Dbutils 简明教程

Custom Row Processor

如果数据库表中的列名和等效 javabean 对象的名称不相似，我们便可以使用自定义 BasicRowProcessor 对象对它们进行映射。请参见以下示例。

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。

Step

Description

1

更新在章节 DBUtils - First Application 下创建的文件 MainApp.java。

2

按以下说明编译并运行应用程序。

以下是 Employee.java 的内容。

public class Employee {
   private int id;
   private int age;
   private String first;
   private String last;
   private String name;
   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;
   }
   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }
}

以下是 EmployeeHandler.java 文件的内容。

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.BeanProcessor;
import org.apache.commons.dbutils.BasicRowProcessor;

public class EmployeeHandler extends BeanHandler<Employee> {

   public EmployeeHandler() {
      super(Employee.class, new BasicRowProcessor(new BeanProcessor(mapColumnsToFields())));
   }

   @Override
   public Employee handle(ResultSet rs) throws SQLException {
      Employee employee = super.handle(rs);
      employee.setName(employee.getFirst() +", " + employee.getLast());
      return employee;
   }

   public static Map<String, String> mapColumnsToFields() {
      Map<String, String> columnsToFieldsMap = new HashMap<>();
      columnsToFieldsMap.put("ID", "id");
      columnsToFieldsMap.put("AGE", "age");
      return columnsToFieldsMap;
   }
}

以下是 MainApp.java 文件的内容。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;

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();
      DbUtils.loadDriver(JDBC_DRIVER);
      conn = DriverManager.getConnection(DB_URL, USER, PASS);
      EmployeeHandler employeeHandler = new EmployeeHandler();

      try {
         Employee emp = queryRunner.query(conn,
           "SELECT * FROM employees WHERE first=?", employeeHandler, "Sumit");

         //Display values
         System.out.print("ID: " + emp.getId());
         System.out.print(", Age: " + emp.getAge());
         System.out.print(", Name: " + emp.getName());
      } 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。

ID: 103, Age: 28, Name: Sumit, Mittal