which will run a read query. To write our example, let us create a sample application.

Step

Description

1

Update the file MainApp.java created under chapter DBUtils - First Application.

2

Compile and run the application as explained below.

以下是 Employee.java 的内容。

Following is the content of the Employee.java.

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。

Following is the content of the MainApp.java file.

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 driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
   static final String DB_URL = "jdbc:mysql://localhost:3306/emp";

   //  Database credentials
   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();

      //Step 1: Register JDBC driver
      DbUtils.loadDriver(JDBC_DRIVER);

      //Step 2: Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER, PASS);

      try {
         List<Map<String, Object>> result = queryRunner.query(
            conn, "SELECT * FROM employees", new MapListHandler());
         System.out.println(result);
      } finally {
         DbUtils.close(conn);
      }
   }
}

一旦你创建好源文件，让我们运行应用程序。如果你的应用程序没有问题，它将打印以下消息。

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

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=Mittal}]