Java 基础示例

Note

本篇文档所介绍的演示程序的源代码下载地址为：Java CRUD 示例。

配置环境

在开始之前，请确保已经下载并安装了以下软件。

• 完成单机部署 MatrixOne，通过 MySQL 客户端创建数据库。

mysql> create database test;

• 下载安装 lntelliJ IDEA(2022.2.1 or later version)。
• 根据你的系统环境选择 JDK 8+ version 版本进行下载安装。
• MySQL JDBC connector 8.0+ version：推荐下载平台独立版本，并解压下载文件。

Note

我们使用 IDEA 作为一个 IDE 示例来演示这个过程，你可以自由地选择 Eclipse 或其他 IDE 工具实践。

初始化一个新的 Java 项目

启动 IDEA，并创建一个新的 Java 项目，如下所示：

进入菜单 Project Setting > Libraries，导入 mysql-connector-java-8.0.30.jar 文件。

编写 Java 代码连接 MatrixOne

首先，创建一个名为 JDBCUtils 的 Java 类作为连接实用程序。这个类将作为连接 MatrixOne 和执行 SQL 查询的工具。

在 src 目录下，创建一个名为 JDBCUtils.java 的文件，并使用以下代码编辑该文件：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class JDBCUtils {
    private static String jdbcURL = "jdbc:mysql://127.0.0.1:6001/test";
    private static String jdbcUsername = "dump";
    private static String jdbcPassword = "111";
    public static Connection getConnection() {
        Connection connection = null;
        try {
            connection = DriverManager.getConnection(jdbcURL, jdbcUsername, jdbcPassword);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return connection;
    }
    public static void printSQLException(SQLException ex) {
        for (Throwable e : ex) {
            if (e instanceof SQLException) {
                e.printStackTrace(System.err);
                System.err.println("SQLState: " + ((SQLException) e).getSQLState());
                System.err.println("Error Code: " + ((SQLException) e).getErrorCode());
                System.err.println("Message: " + e.getMessage());
                Throwable t = ex.getCause();
                while (t != null) {
                    System.out.println("Cause: " + t);
                    t = t.getCause();
                }
            }
        }
    }
}

其次，我们用 MatrixOne 编写创建、插入、更新和删除操作的示例代码。

我们需要在 src 目录下创建相应的 java 源代码文件：Create.java、Insert.java、Update.java、Select.java，并将下面的代码对应放在这些文件中。

创建（Create.java)

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
public class Create {
    private static final String createTableSQL = "create table student (\r\n" + "  id int primary key,\r\n" +
            "  name varchar(20),\r\n" + "  email varchar(20),\r\n" + "  country varchar(20),\r\n" +
            "  age int\r\n" + "  );";
    public static void main(String[] argv) throws SQLException {
        Create createTable = new Create();
        createTable.createTable();
    }
    public void createTable() throws SQLException {
        System.out.println(createTableSQL);
        // Step 1: Establishing a Connection
        try (Connection connection = JDBCUtils.getConnection();
             // Step 2:Create a statement using connection object
             Statement statement = connection.createStatement();) {
            // Step 3: Execute the query or update query
            statement.execute(createTableSQL);
        } catch (SQLException e) {
            // print SQL exception information
            JDBCUtils.printSQLException(e);
        }
        // Step 4: try-with-resource statement will auto close the connection.
    }
}

执行上述代码会在 test 数据库中创建一个表，然后你可以在 MySQL 客户端中使用如下代码验证是否创建了表。

mysql> show create table student;
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                                                                        |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`id` INT DEFAULT NULL,
`name` VARCHAR(20) DEFAULT NULL,
`email` VARCHAR(20) DEFAULT NULL,
`country` VARCHAR(20) DEFAULT NULL,
`age` INT DEFAULT NULL,
PRIMARY KEY (`id`)
) |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

插入（Insert.java）

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class Insert {
    private static final String INSERT_STUDENT_SQL = "INSERT INTO student" +
            "  (id, name, email, country, age) VALUES " +
            " (?, ?, ?, ?, ?);";
    public static void main(String[] argv) throws SQLException {
        Insert insertTable = new Insert();
        insertTable.insertRecord();
    }
    public void insertRecord() throws SQLException {
        System.out.println(INSERT_STUDENT_SQL);
        // Step 1: Establishing a Connection
        try (Connection connection = JDBCUtils.getConnection();
             // Step 2:Create a statement using connection object
             PreparedStatement preparedStatement = connection.prepareStatement(INSERT_STUDENT_SQL)) {
            preparedStatement.setInt(1, 1);
            preparedStatement.setString(2, "Tony");
            preparedStatement.setString(3, "tony@gmail.com");
            preparedStatement.setString(4, "US");
            preparedStatement.setString(5, "20");
            System.out.println(preparedStatement);
            // Step 3: Execute the query or update query
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // print SQL exception information
            JDBCUtils.printSQLException(e);
        }
        // Step 4: try-with-resource statement will auto close the connection.
    }
}

执行结果：

mysql> select * from student;
+------+------+----------------+---------+------+
| id   | name | email          | country | age  |
+------+------+----------------+---------+------+
|    1 | Tony | tony@gmail.com | US      |   20 |
+------+------+----------------+---------+------+
1 row in set (0.01 sec)

更新（Update.java）

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class Update {
    private static final String UPDATE_STUDENT_SQL = "update student set name = ? where id = ?;";
    public static void main(String[] argv) throws SQLException {
        Update updateTable = new Update();
        updateTable.updateRecord();
    }
    public void updateRecord() throws SQLException {
        System.out.println(UPDATE_STUDENT_SQL);
        // Step 1: Establishing a Connection
        try (Connection connection = JDBCUtils.getConnection();
             // Step 2:Create a statement using connection object
             PreparedStatement preparedStatement = connection.prepareStatement(UPDATE_STUDENT_SQL)) {
            preparedStatement.setString(1, "Ram");
            preparedStatement.setInt(2, 1);
            // Step 3: Execute the query or update query
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // print SQL exception information
            JDBCUtils.printSQLException(e);
        }
        // Step 4: try-with-resource statement will auto close the connection.
    }
}

运行结果：

mysql> select * from student;
+------+------+----------------+---------+------+
| id   | name | email          | country | age  |
+------+------+----------------+---------+------+
|    1 | Ram  | tony@gmail.com | US      |   20 |
+------+------+----------------+---------+------+
1 row in set (0.00 sec)

查询（Select.java）

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class Select {
    private static final String QUERY = "select id,name,email,country,age from student where id =?";
    public static void main(String[] args) {
        // using try-with-resources to avoid closing resources (boiler plate code)
        // Step 1: Establishing a Connection
        try (Connection connection = JDBCUtils.getConnection();
             // Step 2:Create a statement using connection object
             PreparedStatement preparedStatement = connection.prepareStatement(QUERY);) {
            preparedStatement.setInt(1, 1);
            System.out.println(preparedStatement);
            // Step 3: Execute the query or update query
            ResultSet rs = preparedStatement.executeQuery();
            // Step 4: Process the ResultSet object.
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                String email = rs.getString("email");
                String country = rs.getString("country");
                String password = rs.getString("age");
                System.out.println(id + "," + name + "," + email + "," + country + "," + password);
            }
        } catch (SQLException e) {
            JDBCUtils.printSQLException(e);
        }
        // Step 4: try-with-resource statement will auto close the connection.
    }
}

运行结果：