📅  最后修改于: 2020-11-18 08:10:26             🧑  作者: Mango
org.apache.commons.dbutils.BeanHandler是ResultSetHandler接口的实现,负责将第一个ResultSet行转换为JavaBean。此类是线程安全的。
以下是org.apache.commons.dbutils.BeanHandler类的声明-
public class BeanHandler
extends Object implements ResultSetHandler
步骤1-创建一个连接对象。
第2步-获取ResultSetHandler的实现作为BeanHandler对象。
步骤3-将resultSetHandler传递给QueryRunner对象,并进行数据库操作。
下面的示例将演示如何使用BeanHandler类读取记录。我们将在Employees Table中读取一条可用记录,并将其映射到Employee bean。
Employee emp = queryRunner.query(conn, "SELECT * FROM employees WHERE first=?", resultHandler, "Sumit");
哪里,
resultHandler -BeanHandler对象将结果集映射到Employee对象。
queryRunner -QueryRunner对象,用于从数据库读取员工对象。
为了理解与DBUtils有关的上述概念,让我们编写一个示例,该示例将运行读取查询。为了编写示例,让我们创建一个示例应用程序。
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。
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 org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;
import org.apache.commons.dbutils.handlers.BeanHandler;
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);
//Step 3: Create a ResultSet Handler to handle Employee Beans
ResultSetHandler resultHandler
= new BeanHandler(Employee.class);
try {
Employee emp = queryRunner.query(conn, "SELECT * FROM employees WHERE first=?",
resultHandler, "Sumit");
//Display values
System.out.print("ID: " + emp.getId());
System.out.print(", Age: " + emp.getAge());
System.out.print(", First: " + emp.getFirst());
System.out.println(", Last: " + emp.getLast());
} finally {
DbUtils.close(conn);
}
}
}
创建完源文件后,让我们运行该应用程序。如果您的应用程序一切正常,它将打印以下消息。
ID: 103, Age: 28, First: Sumit, Last: Mittal