Java Mysql 简明教程

Java & MySQL - Sample Code

本章提供了一个如何创建一个基于 Java 的简单应用程序来访问 MySQL 数据库的示例。这将向您展示如何打开数据库连接、执行一个 SQL 查询以及显示结果。

This chapter provides an example of how to create a simple java based application to access MySQL database. This will show you how to open a database connection, execute a SQL query, and display the results.

本模板示例中提到的所有步骤都将在本教程的后续章节中进行解释。

All the steps mentioned in this template example, would be explained in subsequent chapters of this tutorial.

Creating JDBC Application

构建一个 JDBC 应用程序涉及以下六个步骤 -

There are following six steps involved in building a JDBC application −

Import the packages: Requires that you include the packages containing the JDBC classes needed for database programming. Most often, using import java.sql.* will suffice.
Open a connection: Requires using the DriverManager.getConnection() method to create a Connection object, which represents a physical connection with the database.
Execute a query: Requires using an object of type Statement for building and submitting an SQL statement to the database.
Extract data from result set − Requires that you use the appropriate ResultSet.getXXX() method to retrieve the data from the result set.
Clean up the environment − Requires explicitly closing all database resources versus relying on the JVM’s garbage collection.

Sample Code

此示例可以充当一种 template ，以便在未来需要创建自己 JDBC 应用时使用。

This sample example can serve as a template when you need to create your own JDBC application in the future.

此示例代码是基于前一章节中完成的环境与数据库设置编写的。

This sample code has been written based on the environment and database setup done in the previous chapter.

将以下示例复制并粘贴到 TestApplication.java 中，如下进行编译和运行：

Copy and paste the following example in TestApplication.java, compile and run as follows −

import java.sql.*;

public class TestApplication {
   static final String DB_URL = "jdbc:mysql://localhost/TUTORIALSPOINT";
   static final String USER = "guest";
   static final String PASS = "guest123";
   static final String QUERY = "SELECT id, first, last, age FROM Employees";

   public static void main(String[] args) {
      // Open a connection
      try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS);
         Statement stmt = conn.createStatement();
         ResultSet rs = stmt.executeQuery(QUERY);) {
         // Extract data from result set
         while (rs.next()) {
            // Retrieve by column name
            System.out.print("ID: " + rs.getInt("id"));
            System.out.print(", Age: " + rs.getInt("age"));
            System.out.print(", First: " + rs.getString("first"));
            System.out.println(", Last: " + rs.getString("last"));
         }
      } catch (SQLException e) {
         e.printStackTrace();
      }
   }
}

现在让我们如下编译上述示例：

Now let us compile the above example as follows −

C:\>javac TestApplication.java
C:\>

运行 TestApplication 时，它会生成以下结果：

When you run TestApplication, it produces the following result −

C:\>java TestApplication
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: 28, First: Sumit, Last: Mittal
C:\>