时机一引入alibaba-starter-sentinel

如果使用了alibaba-starter-sentinel则不需要手动调用因为com.alibaba.cloud.sentinel.custom.SentinelAutoConfiguration#init在这里面执行了自动调用

@PostConstruct
    private void init() {
        if (StringUtils.isEmpty(System.getProperty(LogBase.LOG_DIR))
                && StringUtils.hasText(properties.getLog().getDir())) {
            System.setProperty(LogBase.LOG_DIR, properties.getLog().getDir());
        }
        if (StringUtils.isEmpty(System.getProperty(LogBase.LOG_NAME_USE_PID))
                && properties.getLog().isSwitchPid()) {
            System.setProperty(LogBase.LOG_NAME_USE_PID,
                    String.valueOf(properties.getLog().isSwitchPid()));
        }
        if (StringUtils.isEmpty(System.getProperty(SentinelConfig.APP_NAME_PROP_KEY))
                && StringUtils.hasText(projectName)) {
            System.setProperty(SentinelConfig.APP_NAME_PROP_KEY, projectName);
        }
        if (StringUtils.isEmpty(System.getProperty(TransportConfig.SERVER_PORT))
                && StringUtils.hasText(properties.getTransport().getPort())) {
            System.setProperty(TransportConfig.SERVER_PORT,
                    properties.getTransport().getPort());
        }
        if (StringUtils.isEmpty(System.getProperty(TransportConfig.CONSOLE_SERVER))
                && StringUtils.hasText(properties.getTransport().getDashboard())) {
            System.setProperty(TransportConfig.CONSOLE_SERVER,
                    properties.getTransport().getDashboard());
        }
        if (StringUtils.isEmpty(System.getProperty(TransportConfig.HEARTBEAT_INTERVAL_MS))
                && StringUtils
                        .hasText(properties.getTransport().getHeartbeatIntervalMs())) {
            System.setProperty(TransportConfig.HEARTBEAT_INTERVAL_MS,
                    properties.getTransport().getHeartbeatIntervalMs());
        }
        if (StringUtils.isEmpty(System.getProperty(TransportConfig.HEARTBEAT_CLIENT_IP))
                && StringUtils.hasText(properties.getTransport().getClientIp())) {
            System.setProperty(TransportConfig.HEARTBEAT_CLIENT_IP,
                    properties.getTransport().getClientIp());
        }
        if (StringUtils.isEmpty(System.getProperty(SentinelConfig.CHARSET))
                && StringUtils.hasText(properties.getMetric().getCharset())) {
            System.setProperty(SentinelConfig.CHARSET,
                    properties.getMetric().getCharset());
        }
        if (StringUtils
                .isEmpty(System.getProperty(SentinelConfig.SINGLE_METRIC_FILE_SIZE))
                && StringUtils.hasText(properties.getMetric().getFileSingleSize())) {
            System.setProperty(SentinelConfig.SINGLE_METRIC_FILE_SIZE,
                    properties.getMetric().getFileSingleSize());
        }
        if (StringUtils
                .isEmpty(System.getProperty(SentinelConfig.TOTAL_METRIC_FILE_COUNT))
                && StringUtils.hasText(properties.getMetric().getFileTotalCount())) {
            System.setProperty(SentinelConfig.TOTAL_METRIC_FILE_COUNT,
                    properties.getMetric().getFileTotalCount());
        }
        if (StringUtils.isEmpty(System.getProperty(SentinelConfig.COLD_FACTOR))
                && StringUtils.hasText(properties.getFlow().getColdFactor())) {
            System.setProperty(SentinelConfig.COLD_FACTOR,
                    properties.getFlow().getColdFactor());
        }
        if (StringUtils.hasText(properties.getBlockPage())) {
            setConfig(BLOCK_PAGE_URL_CONF_KEY, properties.getBlockPage());
        }

        // earlier initialize
        if (properties.isEager()) {
            InitExecutor.doInit();
        }

    }

时机二调用SphU.entry时

    // 1.5.0 版本开始可以直接利用 try-with-resources 特性 自动回收调用  entry.exit() 配合注解使用 @SentinelResource("HelloWorld")
                        try (Entry entry = SphU.entry(
                            "HelloWorld",
                            EntryType.IN)) {
                            // 被保护的逻辑
                            System.out.println(Thread.currentThread().getId() + "hello world" + (++i));

                        } catch (BlockException ex) {
                            i++;


                        }

com.alibaba.csp.sentinel.SphU#entry(java.lang.String, com.alibaba.csp.sentinel.EntryType)

 public static Entry entry(String name, EntryType trafficType) throws BlockException {
        return Env.sph.entry(name, trafficType, 1, OBJECTS0);
    }

类加载初始化

public class Env {

    public static final Sph sph = new CtSph();

    static {
        // If init fails, the process will exit.
        InitExecutor.doInit();
    }

}