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原因

在使用hystrix-dashboard面板的时候，然后我们然后显示错误“Unable to connect to Command Metric Stream”

分析

出现这个问题，首先我们需要检查一下，我们所依赖的jar是否有问题，需要依赖


其次是看启动项是否添加注解：@EnableHystrixDashboard，然后上网查了一下，

网上说

：

我们看到hytrix-dashboard上需要的接口是下面：



但是我们看到启动的console日志中打印出的是如下：



所以我们首先的解决方案，是把前面的”/application”去掉，需要在 .yml文件中配置上 ，然后上网查了一下，需要在 .yml文件中配置上

但是因为我用到的版本是“Greenwich.SR2”，是不支持的，所以这个方法也不能用了，然后终于在不懈努力下，然后解决方案；

解决方案

如果我们的SpringBoot是2.0以后版本，然后需要添加 ServletRegistrationBean 因为springboot的默认路径不是 “/hystrix.stream”。然后在项目中加上下面的配置就可以了；

@Bean
    public ServletRegistrationBean getServlet() {
        HystrixMetricsStreamServlet streamServlet = new HystrixMetricsStreamServlet();
        ServletRegistrationBean registrationBean = new ServletRegistrationBean(streamServlet);
        registrationBean.setLoadOnStartup(1);
        registrationBean.addUrlMappings("/hystrix.stream");
        registrationBean.setName("HystrixMetricsStreamServlet");
        return registrationBean;
    }

然后再重启服务，发送请求后，就可以显示下面的界面了。

然后我们可以看一下源码，在HystrixStreamEndpoint 从中可以看到 new EndpointServlet(HystrixMetricsStreamServlet.class）

package org.springframework.cloud.netflix.hystrix;

import com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsStreamServlet;
import java.util.Map;
import java.util.function.Supplier;
import org.springframework.boot.actuate.endpoint.web.EndpointServlet;
import org.springframework.boot.actuate.endpoint.web.annotation.ServletEndpoint;

@ServletEndpoint(
    id = "hystrix.stream"
)
public class HystrixStreamEndpoint implements Supplier<EndpointServlet> {
    private final Map<String, String> initParameters;

    public HystrixStreamEndpoint(Map<String, String> initParameters) {
        this.initParameters = initParameters;
    }

    public EndpointServlet get() {
        return (new EndpointServlet(HystrixMetricsStreamServlet.class)).withInitParameters(this.initParameters);
    }
}

然后，我们再查看 HystrixMetricsStreamServlet 这个类 在方法的注释中我们可以看到

有提示 “Adding the following to web.xml”。而在springboot中是采用bean的形式配置就可以解决问题了

package com.netflix.hystrix.contrib.metrics.eventstream;

import com.netflix.config.DynamicIntProperty;
import com.netflix.config.DynamicPropertyFactory;
import com.netflix.hystrix.contrib.sample.stream.HystrixSampleSseServlet;
import com.netflix.hystrix.metric.consumer.HystrixDashboardStream;
import com.netflix.hystrix.serial.SerialHystrixDashboardData;
import rx.Observable;
import rx.functions.Func1;

import java.util.concurrent.atomic.AtomicInteger;

/**
 * Streams Hystrix metrics in text/event-stream format.
 * <p>
 * Install by:
 * <p>
 * 1) Including hystrix-metrics-event-stream-*.jar in your classpath.
 * <p>
 * 2) Adding the following to web.xml:
 * <pre>{@code
 * <servlet>
 *  <description></description>
 *  <display-name>HystrixMetricsStreamServlet</display-name>
 *  <servlet-name>HystrixMetricsStreamServlet</servlet-name>
 *  <servlet-class>com.netflix.hystrix.contrib.metrics.eventstream.HystrixMetricsStreamServlet</servlet-class>
 * </servlet>
 * <servlet-mapping>
 *  <servlet-name>HystrixMetricsStreamServlet</servlet-name>
 *  <url-pattern>/hystrix.stream</url-pattern>
 * </servlet-mapping>
 * } </pre>
 */
public class HystrixMetricsStreamServlet extends HystrixSampleSseServlet {

    private static final long serialVersionUID = -7548505095303313237L;

    /* used to track number of connections and throttle */
    private static AtomicInteger concurrentConnections = new AtomicInteger(0);
    private static DynamicIntProperty maxConcurrentConnections =
            DynamicPropertyFactory.getInstance().getIntProperty("hystrix.config.stream.maxConcurrentConnections", 5);

    public HystrixMetricsStreamServlet() {
        this(HystrixDashboardStream.getInstance().observe(), DEFAULT_PAUSE_POLLER_THREAD_DELAY_IN_MS);
    }

    /* package-private */ HystrixMetricsStreamServlet(Observable<HystrixDashboardStream.DashboardData> sampleStream, int pausePollerThreadDelayInMs) {
        super(sampleStream.concatMap(new Func1<HystrixDashboardStream.DashboardData, Observable<String>>() {
            @Override
            public Observable<String> call(HystrixDashboardStream.DashboardData dashboardData) {
                return Observable.from(SerialHystrixDashboardData.toMultipleJsonStrings(dashboardData));
            }
        }), pausePollerThreadDelayInMs);
    }

    @Override
    protected int getMaxNumberConcurrentConnectionsAllowed() {
        return maxConcurrentConnections.get();
    }

    @Override
    protected int getNumberCurrentConnections() {
        return concurrentConnections.get();
    }

    @Override
    protected int incrementAndGetCurrentConcurrentConnections() {
        return concurrentConnections.incrementAndGet();
    }

    @Override
    protected void decrementCurrentConcurrentConnections() {
        concurrentConnections.decrementAndGet();
    }
}