H2数据库-通话

H2数据库是一款轻量级的Java数据库，具有高性能、开源免费、支持多种模式（嵌入式/服务器）、支持多种数据库标准（JDBC/ODBC/OLE）等优点。在通话应用中，H2数据库可以被用于存储通话记录、联系人信息等数据。本文将介绍如何在通话应用中使用H2数据库。

H2数据库的特点

1. 高性能：H2数据库采用高效的算法和数据结构，具有很高的性能。
2. 开源免费：H2数据库采用Mozilla Public License 2.0协议，免费开源。
3. 支持多种模式：H2数据库可以作为嵌入式数据库，也可以作为服务器数据库。
4. 支持多种数据库标准：H2数据库支持JDBC、ODBC和OLE等标准。
5. 易于使用：H2数据库提供了简单易用的API接口。
6. 支持内存数据库：H2数据库可以在内存中运行，不需要安装并配置数据库。

H2数据库的使用

引入依赖

在Maven项目中引入以下依赖：

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>1.4.200</version>
</dependency>

在Gradle项目中引入以下依赖：

compile group: 'com.h2database', name: 'h2', version: '1.4.200'

连接数据库

使用以下代码连接数据库：

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

public class DatabaseConnector {

    private static final String DATABASE_URL = "jdbc:h2:~/test";
    private static final String DATABASE_USER = "sa";
    private static final String DATABASE_PASSWORD = "";

    public static Connection connect() throws SQLException {
        return DriverManager.getConnection(DATABASE_URL, DATABASE_USER, DATABASE_PASSWORD);
    }
}

其中，DATABASE_URL为H2数据库的URL，~/test表示创建一个名为test的数据库，用户为sa，没有密码。需要注意的是，数据 URL 的前缀必须是 jdbc:h2:，或者是 jdbc:h2:mem:。如果是后者，则表示在内存中创建一个数据库。

创建表格

使用以下代码创建表格：

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;

public class TableCreator {

    public static void createTables(Connection connection) throws SQLException {
        Statement statement = connection.createStatement();
        String sql = "CREATE TABLE IF NOT EXISTS CALLS (" 
                    + "id INT PRIMARY KEY AUTO_INCREMENT," 
                    + "caller_number VARCHAR(20),"
                    + "callee_number VARCHAR(20),"
                    + "start_time TIMESTAMP,"
                    + "end_time TIMESTAMP,"
                    + "duration INT"
                    + ");";
        statement.executeUpdate(sql);
    }
}

其中，sql语句定义了一个名为CALLS、包含id、caller_number、callee_number、start_time、end_time、duration六个字段的表格。id字段为主键，自增，caller_number、callee_number为打电话者和接电话者的号码，start_time、end_time为通话开始和结束时间，duration为通话时长。

添加数据

使用以下代码添加数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class DataInserter {

    public static void insertData(Connection connection, String callerNumber, String calleeNumber, LocalDateTime startTime, LocalDateTime endTime, int duration) throws SQLException {
        String sql = "INSERT INTO CALLS (caller_number, callee_number, start_time, end_time, duration) VALUES (?, ?, ?, ?, ?);";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setString(1, callerNumber);
        statement.setString(2, calleeNumber);
        statement.setTimestamp(3, Timestamp.valueOf(startTime));
        statement.setTimestamp(4, Timestamp.valueOf(endTime));
        statement.setInt(5, duration);
        statement.executeUpdate();
    }
}

其中，callerNumber、calleeNumber为字符串类型的打电话者和接电话者号码，startTime、endTime为时间类型的通话开始和结束时间，duration为整型的通话时长。

查询数据

使用以下代码查询数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class DataSelecter {

    public static List<Call> selectAllData(Connection connection) throws SQLException {
        String sql = "SELECT * FROM CALLS;";
        PreparedStatement statement = connection.prepareStatement(sql);
        ResultSet resultSet = statement.executeQuery();
        List<Call> list = new ArrayList<>();
        while (resultSet.next()) {
            int id = resultSet.getInt("id");
            String callerNumber = resultSet.getString("caller_number");
            String calleeNumber = resultSet.getString("callee_number");
            LocalDateTime startTime = resultSet.getTimestamp("start_time").toLocalDateTime();
            LocalDateTime endTime = resultSet.getTimestamp("end_time").toLocalDateTime();
            int duration = resultSet.getInt("duration");
            Call call = new Call(id, callerNumber, calleeNumber, startTime, endTime, duration);
            list.add(call);
        }
        return list;
    }

    public static Call selectData(Connection connection, int id) throws SQLException {
        String sql = "SELECT * FROM CALLS WHERE id = ?;";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1, id);
        ResultSet resultSet = statement.executeQuery();
        if (resultSet.next()) {
            String callerNumber = resultSet.getString("caller_number");
            String calleeNumber = resultSet.getString("callee_number");
            LocalDateTime startTime = resultSet.getTimestamp("start_time").toLocalDateTime();
            LocalDateTime endTime = resultSet.getTimestamp("end_time").toLocalDateTime();
            int duration = resultSet.getInt("duration");
            return new Call(id, callerNumber, calleeNumber, startTime, endTime, duration);
        } else {
            return null;
        }
    }
}

其中，selectAllData方法用于查询所有通话记录，selectData方法用于查询特定id的通话记录。查询结果以Call的形式封装。

总结

通过本文介绍，读者应该掌握了在通话应用中如何使用H2数据库存储数据的方法。代码片段如下：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Timestamp;
import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;

public class H2Example {

    private static final String DATABASE_URL = "jdbc:h2:~/test";
    private static final String DATABASE_USER = "sa";
    private static final String DATABASE_PASSWORD = "";

    public static Connection connect() throws SQLException {
        return DriverManager.getConnection(DATABASE_URL, DATABASE_USER, DATABASE_PASSWORD);
    }

    public static void createTables(Connection connection) throws SQLException {
        Statement statement = connection.createStatement();
        String sql = "CREATE TABLE IF NOT EXISTS CALLS (" 
                    + "id INT PRIMARY KEY AUTO_INCREMENT," 
                    + "caller_number VARCHAR(20),"
                    + "callee_number VARCHAR(20),"
                    + "start_time TIMESTAMP,"
                    + "end_time TIMESTAMP,"
                    + "duration INT"
                    + ");";
        statement.executeUpdate(sql);
    }

    public static void insertData(Connection connection, String callerNumber, String calleeNumber, LocalDateTime startTime, LocalDateTime endTime, int duration) throws SQLException {
        String sql = "INSERT INTO CALLS (caller_number, callee_number, start_time, end_time, duration) VALUES (?, ?, ?, ?, ?);";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setString(1, callerNumber);
        statement.setString(2, calleeNumber);
        statement.setTimestamp(3, Timestamp.valueOf(startTime));
        statement.setTimestamp(4, Timestamp.valueOf(endTime));
        statement.setInt(5, duration);
        statement.executeUpdate();
    }

    public static List<Call> selectAllData(Connection connection) throws SQLException {
        String sql = "SELECT * FROM CALLS;";
        PreparedStatement statement = connection.prepareStatement(sql);
        ResultSet resultSet = statement.executeQuery();
        List<Call> list = new ArrayList<>();
        while (resultSet.next()) {
            int id = resultSet.getInt("id");
            String callerNumber = resultSet.getString("caller_number");
            String calleeNumber = resultSet.getString("callee_number");
            LocalDateTime startTime = resultSet.getTimestamp("start_time").toLocalDateTime();
            LocalDateTime endTime = resultSet.getTimestamp("end_time").toLocalDateTime();
            int duration = resultSet.getInt("duration");
            Call call = new Call(id, callerNumber, calleeNumber, startTime, endTime, duration);
            list.add(call);
        }
        return list;
    }

    public static Call selectData(Connection connection, int id) throws SQLException {
        String sql = "SELECT * FROM CALLS WHERE id = ?;";
        PreparedStatement statement = connection.prepareStatement(sql);
        statement.setInt(1, id);
        ResultSet resultSet = statement.executeQuery();
        if (resultSet.next()) {
            String callerNumber = resultSet.getString("caller_number");
            String calleeNumber = resultSet.getString("callee_number");
            LocalDateTime startTime = resultSet.getTimestamp("start_time").toLocalDateTime();
            LocalDateTime endTime = resultSet.getTimestamp("end_time").toLocalDateTime();
            int duration = resultSet.getInt("duration");
            return new Call(id, callerNumber, calleeNumber, startTime, endTime, duration);
        } else {
            return null;
        }
    }

    public static void main(String[] args) {
        try {
            Connection connection = connect();
            createTables(connection);
            insertData(connection, "123", "456", LocalDateTime.now().minusHours(1), LocalDateTime.now(), 3600);
            List<Call> calls = selectAllData(connection);
            for (Call call : calls) {
                System.out.println(call);
            }
            Call call = selectData(connection, 1);
            System.out.println(call);
        } catch (SQLException ex) {
            ex.printStackTrace();
        }
    }

    private static class Call {
        private int id;
        private String callerNumber;
        private String calleeNumber;
        private LocalDateTime startTime;
        private LocalDateTime endTime;
        private int duration;

        public Call(int id, String callerNumber, String calleeNumber, LocalDateTime startTime, LocalDateTime endTime, int duration) {
            this.id = id;
            this.callerNumber = callerNumber;
            this.calleeNumber = calleeNumber;
            this.startTime = startTime;
            this.endTime = endTime;
            this.duration = duration;
        }

        @Override
        public String toString() {
            return "Call{" +
                    "id=" + id +
                    ", callerNumber='" + callerNumber + '\'' +
                    ", calleeNumber='" + calleeNumber + '\'' +
                    ", startTime=" + startTime +
                    ", endTime=" + endTime +
                    ", duration=" + duration +
                    '}';
        }
    }
}