shell复制代码sudo hostnamectl set-hostname example.com

shell复制代码sudo apt-get update
sudo apt-get install postfix -y

shell复制代码sudo ss -lnpt | grep master

shell复制代码sudo apt-get install mailutils

shell复制代码telnet  mx1.qq.com 25

c复制代码/*定义位置PID与速度PID结构体型的全局变量*/
PID pid_location;
PID pid_speed;

/**
  * @brief  PID参数初始化
  *	@note 	无
  * @retval 无
  */
void PID_param_init()
{
	/* 位置相关初始化参数 */
	pid_location.target_val = TOTAL_RESOLUTION*10;				
	pid_location.output_val = 0.0;
	pid_location.err = 0.0;
	pid_location.err_last = 0.0;
	pid_location.integral = 0.0;

	pid_location.Kp = 0.05;
	pid_location.Ki = 0;
	pid_location.Kd = 0;

	/* 速度相关初始化参数 */
	pid_speed.target_val=10.0;				
	pid_speed.output_val=0.0;
	pid_speed.err=0.0;
	pid_speed.err_last=0.0;
	pid_speed.integral=0.0;

	pid_speed.Kp = 80.0;
	pid_speed.Ki = 2.0;
	pid_speed.Kd = 100.0;
}

c复制代码/**
  * @brief  位置PID算法实现
  * @param  actual_val:实际值
  *	@note 	无
  * @retval 通过PID计算后的输出
  */
#define LOC_DEAD_ZONE 60 /*位置环死区*/
#define LOC_INTEGRAL_START_ERR 200 /*积分分离时对应的误差范围*/
#define LOC_INTEGRAL_MAX_VAL 800   /*积分范围限定，防止积分饱和*/
float location_pid_realize(PID *pid, float actual_val)
{
	/*计算目标值与实际值的误差*/
	pid->err = pid->target_val - actual_val;

	/* 设定闭环死区 */
	if((pid->err >= -LOC_DEAD_ZONE) && (pid->err <= LOC_DEAD_ZONE))
	{
		pid->err = 0;
		pid->integral = 0;
		pid->err_last = 0;
	}

	/*积分项，积分分离，偏差较大时去掉积分作用*/
	if(pid->err > -LOC_INTEGRAL_START_ERR && pid->err < LOC_INTEGRAL_START_ERR)
	{
		pid->integral += pid->err;  
        /*积分范围限定，防止积分饱和*/
		if(pid->integral > LOC_INTEGRAL_MAX_VAL)
		{
			pid->integral = LOC_INTEGRAL_MAX_VAL;
		}
		else if(pid->integral < -LOC_INTEGRAL_MAX_VAL)
		{
			pid->integral = -LOC_INTEGRAL_MAX_VAL;
		}
	}	

	/*PID算法实现*/
	pid->output_val = pid->Kp * pid->err +
	                  pid->Ki * pid->integral +
	                  pid->Kd * (pid->err - pid->err_last);

	/*误差传递*/
	pid->err_last = pid->err;

	/*返回当前实际值*/
	return pid->output_val;
}

c复制代码/**
  * @brief  速度PID算法实现
  * @param  actual_val:实际值
  *	@note 	无
  * @retval 通过PID计算后的输出
  */
#define SPE_DEAD_ZONE 5.0f /*速度环死区*/
#define SPE_INTEGRAL_START_ERR 100 /*积分分离时对应的误差范围*/
#define SPE_INTEGRAL_MAX_VAL 260   /*积分范围限定，防止积分饱和*/
float speed_pid_realize(PID *pid, float actual_val)
{
	/*计算目标值与实际值的误差*/
	pid->err = pid->target_val - actual_val;

	/* 设定闭环死区 */
	if( (pid->err>-SPE_DEAD_ZONE) && (pid->err<SPE_DEAD_ZONE ) )
	{
		pid->err = 0;
		pid->integral = 0;
		pid->err_last = 0;
	}
    
	/*积分项，积分分离，偏差较大时去掉积分作用*/
	if(pid->err > -SPE_INTEGRAL_START_ERR && pid->err < SPE_INTEGRAL_START_ERR)
	{
		pid->integral += pid->err;  
        /*积分范围限定，防止积分饱和*/
		if(pid->integral > SPE_INTEGRAL_MAX_VAL)
		{
			pid->integral = SPE_INTEGRAL_MAX_VAL;
		}
		else if(pid->integral < -SPE_INTEGRAL_MAX_VAL)
		{
			pid->integral = -SPE_INTEGRAL_MAX_VAL;
		}
	}	
	
	/*PID算法实现*/
	pid->output_val = pid->Kp * pid->err +
	                  pid->Ki * pid->integral +
	                  pid->Kd *(pid->err - pid->err_last);

	/*误差传递*/
	pid->err_last = pid->err;

	/*返回当前实际值*/
	return pid->output_val;
}

c复制代码//周期定时器的回调函数
void AutoReloadCallback()
{
	static uint32_t location_timer = 0;    // 位置环周期
	
	static __IO int encoderNow = 0;    /*当前时刻总计数值*/
    static __IO int encoderLast = 0;   /*上一时刻总计数值*/
	int encoderDelta = 0; /*当前时刻与上一时刻编码器的变化量*/
	float actual_speed = 0;  /*实际测得速度*/
	int actual_speed_int = 0;
	
	int res_pwm = 0;/*PID计算得到的PWM值*/
	static int i=0;
	
	/*【1】读取编码器的值*/
	encoderNow = read_encoder() + EncoderOverflowCnt*ENCODER_TIM_PERIOD;/*获取当前的累计值*/
	encoderDelta = encoderNow - encoderLast; /*得到变化值*/
	encoderLast = encoderNow;/*更新上次的累计值*/
	
	/*【2】位置PID运算，得到PWM控制值*/
	if ((location_timer++ % 2) == 0)
	{
		float control_val = 0;   /*当前控制值*/
		
		/*位置PID计算*/
		control_val = location_pid_realize(&pid_location, encoderNow);  
		
        /*目标速度值限制*/
		speed_val_protect(&control_val);

		/*设定速度PID的目标值*/
		set_pid_target(&pid_speed, control_val);    
	}
	  
	/* 转速(1秒钟转多少圈)=单位时间内的计数值/总分辨率*时间系数, 再乘60变为1分钟转多少圈 */
    actual_speed = (float)encoderDelta / TOTAL_RESOLUTION * 10 * 60;
    
	/*【3】速度PID运算，得到PWM控制值*/
	actual_speed_int = actual_speed;
	res_pwm = pwm_val_protect((int)speed_pid_realize(&pid_speed, actual_speed));
	
	/*【4】PWM控制电机*/
	set_motor_rotate(res_pwm);
	
	/*【5】数据上传到上位机显示*/
	set_computer_value(SEND_FACT_CMD, CURVES_CH1, &encoderNow, 1);   /*给通道1发送实际的电机【位置】值*/
}

复制代码IP地址：192.168.0.111

共享文件夹：file

yaml复制代码PS D:\file> python -m http.server 9090

arduino复制代码浏览器打开 http://192.168.0.111:9090

bash复制代码--bind：绑定的IP 和 端口，默认是本机ip，默认端口是8080

less复制代码PS D:\> python -m http.server -h
usage: server.py [-h] [--cgi] [--bind ADDRESS] [port]

positional arguments:
  port                  Specify alternate port [default: 8000]

optional arguments:
  -h, --help            show this help message and exit
  --cgi                 Run as CGI Server
  --bind ADDRESS, -b ADDRESS
                        Specify alternate bind address [default: all                        interfaces]
PS D:\>

bash复制代码python manage.py makemigrations

bash复制代码/usr/lib/python3/dist-packages/requests/__init__.py:80: RequestsDependencyWarning: urllib3 (1.26.4) or chardet (3.0.4) doesn't match a supported version!
  RequestsDependencyWarning)
Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    main()
  File "manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/base.py", line 330, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/base.py", line 371, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/base.py", line 85, in wrapped
    res = handle_func(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/django/core/management/commands/makemigrations.py", line 87, in handle
    loader = MigrationLoader(None, ignore_no_migrations=True)
  File "/usr/local/lib/python3.6/dist-packages/django/db/migrations/loader.py", line 53, in __init__
    self.build_graph()
  File "/usr/local/lib/python3.6/dist-packages/django/db/migrations/loader.py", line 255, in build_graph
    self.graph.validate_consistency()
  File "/usr/local/lib/python3.6/dist-packages/django/db/migrations/graph.py", line 195, in validate_consistency
    [n.raise_error() for n in self.node_map.values() if isinstance(n, DummyNode)]
  File "/usr/local/lib/python3.6/dist-packages/django/db/migrations/graph.py", line 195, in <listcomp>
    [n.raise_error() for n in self.node_map.values() if isinstance(n, DummyNode)]
  File "/usr/local/lib/python3.6/dist-packages/django/db/migrations/graph.py", line 58, in raise_error
    raise NodeNotFoundError(self.error_message, self.key, origin=self.origin)
django.db.migrations.exceptions.NodeNotFoundError: Migration comments.0001_initial dependencies reference nonexistent parent node ('tweets', '0002_auto_20210426_0742')

python复制代码import os

for root, dirs, files in os.walk('.'):
    if 'migrations' in dirs:
        dir = dirs[dirs.index('migrations')]
        for root_j, dirs_j, files_j in os.walk(os.path.join(root, dir)):
            for file_k in files_j:
                if file_k != '__init__.py':
                    dst_file = os.path.join(root_j, file_k)
                    print('>>> ', dst_file)
                    os.remove(dst_file)

java复制代码
@GetMapping("/")
public String process(Model model, HttpSession session) {
  @SuppressWarnings("unchecked")
  List<String> messages = (List<String>) session.getAttribute("springSession");

  if (messages == null) {
    messages = new ArrayList<>();
  }
  model.addAttribute("sessionMessages", messages);

  return "sessionTest";
}

@PostMapping("/persistSession")
public String persistMessage(@RequestParam("msg") String msg, HttpServletRequest request) {
  @SuppressWarnings("unchecked")
  List<String> messages = (List<String>) request.getSession().getAttribute("springSession");
  if (messages == null) {
    messages = new ArrayList<>();
    request.getSession().setAttribute("springSession", messages);
  }
  messages.add(msg);
  request.getSession().setAttribute("springSession", messages);
  return "redirect:/";
}

@PostMapping("/destroySession")
public String destroySession(HttpServletRequest request) {
  request.getSession().invalidate();
  return "redirect:/";
}

html复制代码<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Spring Boot Session Example</title>
</head>
<body>
<div>
    <form th:action="@{/persistSession}" method="post">
        <textarea name="msg" cols="40" rows="2"></textarea>
        <br> <input type="submit" value="保存" />
    </form>
</div>
<div>
    <h2>session列表</h2>
    <ul th:each="message : ${sessionMessages}">
        <li th:text="${message}">message</li>
    </ul>
</div>

<div>
    <form th:action="@{/destroySession}" method="post">
        <input type="submit" value="清空" />
    </form>
</div>
</body>
</html>

xml复制代码<dependency>
  <groupId>org.springframework.session</groupId>
  <artifactId>spring-session-core</artifactId>
  <version>2.5.0</version>
</dependency>

<dependency>
  <groupId>org.springframework.session</groupId>
  <artifactId>spring-session-jdbc</artifactId>
  <version>2.5.0</version>
</dependency>

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>8.0.18</version>
</dependency>

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

properties复制代码# 配置数据源相关内容
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/spring_learn?createDatabaseIfNotExist=true&autoReconnect=true&useSSL=false
spring.datasource.username=xxx
spring.datasource.password=xxx
spring.datasource.initialization-mode=always

# session类型选择jdbc
spring.session.store-type=jdbc
spring.session.jdbc.initialize-schema=always
# 指定表名
#spring.session.jdbc.table-name=SESSIONS
# 超时时间
spring.session.timeout=180s

sql复制代码CREATE TABLE `SPRING_SESSION` (
  `PRIMARY_ID` char(36) NOT NULL,
  `SESSION_ID` char(36) NOT NULL,
  `CREATION_TIME` bigint NOT NULL,
  `LAST_ACCESS_TIME` bigint NOT NULL,
  `MAX_INACTIVE_INTERVAL` int NOT NULL,
  `EXPIRY_TIME` bigint NOT NULL,
  `PRINCIPAL_NAME` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`PRIMARY_ID`),
  UNIQUE KEY `SPRING_SESSION_IX1` (`SESSION_ID`),
  KEY `SPRING_SESSION_IX2` (`EXPIRY_TIME`),
  KEY `SPRING_SESSION_IX3` (`PRINCIPAL_NAME`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC

sql复制代码CREATE TABLE `SPRING_SESSION_ATTRIBUTES` (
  `SESSION_PRIMARY_ID` char(36) NOT NULL,
  `ATTRIBUTE_NAME` varchar(200) NOT NULL,
  `ATTRIBUTE_BYTES` blob NOT NULL,
  PRIMARY KEY (`SESSION_PRIMARY_ID`,`ATTRIBUTE_NAME`),
  CONSTRAINT `SPRING_SESSION_ATTRIBUTES_FK` FOREIGN KEY (`SESSION_PRIMARY_ID`) REFERENCES `SPRING_SESSION` (`PRIMARY_ID`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci ROW_FORMAT=DYNAMIC

xml复制代码<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

<dependency>
  <groupId>org.springframework.session</groupId>
  <artifactId>spring-session-data-redis</artifactId>
</dependency>

properties复制代码spring.session.store-type=redis
spring.redis.host=127.0.0.1
spring.redis.port=6379

java复制代码
@Component
@Slf4j
public class AnnotationDrivenEventListener {

  @EventListener
  public void handleSessionCreated(SessionCreatedEvent sessionCreatedEvent) {
    String sessionId = sessionCreatedEvent.getSessionId();
    log.info("session id:{} created", sessionId);
  }

  @EventListener
  public void handleSessionDestroyed(SessionDestroyedEvent sessionDestroyedEvent) {
    String sessionId = sessionDestroyedEvent.getSessionId();
    log.info("session id:{} destroyed", sessionId);
  }
}

java复制代码private static int x = 0, y = 0;
private static int a = 0, b = 0;

Thread one = new Thread(new Runnable() {
    @Override
    public void run() {
        a = 1;
        x = b;
    }
});
Thread two = new Thread(new Runnable() {
    @Override
    public void run() {
        b = 1;
        y = a;
    }
});
two.start();
one.start();
one.join();
two.join();
System.out.println("x = "+x+", y = "+y);

java复制代码private static int x = 0, y = 0;
private static int a = 0, b = 0;

public static void main(String[] args) throws InterruptedException {
    int i = 0;
    for (; ; ) {
        i++;
        x = 0;
        y = 0;
        a = 0;
        b = 0;

        CountDownLatch latch = new CountDownLatch(3);

        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    latch.countDown();
                    latch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                a = 1;
                x = b;
            }
        });
        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    latch.countDown();
                    latch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                b = 1;
                y = a;
            }
        });
        thread2.start();
        thread1.start();
        latch.countDown();
        thread1.join();
        thread2.join();

        String result = "第" + i + "次（" + x + "," + y + ")";
        if (x == 0 && y == 0) {
            System.out.println(result);
            break;
        } else {
            System.out.println(result);
        }
    }
}

java复制代码public class Visibility {
   int a = 1;
   int b = 2;

   private void change() {
      a = 3;
      b = a;
   }


   private void print() {
      System.out.println("b=" + b + ";a=" + a);
   }

   public static void main(String[] args) {
      while (true) {
         Visibility visibility = new Visibility();
         // 线程1
         new Thread(() -> {
            try {
               Thread.sleep(1);
            } catch (InterruptedException e) {
               e.printStackTrace();
            }
            visibility.change();
         }).start();
		// 线程2
         new Thread(() -> {
            try {
               Thread.sleep(1);
            } catch (InterruptedException e) {
               e.printStackTrace();
            }
            visibility.print();
         }).start();
      }
   }
}

sql复制代码CREATE TABLE `staff` (
`id` BIGINT ( 11 ) AUTO_INCREMENT COMMENT '主键id',
`id_card` VARCHAR ( 20 ) NOT NULL COMMENT '身份证号码',
`name` VARCHAR ( 64 ) NOT NULL COMMENT '姓名',
`age` INT ( 4 ) NOT NULL COMMENT '年龄',
`city` VARCHAR ( 64 ) NOT NULL COMMENT '城市',
PRIMARY KEY ( `id`),
INDEX idx_city ( `city` )
) ENGINE = INNODB COMMENT '员工表';

csharp复制代码select name,age,city from staff where city = '深圳' order by age limit 10;

csharp复制代码## 打开optimizer_trace，开启统计
set optimizer_trace = "enabled=on";
## 执行SQL语句
select name,age,city from staff where city = '深圳' order by age limit 10;
## 查询输出的统计信息
select * from information_schema.optimizer_trace

sql复制代码show variables like 'max_length_for_sort_data';

ini复制代码## 修改排序数据最大单行长度为32
set max_length_for_sort_data = 32;
## 执行查询SQL
select name,age,city from staff where city = '深圳' order by age limit 10;

csharp复制代码## 打开optimizer_trace，开启统计
set optimizer_trace = "enabled=on";
## 执行SQL语句
select name,age,city from staff where city = '深圳' order by age limit 10;
## 查询输出的统计信息
select * from information_schema.optimizer_trace

csharp复制代码explain select name,age,city from staff where city = '深圳' order by age limit 10;

sql复制代码alter table staff add  index idx_city_age(city,age);
explain select name,age,city from staff where city = '深圳' order by age limit 10;

vbnet复制代码select * from A order by create_time;

vbnet复制代码select * from A order by create_time limit m;

css复制代码select * from A order by a limit 100000,10

sql复制代码select name,age from staff  order by age ,name desc limit 10;

sql复制代码CREATE TABLE `staff` (
  `id` bigint(11) NOT NULL AUTO_INCREMENT COMMENT '主键id',
  `id_card` varchar(20) NOT NULL COMMENT '身份证号码',
  `name` varchar(64) NOT NULL COMMENT '姓名',
  `age` int(4) NOT NULL COMMENT '年龄',
  `city` varchar(64) NOT NULL COMMENT '城市',
  PRIMARY KEY (`id`),
  KEY `idx_age_name` (`age`,`name` desc) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8 COMMENT='员工表';

csharp复制代码select * from staff where city in ('深圳') order by age limit 10;

csharp复制代码 explain select * from staff where city in ('深圳','上海') order by age limit 10;

java复制代码 Lock lock = ...;
 if (lock.tryLock()) {
   try {
     // manipulate protected state(处于保护状态的代码块)
   } finally {
     lock.unlock();
   }
 } else {
   // perform alternative actions（替代操作，不让线程阻塞）
 }

xml复制代码<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.75</version>
</dependency>

xml复制代码<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-annotations -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.12.1</version>
</dependency>

xml复制代码<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

java复制代码/**
 * @author DT开发者
 */
@Data
@EqualsAndHashCode(callSuper = false)
@AllArgsConstructor
@NoArgsConstructor
public class Person implements Serializable {
    
    private Integer id;
    
    private String name;
    
    private Date createTime;
}

java复制代码 public static void main(String[] args) {
    String json = "{\"createTime\":1621341922450,\"id\":1,\"name\":\"DT\"}";
    // 方式1: 将json字符串转为Java对象
    Person person = JSON.parseObject(json,Person.class);
    System.out.println("java对象->>>"+person);
    System.out.println("=========================================================");
    // 方式2: 将json字符串转为Java对象
    Person newPerson2 = JSONObject.parseObject(json, Person.class);
    System.out.println("java对象->>>"+newPerson2);
}

java复制代码JSON.parseObject(String,Object.class)
JSONObject.parseObject(String, Object.class)

java复制代码public static void main(String[] args) {
    // 创建Jackson核心对象 ObjectMapper
    ObjectMapper objectMapper = new ObjectMapper();
    String json = "{\"createTime\":1621341922450,\"id\":1,\"name\":\"DT\"}";
    try {
        Person person = objectMapper.readValue(json, Person.class);
        System.out.println("java对象->>>"+person);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

java复制代码public static void main(String[] args) {
     // gson无法正常将时间戳转化成date
     // 使用JSON内存树注册Date类型
     final Gson gson = new GsonBuilder()
     .registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
         @Override
         public Date deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext context) throws JsonParseException {
             return new Date(jsonElement.getAsJsonPrimitive().getAsLong());
         }
     }).create();

     String json = "{\"createTime\":1621341922450,\"id\":1,\"name\":\"DT\"}";
     Person person = gson.fromJson(json, Person.class);
     System.out.println("java对象->>>"+person);
 }

java复制代码public static void main(String[] args) {
     Person person = new Person(1,"DT",new Date());
     // 方式1：将对象转为json字符串
     String json = JSON.toJSONString(person);
     System.out.println("json字符串->>>"+json);
     System.out.println("=========================================================");
     // 方式2：将对象转为json字符串
     String json2 = JSONObject.toJSONString(person);
     System.out.println("json字符串->>>"+json2);
 }

java复制代码JSONObject.toJSONString(String)
JSON.toJSONString(String)

java复制代码public static void main(String[] args) {
     // 创建Jackson核心对象 ObjectMapper
     ObjectMapper objectMapper = new ObjectMapper();
     Person person = new Person(1,"DT",new Date());
     try {
         String json = objectMapper.writeValueAsString(person);
         System.out.println("json字符串->>>"+json);
     } catch (JsonProcessingException e) {
         e.printStackTrace();
     }
 }

java复制代码public static void main(String[] args) {
    Gson gson = new Gson();
    Person person = new Person(1,"DT",new Date());
    String json = gson.toJson(person);
    System.out.println("json字符串->>>"+json);
}

java复制代码public static void main(String[] args) {
    List<Person> personList = new ArrayList<>();
    personList.add(new Person(1,"DT",new Date()));
    personList.add(new Person(2,"DT1",new Date()));
    personList.add(new Person(3,"DT2",new Date()));
    String json = JSONObject.toJSONString(personList);
    JSONArray jsArr = JSONObject.parseArray(json);
    System.out.println(jsArr);
}

java复制代码JSONObject.parseArray(json)

java复制代码 public static void main(String[] args) {
   List<Person> personList = new ArrayList<>();
    personList.add(new Person(1,"DT",new Date()));
    personList.add(new Person(2,"DT1",new Date()));
    personList.add(new Person(3,"DT2",new Date()));
    String json = JSONObject.toJSONString(personList);
    JSONArray jsArr = JSONObject.parseArray(json);
    // 遍历方式1
    jsArr.stream().forEach(json1 ->{
        System.out.println(json1.toString());
    });
    // 遍历方式2
    for (Object o : jsArr) {
        JSONObject obj = (JSONObject) o;
        System.out.println("取到id->>>" + obj.get("id"));
        // 判断是否存在key
        System.out.println("key是否存在->>>"+obj.containsKey("name1"));
        // 判断是否存在值
        System.out.println("value是否存在->>>"+obj.containsValue(obj.get("id")));
    }
}

java复制代码public static void main(String[] args) throws JsonProcessingException {
    // 将JSON数组转换为array对象
    ObjectMapper mapper = new ObjectMapper();
    String json = "[{\"id\":1,\"name\":\"张三\",\"createTime\":1622719597081}, {\"id\":2,\"name\":\"李四\",\"createTime\":1622719597081}]";
    // 方式1
    Person[] pp1 = mapper.readValue(json, Person[].class);
    for (Person person : pp1) {
        System.out.println(person);
    }
    // 方式2
    List<Person> ppl2 = Arrays.asList(mapper.readValue(json, Person[].class));
    ppl2.stream().forEach(System.out::println);
    // 方式3
    List<Person> pp3 = mapper.readValue(json, new TypeReference<List<Person>>() {});
    pp3.stream().forEach(System.out::println);
}

java复制代码```java
public static void main(String[] args) {
    // gson无法正常将时间戳转化成date
    // 使用JSON内存树注册Date类型
    final Gson gson = new GsonBuilder()
            .registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
                @Override
                public Date deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext context) throws JsonParseException {
                    return new Date(jsonElement.getAsJsonPrimitive().getAsLong());
                }
            }).create();
    
    String json = "[{\"id\":1,\"name\":\"张三\",\"createTime\":1622719597081}, {\"id\":2,\"name\":\"李四\",\"createTime\":1622719597081}]";
    Type type = new TypeToken<ArrayList<Person>>(){}.getType();
    List<Person> personList = gson.fromJson(json, type);
    personList.stream().forEach(System.out::println);
}

java复制代码public static void main(String[] args) {
   List<Person> personList = new ArrayList<>();
    personList.add(new Person(1,"DT",new Date()));
    personList.add(new Person(2,"DT1",new Date()));
    personList.add(new Person(3,"DT2",new Date()));
    String json = JSONObject.toJSONString(personList);
    System.out.println("json->>>"+json);
}

java复制代码public static void main(String[] args) throws JsonProcessingException {
   ObjectMapper objectMapper = new ObjectMapper();
    List<Person> personList = new ArrayList<>();
    personList.add(new Person(1,"DT",new Date()));
    personList.add(new Person(2,"DT1",new Date()));
    personList.add(new Person(3,"DT2",new Date()));
    String json = objectMapper.writeValueAsString(personList);
    System.out.println("json->>>"+json);
}

java复制代码public static void main(String[] args) {
    Gson gson = new Gson();
    List<Person> personList = new ArrayList<>();
    personList.add(new Person(1,"DT",new Date()));
    personList.add(new Person(2,"DT1",new Date()));
    personList.add(new Person(3,"DT2",new Date()));
    String json = gson.toJson(personList);
    System.out.println("json->>>"+json);
}