2024-09-09

以下是一个简单的Spring Boot + MyBatis-Plus + PostgreSQL的CRUD实现示例:

  1. 首先,在pom.xml中添加依赖:



<dependencies>
    <!-- Spring Boot Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
 
    <!-- MyBatis-Plus Starter -->
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.x.x</version>
    </dependency>
 
    <!-- PostgreSQL Starter -->
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jdbc</artifactId>
    </dependency>
    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <scope>runtime</scope>
    </dependency>
</dependencies>
  1. 配置application.propertiesapplication.yml



spring.datasource.url=jdbc:postgresql://localhost:5432/your_database
spring.datasource.username=your_username
spring.datasource.password=your_password
spring.datasource.driver-class-name=org.postgresql.Driver
  1. 创建一个实体类对应数据库表:



import com.baomidou.mybatisplus.annotation.TableName;
 
@TableName("user")
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
 
    // 省略getter和setter方法
}
  1. 创建一个Mapper接口:



import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.apache.ibatis.annotations.Mapper;
 
@Mapper
public interface UserMapper extends BaseMapper<User> {
    // MyBatis-Plus会自动处理CRUD操作
}
  1. 在Spring Boot启动类中添加@MapperScan注解:



import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
 
@SpringBootApplication
@MapperScan("com.yourpackage.mapper")
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}
  1. 使用Mapper进行CRUD操作:



import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
@Service
public class UserService {
 
    @Autowired
    private UserMapper userMapper;
 
    public boolean saveUser(User user) {
        return userMapper.insert(user) > 0;
    }
 
    public User getUser(Long id) {
        return userMapper.selectB
2024-09-09



import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger';
 
async function bootstrap() {
  const app = await NestFactory.create(AppModule);
 
  // 配置Swagger
  const config = new DocumentBuilder()
    .setTitle('网盘系统API')
    .setDescription('网盘系统的后端API接口文档')
    .setVersion('1.0')
    .addTag('网盘系统')
    .build();
  const document = SwaggerModule.createDocument(app, config);
  SwaggerModule.setup('api', app, document);
 
  // 启动服务
  await app.listen(3000);
}
 
bootstrap();

这段代码展示了如何在Nestjs项目中集成Swagger来自动生成API文档,并且设置了API的基本信息,如标题、描述、版本和标签。最后,它启动了Nestjs应用并监听3000端口。这是一个简洁而完整的配置示例,可以作为开发者在自己的项目中集成Swagger的参考。

2024-09-09

在PostgreSQL中,你可以使用以下SQL查询来统计给定时间范围内的15分钟粒度、小时粒度、天粒度、周粒度和月粒度的数据。这些查询假设你有一个表events,它有一个timestamp类型的字段event_time




-- 设置时间范围
SET @start_time = '2023-01-01 00:00:00';
SET @end_time = '2023-01-31 23:59:59';
 
-- 15分钟粒度统计
SELECT
  date_trunc('hour', event_time) as hour,
  date_trunc('hour', event_time) + INTERVAL '15 minutes' as quarter_hour,
  COUNT(*) as event_count
FROM
  events
WHERE
  event_time >= @start_time
  AND event_time < @end_time
GROUP BY
  hour,
  quarter_hour
ORDER BY
  hour,
  quarter_hour;
 
-- 小时粒度统计
SELECT
  date_trunc('day', event_time) as day,
  date_trunc('hour', event_time) as hour,
  COUNT(*) as event_count
FROM
  events
WHERE
  event_time >= @start_time
  AND event_time < @end_time
GROUP BY
  day,
  hour
ORDER BY
  day,
  hour;
 
-- 天粒度统计
SELECT
  date_trunc('week', event_time) as week,
  date_trunc('day', event_time) as day,
  COUNT(*) as event_count
FROM
  events
WHERE
  event_time >= @start_time
  AND event_time < @end_time
GROUP BY
  week,
  day
ORDER BY
  week,
  day;
 
-- 周粒度统计
SELECT
  date_trunc('month', event_time) as month,
  date_trunc('week', event_time) as week,
  COUNT(*) as event_count
FROM
  events
WHERE
  event_time >= @start_time
  AND event_time < @end_time
GROUP BY
  month,
  week
ORDER BY
  month,
  week;
 
-- 月粒度统计
SELECT
  date_trunc('year', event_time) as year,
  date_trunc('month', event_time) as month,
  COUNT(*) as event_count
FROM
  events
WHERE
  event_time >= @start_time
  AND event_time < @end_time
GROUP BY
  year,
  month
ORDER BY
  year,
  month;

请确保将@start_time@end_time设置为你想要分析的时间范围,并将events替换为你的实际表名以及event_time替换为你的时间戳字段。这些查询使用了date_trunc函数来获取时间的年、月、日、小时、周的起始时间,并使用COUNT聚合函数来统计每个时间段内的事件数量。

2024-09-09

在Oracle Real Application Clusters (RAC)环境中,每个节点可能会运行多个代理(agents),这些代理负责管理不同的资源(resource)。为了更好地理解这些agents和resources之间的关系,以下是一个简化的代码示例,用于创建和管理这些资源。




-- 创建一个新的资源,例如一个Oracle实例
BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_CONSUMER_GROUP(
    consumer_group => 'rac_inst_cg',
    comments => 'Consumer group for RAC instances'
  );
 
  DBMS_RESOURCE_MANAGER.CREATE_PLAN(
    plan => 'rac_plan',
    comment => 'Resource plan for RAC',
    active_for_n_periods => 1,
    period_length => 1,
    period_type => DBMS_RESOURCE_MANAGER.MONTHLY
  );
 
  DBMS_RESOURCE_MANAGER.CREATE_PIN(
    pin => 'rac_inst_pin',
    consumer_group => 'rac_inst_cg',
    plan => 'rac_plan',
    quantity => 100,
    override => FALSE
  );
 
  -- 注册资源消费者
  DBMS_RESOURCE_MANAGER.CREATE_CONSUMER(
    consumer_name => 'rac_inst_consumer',
    consumer_group => 'rac_inst_cg',
    queueing_clause => 'BY (inst_id, resource_name)',
    comments => 'Consumer for RAC instances'
  );
 
  -- 注册代理和资源
  DBMS_RESOURCE_MANAGER.REGISTER_RESOURCE_TYPE(
    resource_type => 'rac_inst_resource',
    consumer_group => 'rac_inst_cg',
    queueing_clause => 'BY (inst_id, resource_name)',
    max_utilization => 100,
    initial_utilization => 0,
    instance_aware => TRUE
  );
 
  -- 为每个节点实例化代理
  FOR i IN 1..n LOOP
    DBMS_RESOURCE_MANAGER.CREATE_AGENT(
      agent_name => 'rac_inst_agent_' || i,
      resource_type => 'rac_inst_resource',
      resource_consumer => 'rac_inst_consumer',
      resource_plan => 'rac_plan',
      profile => NULL,
      initial_allocation => 0,
      max_allocation => 100,
      instance_id => i
    );
  END LOOP;
END;
/

这段代码首先创建了一个消费者组、资源计划和PIN,然后定义了一个资源类型,并为每个节点实例化了一个代理。这样,每个节点的资源使用情况就可以被监控和管理。这个例子提供了一个清晰的视图,展示了agents和resources是如何在RAC环境中配合工作的。

2024-09-09

Tomcat session复制和session共享通常涉及以下几种方法:

  1. 使用Tomcat自带的session复制功能:在<Cluster>标签中配置相应的<Channel><Valve>,这通常需要配置jgroupsUDP协议。
  2. 使用第三方集群解决方案:比如Apache JEESession Cluster (JSC)或者ShareSession。
  3. 自定义HttpSessionListener :实现HttpSessionListener接口,在session创建和销毁时进行复制或共享。

以下是一个简单的自定义HttpSessionListener的例子,用于演示如何在session创建时记录一条消息:




import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
 
public class CustomSessionListener implements HttpSessionListener {
 
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        // 当session被创建时,可以在这里进行复制或者共享的逻辑
        System.out.println("Session created with id: " + se.getSession().getId());
    }
 
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        // 当session销毁时,可以在这里进行复制或者共享的逻辑
        System.out.println("Session destroyed with id: " + se.getSession().getId());
    }
}

web.xml中注册这个监听器:




<listener>
    <listener-class>CustomSessionListener</listener-class>
</listener>

这个例子只是展示了如何通过实现HttpSessionListener接口来监听session的创建和销毁。在实际的复制和共享场景中,复制逻辑会更加复杂,可能需要序列化、网络传输以及反序列化等步骤。

2024-09-09

在CentOS 7上安装PostgreSQL和PostGIS的步骤如下:

  1. 添加PostgreSQL的官方Yum仓库:



sudo yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
  1. 清除缓存:



sudo yum clean all
  1. 安装PostgreSQL和PostGIS:



sudo yum install -y postgresql12-server postgresql12-contrib postgis24_12
  1. 初始化数据库并启动服务:



sudo /usr/pgsql-12/bin/postgresql-12-setup initdb
sudo systemctl enable postgresql-12
sudo systemctl start postgresql-12
  1. 确认PostGIS安装成功:



psql -U postgres
postgres=# CREATE EXTENSION postgis;
postgres=# \q

以上步骤会安装PostgreSQL 12和PostGIS 2.4,请根据需要选择合适的PostgreSQL和PostGIS版本。

2024-09-09

在PostgreSQL中,可以使用INTERVAL类型进行时间的加减操作。以下是一些示例:




-- 当前时间加5小时
SELECT NOW() + INTERVAL '5 hour';
 
-- 当前时间减5分钟
SELECT NOW() - INTERVAL '5 minute';
 
-- 特定日期加3天
SELECT '2023-01-01'::date + INTERVAL '3 day';
 
-- 特定时间加10小时30分钟
SELECT '10:30'::time + INTERVAL '10 hour 30 minute';
 
-- 从当前时间减去一个时间间隔
SELECT NOW() - INTERVAL '1 week 2 days 3 hours';
 
-- 时间加上一个数字(天数)
SELECT '2023-01-01'::date + 30;
 
-- 时间减去一个数字(天数)
SELECT '2023-01-01'::date - 15;

这些例子展示了如何在PostgreSQL中对时间进行加减操作。可以使用INTERVAL类型或直接用数字和datetime类型结合运算符进行简单的时间加减。

2024-09-06

在Oracle数据库中,sqlnet.ora 文件用于配置网络,定义客户端如何解析数据库连接字符串。transnames.ora 文件是在Oracle 8i及更早版本中使用的文件,用于定义数据库别名,但在Oracle 9i及更高版本中,这个文件已经被tnsnames.ora文件取代。

对于Oracle 9i及更高版本,数据库标识符通常是通过tnsnames.ora进行配置的,而不是transnames.ora。在tnsnames.ora文件中,你可以定义网络服务名(或称为别名),它包含了连接到数据库所需的详细信息,如主机名、端口号和SID或服务名。

以下是一个tnsnames.ora文件的示例配置:




MYDB =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = mydbhost.example.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SID = orcl)
    )
  )

在这个例子中,MYDB 是网络服务名,mydbhost.example.com 是数据库服务器的主机名,1521 是端口号,orcl 是数据库的SID。

确保sqlnet.ora文件中的NAMES.DIRECTORY_PATH参数包含tnsnames,如下所示:




NAMES.DIRECTORY_PATH= (TNSNAMES, EZCONNECT)

这样,Oracle客户端软件就会首先查找tnsnames.ora文件来解析网络服务名。

2024-09-06

在Linux上安装PostgreSQL可以通过包管理器或者从源代码编译。以下是使用Ubuntu或Debian系统的APT包管理器安装PostgreSQL的步骤:

  1. 更新包索引:



sudo apt update
  1. 安装PostgreSQL:



sudo apt install postgresql postgresql-contrib
  1. 启动PostgreSQL服务:



sudo service postgresql start
  1. 确认PostgreSQL正在运行:



sudo service postgresql status
  1. 切换到PostgreSQL用户(默认为postgres):



sudo -i -u postgres
  1. 创建一个新的角色(可选):



createuser --interactive
  1. 创建一个新的数据库(可选):



createdb <your_database_name>
  1. 登录到PostgreSQL命令行界面:



psql

以上步骤安装了PostgreSQL,启动了服务,并允许你通过交互式命令创建用户和数据库。

2024-09-06



/*
 * PostmasterMain -- Initialize process environment, fork child processes, etc.
 *
 * argc/argv are the usual main() arguments.  Note these are NOT necessarily
 * passed directly by the user's shell, they might be from a wrapper script
 * created by the makefiles.  Use the originalArgs variable if you need to
 * find out what the shell command was.
 */
int
PostmasterMain(int argc, char *argv[])
{
    // ... 省略前面的代码 ...
 
    /*
     * Main loop for postmaster
     */
    for (;;)
    {
        int            delay;
 
        if (IsUnderPostmaster)
            SendPostmasterSignal(PMSIGNAL_STATE_CHANGE);
 
        /*
         * Examine the shared memory exit status, if any.  This will cause us
         * to exit if we're supposed to shut down.
         */
        if (Shutdown)
        {
            /*
             * Note: if we are here, the postmaster didn't start up successfully
             * and needs to exit.  But check for a pending signal before we
             * do so.  This might be a SIGQUIT due to a client-side timeout, so
             * be careful not to throw away a real signal intent.
             */
            if (pending_signals)
                sigprocmask(SIG_DISPATCH, NULL, NULL);
 
            /*
             * If we are shutting down, but still have a PGDATA directory,
             * perform a checkpoint to ensure that all WAL segments are marked
             * as saved before we continue to remove data directories and files.
             *
             * Note: If there is a shutdown in progress, Recovery.c will not
             * recognize as a crash, and will not enter recovery when restarting.
             * This means that the checkpoint is only performed when the postmaster
             * is not running, or the database is running without recovery.
             */
            if (FindMyDatabase() >= 0 && !ShutdownWAL())
                elog(WARNING, "WAL checkpoint failed during shutdown");
 
            exit(1);
        }
 
        /*
         * Sleep until something happens.  Note we don't wait for the full
         * delay time, because a signal or SIGQUIT may interrupt the sleep.
         * (Note also that signals interrupt the sleep() call on some
         * platforms but not all.  Therefore, do not rely on this as the
         * sole means of responding to signals in a timely manner.)
         */
        delay = PG_SLEEP_DELAY_MS * 1000;