十二條後端開發經驗分享,純乾貨,總有一條你不知道

来源:https://www.cnblogs.com/wayn111/archive/2022/11/30/16939538.html
-Advertisement-
Play Games

前言 本文是博主從事後端開發以來,對公司、個人項目的經驗總結,包含代碼編寫、功能推薦、第三方庫使用及優雅配置等,希望大家看到都能有所收穫 博主github地址: https://github.com/wayn111 一. 優雅的進行線程池異常處理 在Java開發中,線程池的使用必不可少,使用無返回值 ...


前言

本文是博主從事後端開發以來,對公司、個人項目的經驗總結,包含代碼編寫、功能推薦、第三方庫使用及優雅配置等,希望大家看到都能有所收穫

一. 優雅的進行線程池異常處理

在Java開發中,線程池的使用必不可少,使用無返回值 execute() 方法時,線程執行發生異常的話,需要記錄日誌,方便回溯,一般做法是線上程執行方法內 try/catch 處理,如下:

@Test
public void test() throws Exception {
    ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(5, 10, 60,
            TimeUnit.SECONDS, new ArrayBlockingQueue<>(100000));
    Future<Integer> submit = threadPoolExecutor.execute(() -> {
        try {
            int i = 1 / 0;
            return i;
        } catch (Exception e) {
            log.error(e.getMessage(), e);
            return null;
        }
    });
}

但是當線程池調用方法很多時,那麼每個線程執行方法內都要 try/catch 處理,這就不優雅了,其實ThreadPoolExecutor類還支持傳入 ThreadFactory 參數,自定義線程工廠,在創建 thread 時,指定 setUncaughtExceptionHandler 異常處理方法,這樣就可以做到全局處理異常了,代碼如下:

ThreadFactory threadFactory = r -> {
    Thread thread = new Thread(r);
    thread.setUncaughtExceptionHandler((t, e) -> {
        // 記錄線程異常
        log.error(e.getMessage(), e);
    });
    return thread;
};
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(5, 10, 60,
        TimeUnit.SECONDS, new ArrayBlockingQueue<>(100000),
        threadFactory);
threadPoolExecutor.execute(() -> {
    log.info("---------------------");
    int i = 1 / 0;
});

二. 線程池決絕策略設置錯誤導致業務介面執行超時

先介紹下線程池得四種決絕策略

  • AbortPolicy:丟棄任務並拋出RejectedExecutionException異常,這是線程池預設的拒絕策略
  • DiscardPolicy:丟棄任務,但是不拋出異常。如果線程隊列已滿,則後續提交的任務都會被丟棄,且是靜默丟棄。
    使用此策略,可能會使我們無法發現系統的異常狀態。建議是一些無關緊要的業務採用此策略
  • DiscardOldestPolicy:丟棄隊列最前面的任務,然後重新提交被拒絕的任務。此拒絕策略,是一種喜新厭舊的拒絕策略。是否要採用此種拒絕策略,還得根據實際業務是否允許丟棄老任務來認真衡量。
  • CallerRunsPolicy:由調用線程處理該任務

如下是一個線上業務介面使用得線程池配置,決絕策略採用 CallerRunsPolicy

// 某個線上線程池配置如下
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                50, // 最小核心線程數
                50, // 最大線程數,當隊列滿時,能創建的最大線程數
                60L, TimeUnit.SECONDS, // 空閑線程超過核心線程時,回收該線程的最大等待時間
                new LinkedBlockingQueue<>(5000), // 阻塞隊列大小,當核心線程使用滿時,新的線程會放進隊列
            new CustomizableThreadFactory("task"), // 自定義線程名
                new ThreadPoolExecutor.CallerRunsPolicy() // 線程執行的拒絕策略
        );

在某些情況下,子線程任務調用第三方介面超時,導致核心線程數、最大線程數占滿、阻塞隊列占滿的情況下執行拒絕策略時,由於使用 CallerRunsPolicy 策略,導致業務線程執行子任務時繼續超時,進而導致介面執行異常,這種情況下,考慮到子線程任務得重要性,不是很重要得話,可以使用 DiscardPolicy 策略,要是很重要,可以發送到消息隊列中持久化子線程任務數據待後續處理

三. 優雅的單例模式懶載入幫助類代碼實現

博主推薦通過靜態內部類實現單例模式,並實現懶載入效果,代碼如下

// 使用靜態內部類完成單例模式封裝,避免線程安全問題,避免重覆初始化成員屬性  
@Slf4j  
public class FilterIpUtil {  
  
    private FilterIpUtil() {  
    }  
  
    private List<String> strings = new ArrayList<>();  
  
    // 代碼塊在FilterIpUtil實例初始化時才會執行  
    {  
    
        // 在代碼塊中完成文件的第一次讀寫操作,後續不再讀這個文件
        System.out.println("FilterIpUtil init");  
        try (InputStream resourceAsStream = FilterIpUtil.class.getClassLoader().getResourceAsStream("filterIp.txt")) {  
            // 將文件內容放到string集合中  
            IoUtil.readUtf8Lines(resourceAsStream, strings);  
        } catch (IOException e) {  
            log.error(e.getMessage(), e);  
        }  
    }  
  
    public static FilterIpUtil getInstance() {  
        return InnerClassInstance.instance;  
    }  
    // 使用內部類完成單例模式,由jvm保證線程安全  
    private static class InnerClassInstance {  
        private static final FilterIpUtil instance = new FilterIpUtil();  
    }  
  
    // 判斷集合中是否包含目標參數  
    public boolean isFilter(String arg) {  
        return strings.contains(arg);  
    }  
  
}

四. 使用ip2region實現請求地址解析

在博主之前公司得項目中,ip解析是調用淘寶IP還有聚合IP介面獲取結果,通常耗時200毫秒左右,並且介面不穩定時而會掛。都會影響業務介面耗時,後來在 github 上瞭解到 ip2region 這個項目,使用本地ip庫查詢,查詢速度微秒級別, 精準度能達到90%,但是ip庫還是有少部分ip信息不准,建議資料庫中把請求ip地址保存下來。簡介如下:

ip2region v2.0 - 是一個離線IP地址定位庫和IP定位數據管理框架,10微秒級別的查詢效率,提供了眾多主流編程語言的 xdb 數據生成和查詢客戶端實現基於 xdb 文件的查詢,下麵是一個 Spring 項目中 ip2region 幫助類來實現ip地址解析

/**
 * ip2region工具類
 */
@Slf4j
@Component
public class Ip2region {

    private Searcher searcher = null;

    @Value("${ip2region.path:}")
    private String ip2regionPath = "";

    @PostConstruct
    private void init() {
        // 1、從 dbPath 載入整個 xdb 到記憶體。
        String dbPath = ip2regionPath;

        // 1、從 dbPath 載入整個 xdb 到記憶體。
        byte[] cBuff;
        try {
            cBuff = Searcher.loadContentFromFile(dbPath);
            searcher = Searcher.newWithBuffer(cBuff);
        } catch (Exception e) {
            log.error("failed to create content cached searcher: {}", e.getMessage(), e);
        }
    }

    public IpInfoBean getIpInfo(String ip) {
        if (StringUtils.isBlank(ip)) {
            return null;
        }

        // 3、查詢
        try {
            long sTime = System.nanoTime();
            // 國家|區域|省份|城市|ISP
            String region = searcher.search(ip);
            long cost = TimeUnit.NANOSECONDS.toMicros((long) (System.nanoTime() - sTime));
            log.info("{region: {}, ioCount: {}, took: {} μs}", region, searcher.getIOCount(), cost);
            if (StringUtils.isNotBlank(region)) {
                String[] split = region.split("\|");
                IpInfoBean ipInfo = new IpInfoBean();
                ipInfo.setIp(ip);
                if (!"".equals(split[0])) {
                    ipInfo.setCountry(split[0]);
                }
                if (!"".equals(split[2])) {
                    ipInfo.setProvince(split[2]);
                }
                if (!"".equals(split[3])) {
                    ipInfo.setCity(split[3]);
                }
                if (!"".equals(split[4])) {
                    ipInfo.setIsp(split[4]);
                }
                return ipInfo;
            }
        } catch (Exception e) {
            log.error("failed to search({}): {}", ip, e);
            return null;
        }

        // 4、關閉資源 - 該 searcher 對象可以安全用於併發,等整個服務關閉的時候再關閉 searcher
        // searcher.close();

        // 備註:併發使用,用整個 xdb 數據緩存創建的查詢對象可以安全的用於併發,也就是你可以把這個 searcher 對象做成全局對象去跨線程訪問。
        return null;
    }
}

要註意得就是 ip2region v2.0 版本使用的xdb文件不建議放在項目 resources 下一起打包,存在編碼格式問題,建議通過指定路徑載入得方式單獨放在伺服器目錄下

五. 優雅得Springboot + mybatis配置多數據源方式

Springboot + mybatis 得項目中一般通過 @MapperScan 註解配置 dao 層包目錄,來實現 dao 層增強,其實項目中配置一個@MapperScan 是指定一個數據源,配置兩個@MapperScan就可以指定兩個數據源,通過不同得 dao 層包目錄區分,來實現不同數據源得訪問隔離。

比如下麵代碼中,com.xxx.dao.master 目錄下為主數據源 dao 文件,com.xxx.dao.slave 為從數據源 dao 文件,這個方式比網上得基於 aop 加註解得方式更加簡潔好用,也沒有單個方法中使用不同數據源切換得問題,因此推薦這種寫法

/**
 * 主數據源
 */
@Slf4j
@Configuration
@MapperScan(basePackages = {"com.xxx.dao.master"},
        sqlSessionFactoryRef = "MasterSqlSessionFactory")
public class MasterDataSourceConfig {

    @Bean(name = "MasterDataSource")
    @Qualifier("MasterDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.master")
    public DataSource clickHouseDataSource() {
        return DruidDataSourceBuilder.create().build();
    }

    @Bean(name = "MasterSqlSessionFactory")
    public SqlSessionFactory getSqlSessionFactory(@Qualifier("MasterDataSource") DataSource dataSource) throws Exception {
        MybatisSqlSessionFactoryBean sessionFactoryBean = new MybatisSqlSessionFactoryBean();
        sessionFactoryBean.setDataSource(dataSource);
        sessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
                .getResources("classpath*:mapper/master/*.xml"));
        log.info("------------------------------------------MasterDataSource 配置成功");
        return sessionFactoryBean.getObject();
    }
}

/**
 * 從數據源
 */
@Slf4j
@Configuration
@MapperScan(basePackages = {"com.xxx.dao.slave"},
        sqlSessionFactoryRef = "SlaveSqlSessionFactory")
public class MasterDataSourceConfig {

    @Bean(name = "SlaveDataSource")
    @Qualifier("SlaveDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.slave")
    public DataSource clickHouseDataSource() {
        return DruidDataSourceBuilder.create().build();
    }

    @Bean(name = "SlaveSqlSessionFactory")
    public SqlSessionFactory getSqlSessionFactory(@Qualifier("SlaveDataSource") DataSource dataSource) throws Exception {
        MybatisSqlSessionFactoryBean sessionFactoryBean = new MybatisSqlSessionFactoryBean();
        sessionFactoryBean.setDataSource(dataSource);
        sessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
                .getResources("classpath*:mapper/slave/*.xml"));
        log.info("------------------------------------------SlaveDataSource 配置成功");
        return sessionFactoryBean.getObject();
    }
}

數據源yml配置

spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driverClassName: com.mysql.cj.jdbc.Driver
    # 主庫數據源
    master:
      url: jdbc:mysql://localhost:3306/db1?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8
      username: root
      password:
    slave:
      url: jdbc:mysql://localhost:3306/db2?useUnicode=true&characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&useSSL=true&serverTimezone=GMT%2B8
      username: root
      password:

博主剛開始編碼一、兩年得時候一個項目中遇到了多數據源使用得問題,那時候題主便在網上搜索Spring 多數據源得帖子,大多數都是基於Spring提供得AbstractRoutingDataSource + AOP + 註解 來做動態切換,包括現在流行得 Mybatis plus 官方得多數據源解決方案也是這種做法,這種做法解決了博主當時得多數據源使用問題,後來加了一個需求,在一個定時任務中,查詢兩個數據源得數據,才發現動態切換在單個方法中不好用了,最後使用得原生jdbc數據源解決。多年後,博主在另一家公司得項目中又遇到了多數據源問題,但是這次博主在網上搜索得是Mybatis 多數據源,才發現了這個優雅得解決方案,進而推薦給大家

六. Spring Security項目中,使用MDC實現介面請求調用追蹤,以及用戶ID記錄

MDC介紹

MDC(Mapped Diagnostic Context,映射調試上下文)是 log4j 、logback及log4j2 提供的一種方便在多線程條件下記錄日誌的功能。MDC 可以看成是一個與當前線程綁定的哈希表,可以往其中添加鍵值對。MDC 中包含的內容可以被同一線程中執行的代碼所訪問。當前線程的子線程會繼承其父線程中的 MDC 的內容。當需要記錄日誌時,只需要從 MDC 中獲取所需的信息即可。

雖然MDC能夠方便得實現介面請求調用追蹤功能,但是它在子線程中會丟失父線程中添加得鍵值對信息,解決方法是通過父線程中調用線程池前調用 MDC.getCopyOfContextMap() ,然後在子線程中第一個調用 MDC.setConextMap() 獲取鍵值對信息,完整實現代碼如下:

/**
 * 自定義Spring線程池,解決子線程丟失reqest_id問題
 */
public class ThreadPoolExecutorMdcWrapper extends ThreadPoolTaskExecutor {

    @Override
    public void execute(Runnable task) {
        super.execute(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }

    @Override
    public <T> Future<T> submit(Callable<T> task) {
        return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }

    @Override
    public Future<?> submit(Runnable task) {
        return super.submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }
}

/**
 * MDC幫助類,添加reqest_id
 */
public class ThreadMdcUtil {


    public static final String REQUEST_ID = "request_id";

    /**
     * 設置請求唯一ID
     */
    public static void setTraceIdIfAbsent() {
        if (MDC.get(REQUEST_ID) == null) {
            MDC.put(REQUEST_ID, IdUtil.getUid());
        }
    }

    /**
     * 存在userId則添加到REQUEST_ID中
     * @param userId
     */
    public static void setUserId(String userId) {
        String s = MDC.get(REQUEST_ID);
        if (s != null) {
            MDC.put(REQUEST_ID, s + "_" + userId);
        }
    }

    public static void removeTraceId() {
        MDC.remove(REQUEST_ID);
    }

    public static <T> Callable<T> wrap(final Callable<T> callable, final Map<String, String> context) {
        return () -> {
            if (context == null) {
                MDC.clear();
            } else {
                MDC.setContextMap(context);
            }
            setTraceIdIfAbsent();
            try {
                return callable.call();
            } finally {
                MDC.clear();
            }
        };
    }

    public static Runnable wrap(final Runnable runnable, final Map<String, String> context) {
        return () -> {
            if (context == null) {
                MDC.clear();
            } else {
                MDC.setContextMap(context);
            }
            // 設置traceId
            setTraceIdIfAbsent();
            try {
                runnable.run();
            } finally {
                MDC.clear();
            }
        };
    }
}

Spring Security 中添加 token 過濾器

/**
 * token過濾器 驗證token有效性
 *
 * @author ruoyi
 */
@Slf4j
@Component
public class JwtAuthenticationTokenFilter extends OncePerRequestFilter {

    @Autowired
    private TokenService tokenService;


    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
            throws ServletException, IOException {
        try {
            // 入口傳入請求ID
            ThreadMdcUtil.setTraceIdIfAbsent();
            LoginUserDetail loginUser = tokenService.getLoginUser(request);
            if (Objects.nonNull(loginUser) && Objects.isNull(SecurityContextHolder.getContext().getAuthentication())) {
                // 記錄userId
                ThreadMdcUtil.setUserId(String.valueOf(loginUser.getMember().getId()));
                tokenService.verifyToken(loginUser);
                UsernamePasswordAuthenticationToken authenticationToken = new UsernamePasswordAuthenticationToken(loginUser, null, loginUser.getAuthorities());
                authenticationToken.setDetails(new WebAuthenticationDetailsSource().buildDetails(request));
                SecurityContextHolder.getContext().setAuthentication(authenticationToken);
            }
            chain.doFilter(request, response);
        } finally {
            // 出口移除請求ID
            ThreadMdcUtil.removeTraceId();
        }
    }

}

最後在 logback.xml 中添加 %X{request_id}

<property name="pattern"
          value="%d{yyyy-MM-dd HH:mm:ss.SSS} [%X{request_id}] [%thread] [%-5level] %logger{36}:%L %M - %msg%n"/>

日誌列印效果如下:

2022-11-27 21:29:48.008 [86c76336100c414dbe9217aeb099ccd5_12] [http-nio-82-exec-2] [INFO ] c.w.m.a.s.impl.IHomeServiceImpl:56 getHomeIndexDataCompletableFuture - getHomeIndexDataCompletableFuture:[email protected][code=200,msg=操作成功,map={bannerList=[{"createTime":"2020-06-26 19:56:03","delFlag":false,"id":14,"imgUrl":"https://m.360buyimg.com/mobilecms/s700x280_jfs/t1/117335/39/13837/263099/5f291a83E8ba761d0/5c0460445cb28248.jpg!cr_1125x449_0_166!q70.jpg.dpg","jumpUrl":"http://82.157.141.70/mall/#/detail/1155015","sort":0,"status":0,"title":"hh2","updateTime":"2022-06-19 09:16:46"},{"createTime":"2020-06-26 19:56:03","delFlag":false,"id":15,"imgUrl":"https://m.360buyimg.com/mobilecms/s700x280_jfs/t1/202096/26/11652/265782/616acb67E4fcdc9ac/8d7cdfbb6c934e67.jpg!cr_1125x449_0_166!q70.jpg.dpg","jumpUrl":"#/detail/1155015","sort":0,"status":0,"title":"hh","updateTime":"2022-06-19 09:04:58"}], newGoodsList=[{"actualSales":0,"brandId":0,"brief":"酥脆奶香,甜酸回味","categoryId":1008015,"counterPrice":56.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1116011","id":1116011,"isHot":true,"isNew":true,"isOnSale":true,"keywords":"","name":"蔓越莓曲奇 200克","picUrl":"http://yanxuan.nosdn.127.net/767b370d07f3973500db54900bcbd2a7.png","retailPrice":36.00,"shareUrl":"","sort":5,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"粉彩色澤,記錄生活","categoryId":1012003,"counterPrice":49.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1127047","id":1127047,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"趣味粉彩系列筆記本","picUrl":"http://yanxuan.nosdn.127.net/6c03ca93d8fe404faa266ea86f3f1e43.png","retailPrice":29.00,"shareUrl":"","sort":2,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"慢回彈海綿,時尚設計。","categoryId":1008002,"counterPrice":66.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1134030","id":1134030,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"簡約知性記憶棉坐墊","picUrl":"http://yanxuan.nosdn.127.net/aa49dfe878becf768eddc4c1636643a6.png","retailPrice":46.00,"shareUrl":"","sort":12,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"慢回彈海綿的呵護,萌趣添彩。","categoryId":1008002,"counterPrice":69.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1134032","id":1134032,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"趣味粉彩系列記憶棉坐墊","picUrl":"http://yanxuan.nosdn.127.net/8b30eeb17c831eba08b97bdcb4c46a8e.png","retailPrice":49.00,"shareUrl":"","sort":13,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"100%桑蠶絲,絲滑潤膚","categoryId":1008009,"counterPrice":2619.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1135002","id":1135002,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"宮廷奢華真絲四件套","picUrl":"http://yanxuan.nosdn.127.net/45548f26cfd0c7c41e0afc3709d48286.png","retailPrice":2599.00,"shareUrl":"","sort":1,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"自由海軍領探索未來夢","categoryId":1020003,"counterPrice":89.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1135072","id":1135072,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"經典海魂紋水手裙(嬰童)","picUrl":"http://yanxuan.nosdn.127.net/43e57d4208cdc78ac9c088f9b3e798f5.png","retailPrice":69.00,"shareUrl":"","sort":3,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"經典海魂紋自由海軍領","categoryId":1020003,"counterPrice":89.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1135073","id":1135073,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"海魂紋哈衣水手服(嬰童)","picUrl":"http://yanxuan.nosdn.127.net/53052b04ae001d289c040e09ea92231c.png","retailPrice":69.00,"shareUrl":"","sort":4,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":5,"brandId":0,"brief":"差旅好伴侶","categoryId":1032000,"counterPrice":119.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1152031","id":1152031,"isHot":true,"isNew":true,"isOnSale":true,"keywords":"","name":"魔獸世界-伊利丹頸枕眼罩套裝","picUrl":"http://yanxuan.nosdn.127.net/fd6e78a397bd9e9804116a36f0270b0a.png","retailPrice":99.00,"shareUrl":"","sort":4,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":5,"brandId":0,"brief":"桌面整理神器","categoryId":1032000,"counterPrice":519.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1152095","id":1152095,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"魔獸世界 聯盟·暴風城 堡壘收納盒","picUrl":"http://yanxuan.nosdn.127.net/c86b49f635fa141decebabbd0966a6ef.png","retailPrice":499.00,"shareUrl":"","sort":6,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":0,"brandId":0,"brief":"3重透氣,清爽柔滑","categoryId":1008009,"counterPrice":479.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1152161","id":1152161,"isHot":false,"isNew":true,"isOnSale":true,"keywords":"","name":"竹語絲麻印花四件套","picUrl":"http://yanxuan.nosdn.127.net/977401e75113f7c8334c4fb5b4bf6215.png","retailPrice":459.00,"shareUrl":"","sort":6,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10}], categoryList=[{"createTime":"2020-12-08 23:09:12","delFlag":false,"iconUrl":"http://cdn.wayn.xin/9fc3c52571aa38a1466f114c2dc892fc.png","id":2,"jumpType":0,"name":"大牌手機","picUrl":"http://cdn.wayn.xin/2545dd00ca4575759024af2811949a9d.jpg","sort":1,"status":0,"updateTime":"2020-12-12 19:26:48","valueId":5,"valueUrl":"http://baidu.com"},{"createTime":"2020-12-06 13:27:54","delFlag":false,"iconUrl":"http://82.157.141.70/upload/2022/02/21/a23fa32c8f4004a8c9fbbb1784462163.jpg","id":1,"jumpType":0,"name":"滋補保健2","picUrl":"http://cdn.wayn.xin/d4de7172eb7ae4178ae4dafd6a973d8f.jpg","sort":2,"status":0,"updateTime":"2022-06-19 09:17:20","valueId":2},{"createTime":"2020-12-08 23:26:15","delFlag":false,"iconUrl":"http://cdn.wayn.xin/6bc0f8a131d2d16b8fc2004d4aa4860c.png","id":3,"jumpType":1,"name":"不鏽鋼鍋","picUrl":"http://cdn.wayn.xin/314d87257f7a2ff03d5f4c5183797912.jpg","sort":2,"status":0,"updateTime":"2020-12-12 19:27:24","valueId":1036000},{"createTime":"2020-12-12 19:28:08","delFlag":false,"iconUrl":"http://cdn.wayn.xin/5a90531d901529967885279d7dc826e1.png","id":14,"jumpType":0,"name":"進口牛奶","picUrl":"http://cdn.wayn.xin/0b1f6ab63d5e222c52c83a2d0581e44c.jpg","sort":3,"status":0,"valueId":5},{"createTime":"2020-12-12 19:28:33","delFlag":false,"iconUrl":"http://cdn.wayn.xin/33530951827ca7e59940d51cda537d84.png","id":15,"jumpType":0,"name":"量販囤貨","picUrl":"http://cdn.wayn.xin/bb6daee3b3e51c3008db97585249f513.jpg","sort":4,"status":0,"valueId":2},{"createTime":"2020-12-12 19:28:50","delFlag":false,"iconUrl":"http://cdn.wayn.xin/7d337f25111b263b29d5d12589015c46.png","id":16,"jumpType":0,"name":"清潔用品","picUrl":"http://cdn.wayn.xin/be8995bda39d03b17349b8ec0dcab3d5.jpg","sort":5,"status":0,"valueId":2},{"createTime":"2020-12-12 19:29:10","delFlag":false,"iconUrl":"http://cdn.wayn.xin/2e632ec0173bb477dcdb601495e0412a.png","id":17,"jumpType":0,"name":"洗護用品","picUrl":"http://cdn.wayn.xin/53fb88c9d1245caa882aa3fc29187d0b.jpg","sort":6,"status":0,"valueId":4},{"createTime":"2020-12-12 19:29:28","delFlag":false,"iconUrl":"http://cdn.wayn.xin/942323c0e74677cf2aa15f09a1e63bca.png","id":18,"jumpType":0,"name":"日用百貨","picUrl":"http://cdn.wayn.xin/8587f91db2edcb43e57da9835cc7ec76.jpg","sort":7,"status":0,"valueId":2},{"createTime":"2020-12-12 19:29:46","delFlag":false,"iconUrl":"http://cdn.wayn.xin/18d9d860ba9b8b28522e050f11a8a8e0.png","id":19,"jumpType":0,"name":"明星乳膠","picUrl":"http://cdn.wayn.xin/65273c7fb2273e90958e92626248a90a.jpg","sort":8,"status":0,"valueId":6},{"createTime":"2020-12-12 19:30:15","delFlag":false,"iconUrl":"http://cdn.wayn.xin/7c790577afda91eebc3c95586e190957.png","id":20,"jumpType":0,"name":"口碑好物","picUrl":"http://cdn.wayn.xin/210011b35be4ceee39e6a466b40b8e22.jpg","sort":9,"status":0,"updateTime":"2021-04-01 20:13:08","valueId":5}], expire_time=1669549170235, hotGoodsList=[{"actualSales":1,"brandId":1001045,"brief":"一級桑蠶絲,吸濕透氣柔軟","categoryId":1036000,"counterPrice":719.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1006013","id":1006013,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"雙宮繭桑蠶絲被 空調被","picUrl":"http://yanxuan.nosdn.127.net/583812520c68ca7995b6fac4c67ae2c7.png","retailPrice":699.00,"shareUrl":"","sort":7,"unit":"件","updateTime":"2021-08-08 11:19:36","virtualSales":10},{"actualSales":1,"brandId":1001045,"brief":"雙層子母被,四季皆可使用","categoryId":1008008,"counterPrice":14199.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1006014","id":1006014,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"雙宮繭桑蠶絲被 子母被","picUrl":"http://yanxuan.nosdn.127.net/2b537159f0f789034bf8c4b339c43750.png","retailPrice":1399.00,"shareUrl":"","sort":15,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":6,"brandId":1001000,"brief":"加大加厚,雙色精彩","categoryId":1036000,"counterPrice":219.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1011004","id":1011004,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"色織精梳AB紗格紋空調被","picUrl":"http://yanxuan.nosdn.127.net/0984c9388a2c3fd2335779da904be393.png","retailPrice":199.00,"shareUrl":"","sort":2,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":6,"brandId":0,"brief":"共用親密2人時光","categoryId":1008008,"counterPrice":219.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1019002","id":1019002,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"升級款護頸雙人記憶枕","picUrl":"http://yanxuan.nosdn.127.net/0118039f7cda342651595d994ed09567.png","retailPrice":199.00,"shareUrl":"","sort":10,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":6,"brandId":0,"brief":"健康保護枕","categoryId":1008008,"counterPrice":119.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1019006","id":1019006,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"植物填充護頸夜交藤枕","picUrl":"http://yanxuan.nosdn.127.net/60c3707837c97a21715ecc3986a744ce.png","retailPrice":99.00,"shareUrl":"","sort":7,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":6,"brandId":0,"brief":"厚實舒適","categoryId":1008001,"counterPrice":59.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1021000","id":1021000,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"被","name":"埃及進口長絨棉毛巾","picUrl":"http://yanxuan.nosdn.127.net/7191f2599c7fe44ed4cff7a76e853154.png","retailPrice":39.00,"shareUrl":"","sort":7,"unit":"條","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":6,"brandId":1001020,"brief":"浪漫毛線繡球,簡約而不簡單","categoryId":1008009,"counterPrice":319.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1022000","id":1022000,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"意式毛線繡球四件套","picUrl":"http://yanxuan.nosdn.127.net/5350e35e6f22165f38928f3c2c52ac57.png","retailPrice":299.00,"shareUrl":"","sort":18,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":32,"brandId":1001000,"brief":"柔軟紗布,嬰童可用","categoryId":1036000,"counterPrice":269.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1027004","id":1027004,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"色織六層紗布夏涼被","picUrl":"http://yanxuan.nosdn.127.net/6252f53aaf36c072b6678f3d8c635132.png","retailPrice":249.00,"shareUrl":"","sort":3,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":32,"brandId":0,"brief":"原生苦蕎,健康護頸","categoryId":1008008,"counterPrice":119.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1036002","id":1036002,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"高山苦蕎麥枕","picUrl":"http://yanxuan.nosdn.127.net/ffd7efe9d5225dff9f36d5110b027caa.png","retailPrice":99.00,"shareUrl":"","sort":5,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10},{"actualSales":32,"brandId":0,"brief":"5cm記憶綿的親密包裹","categoryId":1008008,"counterPrice":619.00,"createTime":"2018-02-01 00:00:00","delFlag":false,"goodsSn":"1037011","id":1037011,"isHot":true,"isNew":false,"isOnSale":true,"keywords":"","name":"安睡慢回彈記憶綿床墊","picUrl":"http://yanxuan.nosdn.127.net/a03ea6f4509439acdafcb7ceba1debe0.png","retailPrice":599.00,"shareUrl":"","sort":22,"unit":"件","updateTime":"2018-02-01 00:00:00","virtualSales":10}]}]
2022-11-27 21:29:48.336 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage_mpCount:137 debug - ==>  Preparing: SELECT COUNT(*) AS total FROM shop_goods WHERE del_flag = 0 AND is_on_sale = 1
2022-11-27 21:29:48.387 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage_mpCount:137 debug - ==> Parameters: 
2022-11-27 21:29:48.426 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage_mpCount:137 debug - <==      Total: 1
2022-11-27 21:29:48.430 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage:137 debug - ==>  Preparing: select id, goods_sn, name, pic_url, counter_price, retail_price, actual_sales, virtual_sales from shop_goods WHERE del_flag = 0 and is_on_sale = 1 order by create_time desc LIMIT ?
2022-11-27 21:29:48.452 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage:137 debug - ==> Parameters: 6(Long)
2022-11-27 21:29:48.476 [9d919fb6d33c4652ba28ff87ae210809_12] [http-nio-82-exec-3] [DEBUG] c.w.c.c.m.s.G.selectGoodsListPage:137 debug - <==      Total: 6

最後分析上訴日誌:通過86c76336100c414dbe9217aeb099ccd5實現介面調用追蹤,通過12用戶ID,實現用戶調用追蹤

七. alibaba excel導出時自定義格式轉換優雅實現

官網介紹:EasyExcel 是一個基於Java的簡單、省記憶體的讀寫Excel的開源項目。在儘可能節約記憶體的情況下支持讀寫百M的Excel。

EasyExcelalibaba 出的一個基於 java poi 得excel通用處理類庫,他的優勢在於記憶體消耗。對比 easypoi 方案,EasyExcel 在記憶體消耗、知名度(大廠光環)上更出眾些。

博主在使用過程中發現導出excel,官網對自定義格式欄位提供了 converter 介面,但只簡單提供了CustomStringStringConverter 類代碼,達不到博主想要得優雅要求,如下:

public class CustomStringStringConverter implements Converter<String> {
    @Override
    public Class<?> supportJavaTypeKey() {
        return String.class;
    }

    @Override
    public CellDataTypeEnum supportExcelTypeKey() {
        return CellDataTypeEnum.STRING;
    }

    /**
     * 這裡讀的時候會調用
     *
     * @param context
     * @return
     */
    @Override
    public String convertToJavaData(ReadConverterContext<?> context) {
        return "自定義:" + context.getReadCellData().getStringValue();
    }

    /**
     * 這裡是寫的時候會調用 不用管
     *
     * @return
     */
    @Override
    public WriteCellData<?> convertToExcelData(WriteConverterContext<String> context) {
        return new WriteCellData<>(context.getValue());
    }

}

在以上代碼中,打個比方想要實現性別欄位得自定義格式轉換,就需要在convertToExcelData方法中,添加如下代碼

@Override
public WriteCellData<?> convertToExcelData(WriteConverterContext<String> context) {
    String value = context.getValue();
    if ("man".equals(value)) {
        return new WriteCellData<>("男");
    } else {
        return new WriteCellData<>("女");
    }
}

可以看到,非常得不優雅,對於這種類型欄位,博主習慣使用枚舉類來定義欄位所有類型,然後將枚舉類轉換為 map(value,desc) 結構,就可以優雅得實現這個自定義格式得需求

/**
 * 一、先定義int欄位抽象轉換類,實現通用轉換邏輯
 */
public abstract class AbstractIntConverter implements Converter<Integer> {
    abstract List<ConverterDTO> getArr();

    public WriteCellData<?> convertToExcelData(Integer value, ExcelContentProperty contentProperty, GlobalConfiguration globalConfiguration) {
        List<ConverterDTO> values = getArr();
        Map<Integer, String> map = values.stream().collect(toMap(ConverterDTO::getType, ConverterDTO::getDesc));
        String result = map.getOrDefault(value, "");
        return new WriteCellData<>(result);
    }

    static class ConverterDTO {
        private Integer type;
        private String desc;

        public Integer getType() {
            return type;
        }

        public void setType(Integer type) {
            this.type = type;
        }

        public String getDesc() {
            return desc;
        }

        public void setDesc(String desc) {
            this.desc = desc;
        }

        public ConverterDTO(Integer type, String desc) {
            this.type = type;
            this.desc = desc;
        }
    }
}

/**
 * 二、定義通用狀態欄位轉換類
 */
public class StatusConverter extends AbstractIntConverter {

    @Override
    List<ConverterDTO> getArr() {
        StatusEnum[] values = StatusEnum.values();
        return Arrays.stream(values).map(sexEnum -> new ConverterDTO(sexEnum.getType(), sexEnum.getDesc())).toList();
    }

    /**
     * 狀態枚舉
     */
    enum StatusEnum {
        MAN(0, "啟用"),
        WOMAN(1, "禁用");

        private Integer type;
        private String desc;

        StatusEnum(Integer type, String desc) {
            this.type = type;
            this.desc = desc;
        }
        public Integer getType() {
            return type;
        }
        public String getDesc() {
            return desc;
        }
    }
}

最後再導出 ExcelProperty 中甜膩加 StatusConverter ,就優雅得實現了自定義格式得需求

public class User extends BaseEntity {
    ...
    /**
     * 用戶狀態 0 啟用 1 禁用
     */
    @ExcelProperty(value = "用戶狀態", converter = StatusConverter.class)
    private Integer userStatus;
    ...

}

八. Springboot 預設redis客戶端lettuce經常連接超時解決方案

不知道大家有沒有遇到這種情況,線上項目使用 lettuce 客戶端,當操作 redis 得介面一段時間沒有調用後(比如30分鐘),再次調用 redis 操作後,就會遇到連接超時得問題,導致介面異常。博主直接給出分析過程:

  1. 通過wireshark抓包工具,發現項目中 redis 連接創建後,一段時間未傳輸數據後,客戶端發送 psh 包,未收到服務端 ack 包,觸發tcp得超時重傳機制,在重傳次數重試完後,最終客戶端主動關閉了連接。

到這裡我們就知道這個問題,主要原因在於服務端沒有回覆客戶端(比如tcp參數設置、防火牆主動關閉等,都是針對一段時間內沒有數據傳輸得tcp連接會做關閉處理),造成了客戶端得連接超時

面對這個問題有三種解決方案:

  • redis操作異常後進行重試,這篇文章有介紹 生產環境Redis連接,長時間無響應被伺服器斷開問題
  • 啟用一個心跳定時任務,定時訪問 redis,保持 redis 連接不被關閉,簡而言之,就是寫一個定時任務,定時調用 redisget 命令,進而保活 redis 連接
  • 基於Springboot 提供得 LettuceClientConfigurationBuilderCustomizer 自定義客戶端配置,博主這裡主要針對第三種自定義客戶端配置來講解一種優雅得方式

Springboot 項目中關於 lettuce 客戶端得自動配置是沒有啟用保活配置得,要啟用得話代碼如下:

/**
 * 自定義lettuce客戶端配置
 *
 * @return LettuceClientConfigurationBuilderCustomizer
 */
@Bean
public LettuceClientConfigurationBuilderCustomizer lettuceClientConfigurationBuilderCustomizer() {
    return clientConfigurationBuilder -> {
        LettuceClientConfiguration clientConfiguration = clientConfigurationBuilder.build();
        ClientOptions clientOptions = clientConfiguration.getClientOptions().orElseGet(ClientOptions::create);
        ClientOptions build = clientOptions.mutate().build();
        SocketOptions.KeepAliveOptions.Builder builder = build.getSocketOptions().getKeepAlive().mutate();
        // 保活配置
        builder.enable(true);
        builder.idle(Duration.ofSeconds(30));
        SocketOptions.Builder socketOptionsBuilder = clientOptions.getSocketOptions().mutate();
        SocketOptions.KeepAliveOptions keepAliveOptions = builder.build();
        socketOptionsBuilder.keepAlive(keepAliveOptions);
        SocketOptions socketOptions = socketOptionsBuilder.build();
        ClientOptions clientOptions1 = ClientOptions.builder().socketOptions(socketOptions).build();
        clientConfigurationBuilder.clientOptions(clientOptions1);
    };
}

添加 lettuce 客戶端的自定義配置,在 KeepAliveOptions 中啟用 enable ,這樣 lettuce 客戶端就會在tcp協議規範上啟用 keep alive 機制自動發送心跳包

九. redis客戶端lettuce啟用epoll

直接給 官網連接,配置很簡單,添加一個 netty-all 得依賴,lettuce 會自動檢測項目系統是否支持 epolllinux 系統支持),並且是否有netty-transport-native-epoll依賴( netty-all 包含 netty-transport-native-epoll ),都滿足得話就會自動啟用 epoll 事件迴圈,進一步提升系統性能

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
</dependency>

十. Springboot web項目優雅停機

web項目配置了優雅停機後,在重啟jar包,或者容器時可以防止正在活動得線程被突然停止( kill -9 無解,請不要使用這個參數殺線上進程,docker compose 項目儘量不要用 docker-compose down 命令關閉項目,使用 docker-compose rm -svf 可以觸發優雅停機),造成用戶請求失敗,在此期間允許完成現有請求但不允許新請求,配置如下:

server: shutdown: "graceful"

十一. nginx配置通用請求尾碼

先說下這個配置產生得前提,博主公司pc客戶項目是基於 electron 打包得網頁項目,每次項目大版本更新時,為了做好相容性,防止客戶端網頁緩存等,會使用一個新網頁地址,打個比方:

老網頁地址,v1.1.0 版本網頁訪問地址:http://api.dev.com/pageV110

新網頁地址,v1.2.0 版本網頁訪問地址:http://api.dev.com/pageV120

那麼項目得nginx配置則則需要新加一個 v1.2.0 得配置如下:

server {
   listen 80;
   server_name api.dev.com;
   client_max_body_size 10m;

   # 老網頁v1.1.0配置
   location ~ ^/pageV110 {
               alias  /home/wwwroot/api.dev.com/pageV110;
               index  index.html index.htm;
       }
       
   # 新網頁v1.2.0配置
   location ~ ^/pageV120 {
               alias  /home/wwwroot/api.dev.com/pageV120;
               index  index.html index.htm;
       }

}

那麼博主在每次項目發佈得時候就需要配合前端發版,配置一個新網頁,故產生了這個通用配置得需求,如下:

server {
   listen 80;
   server_name api.dev.com;
   client_max_body_size 10m;

   # 配置正則localtion
   location ~ ^/pageV(.*) {
               set $s $1; # 定義尾碼變數
               alias  /home/wwwroot/api.dev.com/pageV$s;
               index  index.html index.htm;
       }

}

nginx 配置文件語法中,location 語句可以使用正則表達式,定義 set $s $1 變數,實現了通用配置

十二. 關於開發人員的自我提升和突破

博主這裡主要總結了四點:

  1. 多和他人溝通,溝通能把複雜問題簡單化,有時候開發階段一個需求多問幾句,可以減少因為個人理解差異導致的需求不一致問題,進而減少開發時間
  2. 建立長短期目標,觀看技術視頻、書籍給自己充電,比如7天利用業餘時間看完一本電子書,三十天從零開始一個新項目等
  3. 善於總結,對於項目中的疑難bug,踩坑點要有記錄,防止下次遇到再掉坑裡
  4. 敢於嘗試、擔責,對項目、代碼里明確不合理的地方要敢於跟他人溝通,修改問題代碼,達到優化目的。對於自己造成的問題要承擔,不要推卸責任。對於線上問題要重視,優先解決線上問題。

您的分享是我們最大的動力!

-Advertisement-
Play Games
更多相關文章
  • hello,大家好呀,我是小樓。 前段時間不是在忙麽,忙的內容之一就是花了點時間重構了一個服務的健康檢查組件,目前已經慢慢在灰度線上,本文就來分享下這次重構之旅,也算作個總結吧。 背景 服務健康檢查簡介 服務健康檢查是應對分散式應用下某些服務節點不健康問題的一種解法。如下圖,消費者調用提供方集群,通 ...
  • 前言 這篇內容是從另一篇:UML建模、設計原則 中分離出來的,原本這個創建型設計模式是和其放在一起的 但是:把這篇創建型設計模式放在一起讓我賊彆扭,看起來賊不舒服,越看念頭越不通達,導致老衲躺在床上腦海中冒出來時都睡不著了 因此:最後實在受不了了,還是將其抽離出來 3、設計模式 分類: 註:使用設計 ...
  • Android ViewPager2 + Fragment 聯動 本篇主要介紹一下 ViewPager2 + Fragment , 上篇中簡單使用了ViewPager2 實現了一個圖片的滑動效果, 那圖片視圖可以滑動, ViewPager2也可以滑動 Fragment 概述 ViewPager2 官 ...
  • 〇、參考資料 1、Spring Boot 中文亂碼問題解決方案彙總 https://blog.51cto.com/u_15236724/5372824 2、spring boot讀取自定義配置properties文件★ https://www.yisu.com/zixun/366877.html 3 ...
  • 如何解決其中的可見性和有序性導致的問題,這也就引出來了今天的主角——Java 記憶體模型。 一、什麼是 Java 記憶體模型? 導致可見性的原因是緩存,導致有序性的原因是編譯優化,那解決可見性、有序性最直接的辦法就是禁用緩存和編譯優化,但這樣雖然解決了問題,但也導致帶來的性能優化都沒了。 因此,解決方案 ...
  • 背景 我們的springboot應用程式的持久層,是用jeecgboot框架生成的代碼。mybatisplus版本是3.1.2。 在一次對當前程式的sql性能優化時,我重寫了BaseMapper的selectPage方法。其中,為Wrapper<T>參數加上了id限制,以提高sql執行性能。 imp ...
  • 一.小結 1.不可變對象一旦創建,就不能改變。為防止用戶修改對象,可以定義不可變類。 2.實例變數和靜態變數的作用域是整個類,與變數在何處聲明無關。實例變數和靜態變數可以在類中的任意位置聲明。為保持一致,最好在類的起始位置聲明它們。 3.關鍵字this可用於表明調用對象。關鍵字this也可以用在構造 ...
  • 序言 各位好啊,我是會編程的蝸牛,作為java開發者,我們每天都要和開發工具打交道。我以前一開始入門java開發的時候,就是用的eclipse,雖然感覺有點繁瑣,但好在還能用。後來偶然間發現了IDEA,然後就漸漸被IDEA所吸引了,不過最近在做一些老項目的開發,大概是十幾年的那種技術,我發現用IDE ...
一周排行
    -Advertisement-
    Play Games
  • 1.部署歷史 猿友們好,作為初來實習的我,已經遭受社會的“毒打”,所以請容許我在下麵環節適當吐槽,3Q! 傳統部署 ​ 回顧以往在伺服器部署webapi項目(非獨立發佈),dotnet環境、守護進程兩個逃都逃不掉,正常情況下還得來個nginx代理。不僅僅這仨,可能牽扯到yum或npm。node等都要 ...
  • 隨著技術的進步,跨平臺開發已經成為了標配,在此大背景下,ASP.NET Core也應運而生。本文主要基於ASP.NET Core+Element+Sql Server開發一個校園圖書管理系統為例,簡述基於MVC三層架構開發的常見知識點,前一篇文章,已經簡單介紹瞭如何搭建開發框架,和登錄功能實現,本篇... ...
  • 這道題只要會自定義cmp恰當地進行排序,其他部分沒有什麼大問題。 上代碼: 1 #include<bits/stdc++.h> 2 using namespace std; 3 int n,s,h1,h2,cnt; 4 struct apple{ 5 int height,ns;//height為蘋 ...
  • 這篇文章主要描述RPC的路由策略,包括為什麼需要請求隔離,為什麼不在註冊中心中實現請求隔離以及不同粒度的路由策略。 ...
  • 簡介: 中介者模式,屬於行為型的設計模式。用一個中介對象來封裝一系列的對象交互。中介者是各對象不需要顯式地相互引用,從而使其耦合鬆散,而且可以獨立地改變他們之間的交互。 適用場景: 如果平行對象間的依賴複雜,可以使用中介者解耦。 優點: 符合迪米特法則,減少成員間的依賴。 缺點: 不適用於系統出現對 ...
  • 【前置內容】Spring 學習筆記全系列傳送門: Spring學習筆記 - 第一章 - IoC(控制反轉)、IoC容器、Bean的實例化與生命周期、DI(依賴註入) Spring學習筆記 - 第二章 - 註解開發、配置管理第三方Bean、註解管理第三方Bean、Spring 整合 MyBatis 和 ...
  • 簡介: 享元模式,屬於結構型的設計模式。運用共用技術有效地支持大量細粒度的對象。 適用場景: 具有相同抽象但是細節不同的場景中。 優點: 把公共的部分分離為抽象,細節依賴於抽象,符合依賴倒轉原則。 缺點: 增加複雜性。 代碼: //用戶類 class User { private $name; fu ...
  • 這次設計一個通用的多位元組SPI介面模塊,特點如下: 可以設置為1-128位元組的SPI通信模塊 可以修改CPOL、CPHA來進行不同的通信模式 可以設置輸出的時鐘 狀態轉移圖和思路與多位元組串口發送模塊一樣,這裡就不給出了,具體可看該隨筆。 一、模塊代碼 1、需要的模塊 通用8位SPI介面模塊 `tim ...
  • AOP-03 7.AOP-切入表達式 7.1切入表達式的具體使用 1.切入表達式的作用: 通過表達式的方式定義一個或多個具體的連接點。 2.語法細節: (1)切入表達式的語法格式: execution([許可權修飾符] [返回值類型] [簡單類名/全類名] [方法名]([參數列表]) 若目標類、介面與 ...
  • 測試一、虛繼承與繼承的區別 1.1 單個繼承,不帶虛函數 1>class B size(8): 1> + 1> 0 | + (base class A) 1> 0 | | _ia //4B 1> | + 1> 4 | _ib //4B 有兩個int類型數據成員,占8B,基類邏輯存在前面 1.2、單個 ...