一.jdk

//获取cpu核数
Runtime.getRuntime().availableProcessors()
//扩容为当前两倍
Cell[] rs = new Cell[n << 1];
//寻址
tab[i = (n - 1) & hash])
//返回Java虚拟机中的堆内存总量
long initialMemory = Runtime.getRuntime( ).totalMemory();
返回java虚拟机试图使用的最大堆内存量
long maxMemory = Runtime.getRuntime( ).maxMemory();
//输出响应内容
PrintWriter out = response.getWriter();
out.print(configInfoBase.getContent());
out.flush();
out.close();
//输出文件内容
File file = new File("test");
file .getChannel().transferTo(0L, fis.getChannel().size(), Channels.newChannel(response.getOutputStream()));
//判断是否是父子关系，结果是true，证明B可以转换成A
A.isAssignableFrom(B)

1.1创建单例的两种方式

①.双重检锁+volatile

public class VolatileTest {
    private static volatile VolatileTest sinleton;
    private VolatileTest(){
    }
    public static VolatileTest getInstance(){
        if (sinleton == null){
            synchronized (sinleton){
                if (sinleton == null) {
                    //1.分配内存空间 2.初始化对象 3.设置instance指向刚分配的内存地址
                    //如果不加volatile修饰可能会导致2和3顺序对调
                    sinleton = new VolatileTest();
                }
            }
        }
        return sinleton;
    }
}

②.静态内部类

public class VolatileTest {
   private VolatileTest(){
    }
    private static class VolatileHolder{
       private static final  VolatileTest INSTANCE = new VolatileTest();
    }
    public static VolatileTest getInstance(){
        return VolatileHolder.INSTANCE;
    }
}

1.2jdk的spi机制

在resources下META-INFO的services目录下定义接口的全路径接口名，在文件里定义实现类的全路径名，一个一行。
使用ServiceLoader.load(接口类)获取实现类

java方法以及框架总结 - 图1

1.3获取ip地址

public static String getRemoteIp(HttpServletRequest request) {
        String xForwardedFor = request.getHeader("X-Forwarded-For");
        if (!StringUtils.isBlank(xForwardedFor)) {
            return xForwardedFor.split(",")[0].trim();
        }
        String nginxHeader = request.getHeader("X-Real-IP");
        return StringUtils.isBlank(nginxHeader) ? request.getRemoteAddr() : nginxHeader;
    }

二.Nacos

字符串null转换为""
this.logName = Objects.toString(this.logName, "");

2.1获取ip信息

#获取ip信息
commons.util工具类
InetUtils inetUtils;
this.ip = this.inetUtils.findFirstNonLoopbackHostInfo().getIpAddress();
#网络接口名在大多数操作系统上（包括Windows、Linux和Unix）是以eth开头，后面是网络接口的索引号，从0开始。如本机安了三块网卡，那么网络接口名就依次是eth0、eth1和eth2.NetworkInterface对象的toString方法可以返回网络接口的名称、显示名和这个网络接口上绑字的所有IP地址等信息
NetworkInterface netInterface = NetworkInterface.getByName(this.networkInterface);

2.2创建观察者

#创建观察者
public class NacosWatch implements ApplicationEventPublisherAware, SmartLifecycle {
    private static final Logger log = LoggerFactory.getLogger(NacosWatch.class);
    private final NacosDiscoveryProperties properties;
    private final TaskScheduler taskScheduler;
    private final AtomicLong nacosWatchIndex;
    private final AtomicBoolean running;
    private ApplicationEventPublisher publisher;
    private ScheduledFuture<?> watchFuture;
    private Set<String> cacheServices;
    private HashMap<String, EventListener> subscribeListeners;
    public NacosWatch(NacosDiscoveryProperties properties) {
        this(properties, getTaskScheduler());
    }
    public NacosWatch(NacosDiscoveryProperties properties, TaskScheduler taskScheduler) {
        this.nacosWatchIndex = new AtomicLong(0L);
        this.running = new AtomicBoolean(false);
        this.cacheServices = new HashSet();
        this.subscribeListeners = new HashMap();
        this.properties = properties;
        this.taskScheduler = taskScheduler;
    }
    private static ThreadPoolTaskScheduler getTaskScheduler() {
        ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
        taskScheduler.initialize();
        return taskScheduler;
    }
}

2.3反射

#反射创建类
public static NamingService createNamingService(Properties properties) throws NacosException {
        try {
            Class<?> driverImplClass = Class.forName("com.alibaba.nacos.client.naming.NacosNamingService");
            Constructor constructor = driverImplClass.getConstructor(Properties.class);
            NamingService vendorImpl = (NamingService)constructor.newInstance(properties);
            return vendorImpl;
        } catch (Throwable var4) {
            throw new NacosException(-400, var4);
        }
    }

2.4心跳定时任务


/**
 * nacos心跳定时任务
 */
@Slf4j
public class BeatThread {
    private  ScheduledExecutorService executorService;
    public void task(){
        log.info("进入task中");
        executorService = new ScheduledThreadPoolExecutor(1, new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread thread = new Thread(r);
                thread.setDaemon(true);
                thread.setName(String.valueOf(new Random().nextInt(10)));
                return thread;
            }
        });
        executorService.schedule(new BeatTask(),1,TimeUnit.SECONDS);
    }
     class BeatTask implements Runnable {
        public BeatTask() {
        }
        @Override
        public void run() {
           log.info("进入线程任务中了");
            executorService.schedule(new BeatTask(),1,TimeUnit.SECONDS);
        }
    }
}

2.5故障转移

public String reqAPI(String api, Map<String, String> params, List<String> servers, String method) {
        params.put("namespaceId", this.getNamespaceId());
        if (CollectionUtils.isEmpty(servers) && StringUtils.isEmpty(this.nacosDomain)) {
            throw new IllegalArgumentException("no server available");
        } else {
            Exception exception = new Exception();
            if (servers != null && !servers.isEmpty()) {
                Random random = new Random(System.currentTimeMillis());
                int index = random.nextInt(servers.size());
                for(int i = 0; i < servers.size(); ++i) {
                    String server = (String)servers.get(index);
                    try {
                        return this.callServer(api, params, server, method);
                    } catch (NacosException var11) {
                        exception = var11;
                        LogUtils.NAMING_LOGGER.error("request {} failed.", server, var11);
                    } catch (Exception var12) {
                        exception = var12;
                        LogUtils.NAMING_LOGGER.error("request {} failed.", server, var12);
                    }
                    index = (index + 1) % servers.size();
                }
                throw new IllegalStateException("failed to req API:" + api + " after all servers(" + servers + ") tried: " + ((Exception)exception).getMessage());
            } else {
                int i = 0;
                while(i < 3) {
                    try {
                        return this.callServer(api, params, this.nacosDomain);
                    } catch (Exception var13) {
                        exception = var13;
                        LogUtils.NAMING_LOGGER.error("[NA] req api:" + api + " failed, server(" + this.nacosDomain, var13);
                        ++i;
                    }
                }
                throw new IllegalStateException("failed to req API:/api/" + api + " after all servers(" + servers + ") tried: " + ((Exception)exception).getMessage());
            }
        }
    }