我所用到的Java8-续

工作之余，总结了下Java8的相关运用，主要是关于Stream流的。还有一些工作总结笔记。

Stream流操作

//map集合获取value  获取新方式
map.getOrDefault(goodsId, 0L)
default V getOrDefault(Object key, V defaultValue) {
   V v;
   return (((v = get(key)) != null) || containsKey(key)) ? v : defaultValue;
}
//flatMap使用
List<OrderSetDetail> setDetails = order.getDetails().stream()
                .filter(x -> CollectionUtils.isNotEmpty(x.getOrderSetDetails()))
                .flatMap(orderDetail -> orderDetail.getOrderSetDetails().stream())
                .collect(Collectors.toList());
//distinct
distinct主要用来去重，以下代码片段使用 distinct 对元素进行去重：
List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
numbers.stream().distinct().forEach(System.out::println);
//3,2,7,5
//groupingBy&count分组统计
Map<String, Long> collect = lists.stream().collect(Collectors
                .groupingBy(Student::getName, Collectors.counting()));
//Java8 Map集合遍历
 Map<String, Integer> updateStockMap = Optional.ofNullable(updateActivityStockList).orElseGet(ArrayList::new)
                .stream().collect(Collectors.groupingBy(UpdateActivityStock::getId,
                        Collectors.reducing(Integer.valueOf(0), UpdateActivityStock::getStock, Integer::sum)));
updateStockMap.forEach((id, stockNum) -> {
    ActivityStock oldStock = stockMap.get(id);
    if (oldStock != null) {
        ActivityStock stock = new ActivityStock();
        stock.setId(id);
        stock.setStock(stockNum);
    }
});
//Java8 Map集合遍历2
public class IterateHashMapExample {  
    public static void main(String[] args) {  
        Map < Integer, String > coursesMap = new HashMap < Integer, String > ();  
        coursesMap.put(1, "C");  
        coursesMap.put(2, "C++");  
        coursesMap.put(3, "Java");  
        coursesMap.put(4, "Spring Framework");  
        coursesMap.put(5, "Hibernate ORM framework");  
        // 5. 使用 Stream API 遍历 HashMap  
        coursesMap.entrySet().stream().forEach((entry) - > {  
            System.out.println(entry.getKey());  
            System.out.println(entry.getValue());  
        });  
    }
}
// java8之后。上面的操作可以简化为一行，若key对应的value为空，会将第二个参数的返回值存入并返回
Object key2 = map.computeIfAbsent("key", k -> new Object());
//相当于：
  if(map.get("key") == null) {
      map.put("key", new Object());
  } 
//List转Map(key去重)
Map<String, Student> studentMap = list1.stream().collect(Collectors.toMap(Student::getName, value -> value, (a1, a2) -> a1));

Example条件查询

public Activity getEffectiveActivity() {
   Date now = new Date();
   Example example = new Example(Activity.class);
   example.createCriteria().andEqualTo("isEnable", SystemConstants.YES)
         .andEqualTo("activityType", ActivityType.RUN)
         .andLessThanOrEqualTo("startDate", now)
         .andGreaterThanOrEqualTo("endDate", now);
   List<Activity> activities = listAllByExample(example);
   if(!activities.isEmpty()) {
      return activities.get(0);
   } else {
      return null;
   }
}
//单一计算
SpokesmanUser entity = new SpokesmanUser();
entity.setParentId(userId);
return this.dao.selectCount(entity);// 租户之间用户id保证唯一
//多条件统计
Example example = new Example(SpokesmanUser.class);
Example.Criteria criteria = example.createCriteria();
criteria.andEqualTo("parentId", userId);
criteria.andNotEqualTo("id", excludChildId);
return this.dao.selectCountByExample(example);// 租户之间用户id保证唯一
//sql拼接
if (query.getStartTime() != null && query.getEndTime() != null
      && query.getEndTime().after(query.getStartTime())) {
   String startTime = DateTimeUtils.formatDateTime(query.getStartTime());
   String endTime = DateTimeUtils.formatDateTime(query.getEndTime());
   criteria.andCondition(String.format(
         "((start_time >= '%s' AND '%s' >= start_time) OR ('%s' >= start_time AND end_time >= '%s') OR (end_time >= '%s' AND '%s' >= end_time))",
         startTime, endTime, startTime, endTime, startTime, endTime));
}
public List<Entity> listByCsId(String csId) {
    Example example = new Example(Entity.class);
    example.createCriteria().andEqualTo("csId", csId)
            .andEqualTo("isAssignCs", SystemConstants.YES)
            .andEqualTo("isEndSession", SystemConstants.NO);
    example.setOrderByClause("update_date DESC");
    return this.listAllByExample(example);
}
//updateByExample使用
ChatSession updateEntity = new ChatSession();
updateEntity.setId(chatSession.getId());
updateEntity.setServiceEndDate(new Date());
updateEntity.setIsEndSession(SystemConstants.YES);
updateEntity.setRemark(remark);
updateEntity.setUpdateDate(new Date());
updateEntity.setUpdateBy(operator);
Example example = new Example(ChatSession.class);
example.createCriteria().andEqualTo("id", chatSession.getId()).andEqualTo("isEndSession", SystemConstants.NO);
int result = chatSessionRepository.updateByExample(updateEntity, example);

使用SecureRandom

由于java.util.Random类依赖于伪随机数生成器，因此该类和相关的java.lang.Math.random（）方法不应用于安全关键应用程序或保护敏感数据。 在这种情况下，应该使用依赖于加密强随机数生成器（RNG）的java.security.SecureRandom类。
PRNG(伪随机数)：
伪随机数， 计算机不能生成真正的随机数，而是通用一定的方法来模拟随机数。伪随机数有一部分遵守一定的规律，另一部分不遵守任何规律。
RNG(随机数)：
随机数是由“随机种子”产生的，“随机种子”是一个无符号整形数。
反例：
Random random = new Random(); // Questionable use of Random
byte bytes[] = new byte[20];
random.nextBytes(bytes);
正例：
SecureRandom random = new SecureRandom(); 
byte bytes[] = new byte[20];

arthas命令

wget https://alibaba.github.io/arthas/arthas-boot.jar
#启动示例
java -jar arthas-boot.jar
#获取trace调用链
trace -j com.xxx.xxx.application.command.WechatLotteryRunService drawPrize '#cost > 300'
# 获取Servlet调用路径，并过滤掉JDK的函数
trace -j javax.servlet.Servlet * >> test.log
# 获取Filter调用路径，并过滤掉JDK的函数
trace -j javax.servlet.Filter * >> test.log
trace -j org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient * >> test.log
watch org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient execute "{params,target,throwExp,returnObj}" -e -x 2 -b -s -n 2
trace -j com.xxx.erp.action.autocalculate.WarehouseAction | com.xxx.erp.action.autocalculate.ExpressAction * '#cost > 100'
# 录制重放
tt -t -n 2 org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient execute
# 查看id
tt -l
# 详情
tt -i 1000
# 重放
tt -i 1000 -p
# 获取spring 容器
tt -t org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter invokeHandlerMethod
tt -i 1000 -w 'target.getApplicationContext()'
tt -i 1000 -w 'target.getApplicationContext().getBean("helloWorldService").getHelloMessage()'
ognl '#context=@com.yjh.mushroom.common.spring.SpringContextHolder@applicationContext, #context.getBean("idGenerator").nextId()'
# 快速排查Spring Boot应用404/401问题
stack -E javax.servlet.http.HttpServletResponse sendError|setStatus params[0]==404
# 800错误排查
watch com.xxx.xxx.framework.spring.web.GlobalExceptionHandler handleUncatchedException params[2]
#oms 异常排查
watch com.xxx.xxx.main.order.web.OrderController * "{clazz.name, params[0],throwExp}" -e -x 2
#oms调用eureka地址检查
watch com.netflix.client.ClientRequest replaceUri "params[0]"
#oms数据库连接排查
watch com.mysql.jdbc.MysqlIO doHandshake "{params[0],params[1],params[2],target.host}" -b
#oms订单任务判断
watch com.xxx.oms.sync.domain.service.PlatformDomainEventService handlePendingEvent params[0]

自动化脚本模拟并发

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cd wrk/wrk-master/
wrk -t4 -c1000 -d60s -T10s --latency http://localhost:9016 --script=scripts/20190621/方法名.lua

时间差计算

1	long diffMinutes = ChronoUnit.MINUTES.between(Instant.now(), sendDate.toInstant());

Java8 Duration

1 2	Duration duration = Duration.ofDays(verifyDays * -1); Instant lastValidDate = Instant.now().plus(duration);

微信接口调用实例

RestTemplate调用接口示列

JSONObject param = new JSONObject();
param.put("type", request.getData()); // 素材的类型，图片（image）、视频（video）、语音 （voice）、图文（news）
param.put("offset", (request.getPageNo() - 1) * request.getPageSize()); // 从全部素材的该偏移位置开始返回，0表示从第一个素材 返回
param.put("count", request.getPageSize()); // 返回素材的数量，取值在1到20之间
RestTemplate restTemplate = new RestTemplate();
restTemplate.getMessageConverters().set(1, new StringHttpMessageConverter(StandardCharsets.UTF_8)); // 处理中文乱码
ResponseEntity<String> re = restTemplate.postForEntity("https://api.weixin.qq.com/cgi-bin/material/batchget_material?access_token=" + token, param, String.class);
if (HttpStatus.OK.equals(re.getStatusCode()) && re.getBody() != null) {
    JSONObject result = JSONObject.parseObject(re.getBody());
    if (!result.containsKey("errcode")) {
        pageInfo.setTotal(result.getLong("total_count"));
        List<MpMaterialVO> list = Lists.newArrayList();
        JSONArray itemArr = result.getJSONArray("item");
        itemArr.forEach(item -> list.add(new MpMaterialVO((JSONObject) item)));
        pageInfo.setList(list);
        return pageInfo;
    }
}

httpclient调用实例

public static String sendGet(String url, PayAccountBizCodeType bizCodeType) {
        HttpGet httpGet = new HttpGet(url);
        httpGet.setHeader("Content-Type", "application/json;charset=UTF-8");
        httpGet.setHeader("Accept", "application/json");
        httpGet.setHeader("User-Agent", getUserAgent());
        httpGet.setHeader("Authorization", getAuthorization("GET", url, "", bizCodeType));
        String result = executeRequest(httpGet);
        logger.info("调用微信GET接口，url:{} ,result:{}", url, result);
        return result;
    }
private static String executeRequest(HttpUriRequest request) {
    CloseableHttpClient client = HttpClients.createDefault();
    String result = "";
    try {
        CloseableHttpResponse response = client.execute(request);
        HttpEntity entity = response.getEntity();
        result = EntityUtils.toString(entity, "UTF-8");
    } catch (IOException e) {
        logger.error("调用微信接口失败，失败原因：" + e.getMessage(), e);
    } finally {
        try {
            client.close();
        } catch (IOException e) {
            logger.error("关闭httpclient失败，失败原因:{}", e);
        }
    }
    return result;
}

获取Json数据

public MpMaterialVO(JSONObject jsonObject) {
    this.mediaId = jsonObject.getString("media_id");
    JSONObject news = (JSONObject) jsonObject.getJSONObject("content").getJSONArray("news_item").get(0);
    this.title = news.getString("title");
    this.digest = news.getString("digest");
    this.thumbUrl = news.getString("thumb_url");
}

Json与VO相互转换

/**
 * 对应VO转为内容json
 */
public void voToJson() {
    if (type == MaterialTemplateTypeEnum.MINI_CARD) {
        contentJson = JsonUtils.toJsonString(miniCardVO);
    } else if (type == MaterialTemplateTypeEnum.ADVANCED_IMAGE_TEXT) {
        contentJson = JsonUtils.toJsonString(advancedImageTextVO);
    } else {
        contentJson = JsonUtils.toJsonString(content);
    }
}
/**
 * 内容json转为对应VO
 */
public void jsonToVO() {
    if (type == MaterialTemplateTypeEnum.MINI_CARD) {
        miniCardVO = JsonUtils.toBean(contentJson, MiniCardVO.class);
    } else if (type == MaterialTemplateTypeEnum.ADVANCED_IMAGE_TEXT) {
        advancedImageTextVO = JsonUtils.toBean(contentJson, AdvancedImageTextVO.class);
    } else {
        content = JsonUtils.toBean(contentJson, String.class);
    }
}

微信发送图文消息举例

{
    "touser":"OPENID",
    "msgtype":"news",
    "news":{
        "articles": [
         {
             "title":"Happy Day",
             "description":"Is Really A Happy Day",
             "url":"URL",
             "picurl":"PIC_URL"
         }
         ]
    }
}
public JSONObject initAdvancedImageText(AdvancedImageTextVO advancedImageTextVO) {
    JSONObject param = new JSONObject();
    param.put(MSG_TYPE, "news");
    JSONObject news = new JSONObject();
    JSONArray articles = new JSONArray();
    JSONObject article = new JSONObject();
    article.put(TITLE, advancedImageTextVO.getTitle());
    article.put("description", advancedImageTextVO.getDescription());
    article.put("url", advancedImageTextVO.getHref());
    article.put("picurl", advancedImageTextVO.getUrl());
    articles.add(article);
    news.put("articles", articles);
    param.put("news", news);
    return param;
}

mybatis的Sql使用

xml配置

<sql id="memberColumns">
              a.id AS "id",
   a.card_no AS "cardNo",
   a.mobile AS "mobile",
   a.login_name AS "loginName",
   a.password AS "password",
   a.status AS "status",
   a.sex AS "sex",
   a.birthday AS "birthday",
   a.nick_name AS "nickName",
   a.icon AS "icon",
   a.is_created_order AS "isCreatedOrder",
   a.binding_status AS "bindingStatus",
   a.province AS "province",
   a.city AS "city",
   a.create_date AS "createDate",
   a.create_by AS "createBy",
   a.update_date AS "updateDate",
   a.update_by AS "updateBy",
   a.del_flag AS "delFlag",
   a.remarks AS "remarks",
   a.tenant_id AS "tenantId",
   a.ext_tenant_id AS "extTenantId"
</sql>
   <select id="listMember" resultMap="memberCO">
       SELECT b.channel,
       <include refid="memberColumns"/>
       ....
   </select>

java使用

1	List<memberCO> list = memberChannelExtRepository.listMember("参数");

Java ES api相关使用

//范围查询
if (null != query.getCancelTimeStart()) {
    RangeQueryBuilder cancelTimeStartQuery = QueryBuilders.rangeQuery("cancelTime")
    .gte(DateTimeUtils.formatDateTime(query.getCancelTimeStart()));
    filter.must(cancelTimeStartQuery);
}
if (null != query.getCancelTimeEnd()) {
    RangeQueryBuilder cancelTimeEndQuery = QueryBuilders.rangeQuery("cancelTime")
    .lte(DateTimeUtils.formatDateTime(query.getCancelTimeEnd()));
    filter.must(cancelTimeEndQuery);
}
//集合查询
if (ValidateUtils.isNotEmptyCollection(query.getPaymentStatuses())) {
    List<String> paymentStatuses = query.getPaymentStatuses().stream()
        .map(paymentStatus -> paymentStatus.toString()).collect(Collectors.toList());
    TermsQueryBuilder paymentStatusesQuery = QueryBuilders.termsQuery("paymentStatus", paymentStatuses);
    filter.must(paymentStatusesQuery);
}
//精确查询
 TermsQueryBuilder originalExpressIdQuery = QueryBuilders
                    .termsQuery("originalExpressId", query.getOriginalExpressId());
            filter.must(originalExpressIdQuery);
//
QueryBuilder queryBuilder = QueryBuilders.wildcardQuery("user", "ki*hy");
//模糊查询
RegexpQueryBuilder externalCodeQuery = QueryBuilders.regexpQuery("externalCode",
                    “*”+ query.getExternalCode() + “*”);
WildcardQueryBuilder externalCodeQuery = QueryBuilders.wildcardQuery("externalCode",
                    "*"+query.getExternalCode()+"*");

parseInt与valueOf

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Integer dailySignPointToInt = Integer.parseInt(resultData);
//推荐2，有缓存
Integer dailySignPointToInt = Integer.valueOf(resultData);

Arrays.asList()与Collections.singletonList()

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Arrays.asList(strArray)返回值是仍然是一个可变的集合，但是返回值是其内部类，不具有add方法，可以通过set方法进行增加值，默认长度是10
Collections.singletonList()返回的同样是不可变的集合，但是这个长度的集合只有1，可以减少内存空间。但是返回的值依然是Collections的内部实现类，同样没有add的方法，调用add，set方法会报错

@Transient

@Transient表示该属性并非一个到数据库表的字段的映射,ORM框架将忽略该属性. 如果一个属性并非数据库表的字段映射,就务必将其标示为@Transient,否则,ORM框架默认其注解为@Basic

本地导出文件测试

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/octet-stream' --header 'X-Client-Id: swagger' --header 'X-Client-Token: 852311eac642cbf8059928c371784461' --header 'X-Tenant-Id: newretail' --header 'X-Ext-Tenant-Id: 1275854953286784' -d '{}' 'http://localhost:9017/api/earningRuleRetail/exportExcel' -o aa.xlsx

Kafka操作

//消费者
bin/windows/kafka-console-consumer.bat --zookeeper localhost:2181 --topic lvshen_demo_test --from-beginning
//生产者
bin/windows/kafka-console-producer.bat --broker-list localhost:9092 --topic lvshen_demo_test

判断小程序或h5

1	String clientType = ServletUtils.getRequest().getHeader("X-Client-Type");

InitializingBean

InitializingBean接口为bean提供了初始化方法的方式，它只包括afterPropertiesSet方法，凡是继承该接口的类，在初始化bean的时候都会执行该方法。
//示例
public class SensitiveWordFilterHelper implements InitializingBean {		
	@Override
	public void afterPropertiesSet() throws Exception {
		refreshAllWord();
	}
	...
}

kafka重试

1. new KafkaProducer()后创建一个后台线程KafkaThread扫描RecordAccumulator中是否有消息； 
2. 调用KafkaProducer.send()发送消息，实际上只是把消息保存到RecordAccumulator中； 
3. 后台线程KafkaThread扫描到RecordAccumulator中有消息后，将消息发送到kafka集群； 
4. 如果发送成功，那么返回成功； 
5. 如果发送失败，那么判断是否允许重试。如果不允许重试，那么返回失败的结果；如果允许重试，把消息再保存到RecordAccumulator中，等待后台线程KafkaThread扫描再次发送；

ArrayDeque方法（双队列）

addFirst(E e)

//addFirst(E e)
public void addFirst(E e) {
    if (e == null)//不允许放入null
    throw new NullPointerException();
    elements[head = (head - 1) & (elements.length - 1)] = e;//2.下标是否越界
    if (head == tail)//1.空间是否够用
    doubleCapacity();//扩容
}

时间单位转换

//3600分钟 转换成 小时 是多少
System.out.println(TimeUnit.HOURS.convert(3600, TimeUnit.MINUTES));
//3600分钟 转换成 天 是多少
System.out.println(TimeUnit.DAYS.convert(3600, TimeUnit.MINUTES));
//3600分钟 转换成 秒 是多少
System.out.println(TimeUnit.SECONDS.convert(3600, TimeUnit.MINUTES));

事务结束后代码处理逻辑

1	afterTransactionExecutor.execute(() -> clearCacheCommodityByIds(ids));

地址路径为方法参数

@PostMapping("/changeSort/{id}/{type}")
@ApiOperation(value = "调整排序 TOTOP/UP", tags = TagConstant.PC)
@RequiresPermissions("xxx-commodity:commodityParam:edit")
public void changeSort(@PathVariable("id") String id, @PathVariable("type") String type) {
    Assert.hasLength(id, "属性id有误");
    commodityParamQueryService.get(id);
    commodityParamService.changeSort(id, type);
}

批量操作tips

java

//批量操作时，先将索引字段排序，有利于避免死锁.按顺序加锁不会产生锁环
stockAllocateList.sort(Comparator.comparing(StockAllocate::getSkuId));
stockAllocateList.forEach(item -> {
    int size = this.dao.updateSubAllocateStock(item);
    if (size <= 0) {
        throw new BusinessException("stockSubAllocate_error", stockAllocateVOS.toString());
    }
});

sql

<update id="updateSubAllocateStock" >
   update stock set allocate_stock = allocate_stock - #{commodityNumber}
   where sku_id=#{skuId} and allocate_stock >= #{commodityNumber}
</update>

锁查询

select * from information_schema.innodb_locks;
show engine innodb status;
SELECT * FROM information_schema.innodb_lock_waits;
SHOW VARIABLES LIKE 'optimizer_trace';
SET optimizer_trace="enabled=on";
SELECT * FROM student WHERE name = 'fly';
SELECT * FROM information_schema.OPTIMIZER_TRACE;
--MySQL监控
-- 开启标准监控
CREATE TABLE innodb_monitor (a INT) ENGINE=INNODB;
-- 关闭标准监控
DROP TABLE innodb_monitor;
-- 开启锁监控
CREATE TABLE innodb_lock_monitor (a INT) ENGINE=INNODB; 
-- 关闭锁监控
DROP TABLE innodb_lock_monitor;
--在 MySQL 5.6.16 之后，可以通过设置系统参数来开启锁监控
-- 开启标准监控
set GLOBAL innodb_status_output=ON;
-- 关闭标准监控
set GLOBAL innodb_status_output=OFF;
-- 开启锁监控
set GLOBAL innodb_status_output_locks=ON;
-- 关闭锁监控
set GLOBAL innodb_status_output_locks=OFF;
--MySQL 提供了一个系统参数 innodb_print_all_deadlocks 专门用于记录死锁日志，当发生死锁时，死锁日志会记录到 MySQL 的错误日志文件中
set GLOBAL innodb_print_all_deadlocks=ON;

MySQL死锁模拟

--事务A
mysql> begin;
Query OK, 0 rows affected
--执行顺序 1
mysql> update student set age=31
 where name = 'fly';
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0
--执行顺序 3
mysql> update student set age=32 where name = 'alan';
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0
--事务B
mysql> begin;
Query OK, 0 rows affected (0.00 sec)
--执行顺序 2
mysql> update student set age=31 where name = 'alan';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0
--执行顺序 4
mysql> update student set age=21 where name = 'fly';
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction

使用Mybatis操作

注意不要先查询再操作

删除

//推荐
@Test
public void testDelete() {
   Student student = new Student();
   student.setName("Hare");
   int delete = studentRepository.delete(student);
   log.info("删除{}条数据",delete);
}
//不推荐
public void testDelete() {
   Student student = studentRepositoryg.getByName("Hare");
   int delete = studentRepository.delete(student);
   log.info("删除{}条数据",delete);
}

更新

//更新
@Test
public void testUpdate() {
   Student student = new Student();
   student.setId("2073678416402304");
   student.setAge(26);
   studentRepository.update(student);
   log.info("test is success!!!");
}
//按条件更新
@Test
public void testUpdateByExample() {
   //修改内容
   Student student = new Student();
   student.setAge(27);
   //修改条件
   Example example = new Example(Student.class);
   Example.Criteria criteria = example.createCriteria();
   criteria.andIn("name", ImmutableList.of("fly","lvshen"));
   int i = studentRepository.updateByExample(student, example);
   log.info("test is success!!!{}",i);
}
//不推荐
@Test
public void testUpdate() {
   Student student = studentRepository.get("2073678416402304");
   studentRepository.update(student);
   log.info("test is success!!!");
}

Linux命令

#内存信息
jmap -F -dump:format=b,file=test.bin 22829（pid）
#堆信息
jstat -gcutil 22829（pid）

我所用到的Java8-续

Stream流操作

Example条件查询

使用SecureRandom

arthas命令

自动化脚本模拟并发

时间差计算

Java8 Duration

微信接口调用实例

RestTemplate调用接口示列

httpclient调用实例

获取Json数据

Json与VO相互转换

微信发送图文消息举例

mybatis的Sql使用

xml配置

java使用

Java ES api相关使用

parseInt与valueOf

Arrays.asList()与Collections.singletonList()

@Transient

本地导出文件测试

Kafka操作

判断小程序或h5

InitializingBean

kafka重试

ArrayDeque方法（双队列）

addFirst(E e)

时间单位转换

事务结束后代码处理逻辑

地址路径为方法参数

批量操作tips

java

sql

锁查询

MySQL死锁模拟

使用Mybatis操作

删除

更新

Linux命令

谢谢大爷~