分布式系统监控系统zipkin入门

zipkin为分布式链路调用监控系统，聚合各业务系统调用延迟数据，达到链路调用监控跟踪。

architecture

分布式系统监控系统zipkin入门
如图，在复杂的调用链路中假设存在一条调用链路响应缓慢，如何定位其中延迟高的服务呢？

日志：通过分析调用链路上的每个服务日志得到结果
zipkin：使用zipkin的web UI可以一眼看出延迟高的服务

分布式系统监控系统zipkin入门

如图所示，各业务系统在彼此调用时，将特定的跟踪消息传递至zipkin,zipkin在收集到跟踪信息后将其聚合处理、存储、展示等，用户可通过web UI方便
获得网络延迟、调用链路、系统依赖等等。

zipkin主要涉及四个组件 collector storage search web UI

Collector接收各service传输的数据
Cassandra作为Storage的一种，也可以是mysql等，默认存储在内存中，配置cassandra可以参考这里
Query负责查询Storage中存储的数据,提供简单的JSON API获取数据，主要提供给web UI使用
Web 提供简单的web界面

2.安装

执行如下命令下载jar包

wget -O zipkin.jar 'https://search.maven.org/remote_content?g=io.zipkin.java&a=zipkin-server&v=LATEST&c=exec'

其为一个spring boot 工程，直接运行jar

nohup java -jar zipkin.jar &

访问 http://ip:9411
分布式系统监控系统zipkin入门

概念：

使用zipkin涉及几个概念

Span:基本工作单元，一次链路调用(可以是RPC，DB等没有特定的限制)创建一个span，通过一个64位ID标识它，
span通过还有其他的数据，例如描述信息，时间戳，key-value对的(Annotation)tag信息，parent-id等,其中parent-id
可以表示span调用链路来源，通俗的理解span就是一次请求信息
Trace:类似于树结构的Span集合，表示一条调用链路，存在唯一标识
Annotation: 注解,用来记录请求特定事件相关信息(例如时间)，通常包含四个注解信息

cs - Client Start,表示客户端发起请求

sr - Server Receive,表示服务端收到请求

ss - Server Send,表示服务端完成处理，并将结果发送给客户端

cr - Client Received,表示客户端获取到服务端返回信息
BinaryAnnotation:提供一些额外信息，一般已key-value对出现

概念说完，来看下完整的调用链路
分布式系统监控系统zipkin入门

上图表示一请求链路，一条链路通过Trace Id唯一标识，Span标识发起的请求信息，各span通过parent id 关联起来，如图
分布式系统监控系统zipkin入门

整个链路的依赖关系如下:
分布式系统监控系统zipkin入门

完成链路调用的记录后，如何来计算调用的延迟呢，这就需要利用Annotation信息

分布式系统监控系统zipkin入门

sr-cs 得到请求发出延迟

ss-sr 得到服务端处理延迟

cr-cs 得到真个链路完成延迟

brave

作为各调用链路，只需要负责将指定格式的数据发送给zipkin即可，利用brave可快捷完成操作。

首先导入jar包pom.xml

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.3.6.RELEASE</version>
</parent>

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>io.zipkin.brave</groupId>
<artifactId>brave-core</artifactId>
<version>3.9.0</version>
</dependency>

<dependency>
<groupId>io.zipkin.brave</groupId>
<artifactId>brave-http</artifactId>
<version>3.9.0</version>
</dependency>
<dependency>
<groupId>io.zipkin.brave</groupId>
<artifactId>brave-spancollector-http</artifactId>
<version>3.9.0</version>
</dependency>
<dependency>
<groupId>io.zipkin.brave</groupId>
<artifactId>brave-web-servlet-filter</artifactId>
<version>3.9.0</version>
</dependency>
<dependency>
<groupId>io.zipkin.brave</groupId>
<artifactId>brave-okhttp</artifactId>
<version>3.9.0</version>
</dependency>

<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.13</version>
</dependency>
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.1</version>
</dependency>
</dependencies>

利用spring boot创建工程

Application.Java

package com.lkl.zipkin;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
/**
*
* Created by liaokailin on 16/7/27.
*/
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication app = new SpringApplication(Application.class);
app.run(args);
}
}

建立controller对外提供服务

HomeController.java

RestController
@RequestMapping("/")
public class HomeController {
@Autowired
private OkHttpClient client;
private Random random = new Random();
@RequestMapping("start")
public String start() throws InterruptedException, IOException {
int sleep= random.nextInt(100);
TimeUnit.MILLISECONDS.sleep(sleep);
Request request = new Request.Builder().url("http://localhost:9090/foo").get().build();
Response response = client.newCall(request).execute();
return " [service1 sleep " + sleep+" ms]" + response.body().toString();
}

HomeController中利用OkHttpClient调用发起http请求。在每次发起请求时则需要通过brave记录Span信息，并异步传递给zipkin
作为被调用方(服务端)也同样需要完成以上操作.

ZipkinConfig.java

package com.lkl.zipkin.config;
import com.github.kristofa.brave.Brave;
import com.github.kristofa.brave.EmptySpanCollectorMetricsHandler;
import com.github.kristofa.brave.SpanCollector;
import com.github.kristofa.brave.http.DefaultSpanNameProvider;
import com.github.kristofa.brave.http.HttpSpanCollector;
import com.github.kristofa.brave.okhttp.BraveOkHttpRequestResponseInterceptor;
import com.github.kristofa.brave.servlet.BraveServletFilter;
import okhttp3.OkHttpClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
/**
* Created by liaokailin on 16/7/27.
*/
@Configuration
public class ZipkinConfig {
@Autowired
private ZipkinProperties properties;
@Bean
public SpanCollector spanCollector() {
HttpSpanCollector.Config config = HttpSpanCollector.Config.builder().connectTimeout(properties.getConnectTimeout()).readTimeout(properties.getReadTimeout())
.compressionEnabled(properties.isCompressionEnabled()).flushInterval(properties.getFlushInterval()).build();
return HttpSpanCollector.create(properties.getUrl(), config, new EmptySpanCollectorMetricsHandler());
}
@Bean
public Brave brave(SpanCollector spanCollector){
Brave.Builder builder = new Brave.Builder(properties.getServiceName()); //指定state
builder.spanCollector(spanCollector);
builder.traceSampler(Sampler.ALWAYS_SAMPLE);
Brave brave = builder.build();
return brave;
}
@Bean
public BraveServletFilter braveServletFilter(Brave brave){
BraveServletFilter filter = new BraveServletFilter(brave.serverRequestInterceptor(),brave.serverResponseInterceptor(),new DefaultSpanNameProvider());
return filter;
}
@Bean
public OkHttpClient okHttpClient(Brave brave){
OkHttpClient client = new OkHttpClient.Builder()
.addInterceptor(new BraveOkHttpRequestResponseInterceptor(brave.clientRequestInterceptor(), brave.clientResponseInterceptor(), new DefaultSpanNameProvider()))
.build();
return client;
}
}

SpanCollector 配置收集器
Brave 各工具类的封装,其中builder.traceSampler(Sampler.ALWAYS_SAMPLE)设置采样比率，0-1之间的百分比
BraveServletFilter 作为拦截器，需要serverRequestInterceptor,serverResponseInterceptor 分别完成sr和ss操作
OkHttpClient 添加拦截器，需要clientRequestInterceptor,clientResponseInterceptor 分别完成cs和cr操作,该功能由
brave中的brave-okhttp模块提供，同样的道理如果需要记录数据库的延迟只要在数据库操作前后完成cs和cr即可，当然brave提供其封装。

以上还缺少一个配置信息ZipkinProperties.java

package com.lkl.zipkin.config;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;
/**
* Created by liaokailin on 16/7/28.
*/
@Configuration
@ConfigurationProperties(prefix = "com.zipkin")
public class ZipkinProperties {
private String serviceName;
private String url;
private int connectTimeout;
private int readTimeout;
private int flushInterval;
private boolean compressionEnabled;
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public int getConnectTimeout() {
return connectTimeout;
}
public void setConnectTimeout(int connectTimeout) {
this.connectTimeout = connectTimeout;
}
public int getReadTimeout() {
return readTimeout;
}
public void setReadTimeout(int readTimeout) {
this.readTimeout = readTimeout;
}
public int getFlushInterval() {
return flushInterval;
}
public void setFlushInterval(int flushInterval) {
this.flushInterval = flushInterval;
}
public boolean isCompressionEnabled() {
return compressionEnabled;
}
public void setCompressionEnabled(boolean compressionEnabled) {
this.compressionEnabled = compressionEnabled;
}
public String getServiceName() {
return serviceName;
}
public void setServiceName(String serviceName) {
this.serviceName = serviceName;
}
}

则可以在配置文件application.properties中配置相关信息

com.zipkin.serviceName=service1
com.zipkin.url=http://110.173.14.57:9411
com.zipkin.connectTimeout=6000
com.zipkin.readTimeout=6000
com.zipkin.flushInterval=1
com.zipkin.compressionEnabled=true
server.port=8080

那么其中的service1即完成，同样的道理，修改配置文件(调整com.zipkin.serviceName,以及server.port)以及controller对应的方法构造若干服务

service1 中访问http://localhost:8080/start需要访问http://localhost:9090/foo,则构造server2提供该方法

server2配置

com.zipkin.serviceName=service2
com.zipkin.url=http://110.173.14.57:9411
com.zipkin.connectTimeout=6000
com.zipkin.readTimeout=6000
com.zipkin.flushInterval=1
com.zipkin.compressionEnabled=true
server.port=9090

controller方法

@RequestMapping("foo")
public String foo() throws InterruptedException, IOException {
Random random = new Random();
int sleep= random.nextInt(100);
TimeUnit.MILLISECONDS.sleep(sleep);
Request request = new Request.Builder().url("http://localhost:9091/bar").get().build(); //service3
Response response = client.newCall(request).execute();
String result = response.body().string();
request = new Request.Builder().url("http://localhost:9092/tar").get().build(); //service4
response = client.newCall(request).execute();
result += response.body().string();
return " [service2 sleep " + sleep+" ms]" + result;
}

在server2中调用server3和server4中的方法

方法分别为

@RequestMapping("bar")
public String bar() throws InterruptedException, IOException { //service3 method
Random random = new Random();
int sleep= random.nextInt(100);
TimeUnit.MILLISECONDS.sleep(sleep);
return " [service3 sleep " + sleep+" ms]";
}
@RequestMapping("tar")
public String tar() throws InterruptedException, IOException { //service4 method
Random random = new Random();
int sleep= random.nextInt(1000);
TimeUnit.MILLISECONDS.sleep(sleep);
return " [service4 sleep " + sleep+" ms]";
}

将工程修改后编译成jar形式

执行

nohup java -jar server4.jar &
nohup java -jar server3.jar &
nohup java -jar server2.jar &
nohup java -jar server1.jar &

访问http://localhost:8080/start后查看zipkin的web UI

分布式系统监控系统zipkin入门

点击条目可以查看具体的延迟信息

分布式系统监控系统zipkin入门

服务之间的依赖为
分布式系统监控系统zipkin入门

brave 源码

以上完成了基本的操作，下面将从源码角度来看下brave的实现

首先从SpanCollector来入手

@Bean
public SpanCollector spanCollector() {
HttpSpanCollector.Config config = HttpSpanCollector.Config.builder().connectTimeout(properties.getConnectTimeout()).readTimeout(properties.getReadTimeout())
.compressionEnabled(properties.isCompressionEnabled()).flushInterval(properties.getFlushInterval()).build();
return HttpSpanCollector.create(properties.getUrl(), config, new EmptySpanCollectorMetricsHandler());
}

从名称上看HttpSpanCollector是基于http的span收集器,因此超时配置是必须的，默认给出的超时时间较长，flushInterval表示span的传递
间隔，实际为定时任务执行的间隔时间.在HttpSpanCollector中覆写了父类方法sendSpans

@Override
protected void sendSpans(byte[] json) throws IOException {
// intentionally not closing the connection, so as to use keep-alives
HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
connection.setConnectTimeout(config.connectTimeout());
connection.setReadTimeout(config.readTimeout());
connection.setRequestMethod("POST");
connection.addRequestProperty("Content-Type", "application/json");
if (config.compressionEnabled()) {
connection.addRequestProperty("Content-Encoding", "gzip");
ByteArrayOutputStream gzipped = new ByteArrayOutputStream();
try (GZIPOutputStream compressor = new GZIPOutputStream(gzipped)) {
compressor.write(json);
}
json = gzipped.toByteArray();
}
connection.setDoOutput(true);
connection.setFixedLengthStreamingMode(json.length);
connection.getOutputStream().write(json);
try (InputStream in = connection.getInputStream()) {
while (in.read() != -1) ; // skip
} catch (IOException e) {
try (InputStream err = connection.getErrorStream()) {
if (err != null) { // possible, if the connection was dropped
while (err.read() != -1) ; // skip
}
}
throw e;
}
}
}

可以看出最终span信息是通过HttpURLConnection实现的，同样道理就可以推理brave对brave-spring-resttemplate-interceptors模块的实现，
只是换了一种http封装。

Brave

@Bean
public Brave brave(SpanCollector spanCollector){
Brave.Builder builder = new Brave.Builder(properties.getServiceName()); //指定state
builder.spanCollector(spanCollector);
builder.traceSampler(Sampler.ALWAYS_SAMPLE);
Brave brave = builder.build();
return brave;
}

Brave类包装了各种工具类

public Brave build() {
return new Brave(this);
}

创建一个Brave

private Brave(Builder builder) {
serverTracer = ServerTracer.builder()
.randomGenerator(builder.random)
.spanCollector(builder.spanCollector)
.state(builder.state)
.traceSampler(builder.sampler).build();
clientTracer = ClientTracer.builder()
.randomGenerator(builder.random)
.spanCollector(builder.spanCollector)
.state(builder.state)
.traceSampler(builder.sampler).build();
localTracer = LocalTracer.builder()
.randomGenerator(builder.random)
.spanCollector(builder.spanCollector)
.spanAndEndpoint(SpanAndEndpoint.LocalSpanAndEndpoint.create(builder.state))
.traceSampler(builder.sampler).build();
serverRequestInterceptor = new ServerRequestInterceptor(serverTracer);
serverResponseInterceptor = new ServerResponseInterceptor(serverTracer);
clientRequestInterceptor = new ClientRequestInterceptor(clientTracer);
clientResponseInterceptor = new ClientResponseInterceptor(clientTracer);
serverSpanAnnotationSubmitter = AnnotationSubmitter.create(SpanAndEndpoint.ServerSpanAndEndpoint.create(builder.state));
serverSpanThreadBinder = new ServerSpanThreadBinder(builder.state);
clientSpanThreadBinder = new ClientSpanThreadBinder(builder.state);
}

封装了*Tracer,*Interceptor,*Binder等

其中 serverTracer当服务作为服务端时处理span信息，clientTracer当服务作为客户端时处理span信息

Filter

BraveServletFilter是http模块提供的拦截器功能，传递serverRequestInterceptor,serverResponseInterceptor,spanNameProvider等参数
其中spanNameProvider表示如何处理span的名称，默认使用method名称,spring boot中申明的filter bean 默认拦截所有请求

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null;
if (hasAlreadyFilteredAttribute) {
// Proceed without invoking this filter...
filterChain.doFilter(request, response);
} else {
final StatusExposingServletResponse statusExposingServletResponse = new StatusExposingServletResponse((HttpServletResponse) response);
requestInterceptor.handle(new HttpServerRequestAdapter(new ServletHttpServerRequest((HttpServletRequest) request), spanNameProvider));
try {
filterChain.doFilter(request, statusExposingServletResponse);
} finally {
responseInterceptor.handle(new HttpServerResponseAdapter(new HttpResponse() {
@Override
public int getHttpStatusCode() {
return statusExposingServletResponse.getStatus();
}
}));
}
}
}

首先来看requestInterceptor.handle方法，

public void handle(ServerRequestAdapter adapter) {
serverTracer.clearCurrentSpan();
final TraceData traceData = adapter.getTraceData();
Boolean sample = traceData.getSample();
if (sample != null && Boolean.FALSE.equals(sample)) {
serverTracer.setStateNoTracing();
LOGGER.fine("Received indication that we should NOT trace.");
} else {
if (traceData.getSpanId() != null) {
LOGGER.fine("Received span information as part of request.");
SpanId spanId = traceData.getSpanId();
serverTracer.setStateCurrentTrace(spanId.traceId, spanId.spanId,
spanId.nullableParentId(), adapter.getSpanName());
} else {
LOGGER.fine("Received no span state.");
serverTracer.setStateUnknown(adapter.getSpanName());
}
serverTracer.setServerReceived();
for(KeyValueAnnotation annotation : adapter.requestAnnotations())
{
serverTracer.submitBinaryAnnotation(annotation.getKey(), annotation.getValue());
}
}
}

其中serverTracer.clearCurrentSpan()清除当前线程上的span信息，调用ThreadLocalServerClientAndLocalSpanState中的

@Override
public void setCurrentServerSpan(final ServerSpan span) {
if (span == null) {
currentServerSpan.remove();
} else {
currentServerSpan.set(span);
}
}

currentServerSpan为ThreadLocal对象

private final static ThreadLocal<ServerSpan> currentServerSpan = new ThreadLocal<ServerSpan>() {

回到ServerRequestInterceptor#handle()方法中final TraceData traceData = adapter.getTraceData()

@Override
public TraceData getTraceData() {
final String sampled = serverRequest.getHttpHeaderValue(BraveHttpHeaders.Sampled.getName());
if (sampled != null) {
if (sampled.equals("0") || sampled.toLowerCase().equals("false")) {
return TraceData.builder().sample(false).build();
} else {
final String parentSpanId = serverRequest.getHttpHeaderValue(BraveHttpHeaders.ParentSpanId.getName());
final String traceId = serverRequest.getHttpHeaderValue(BraveHttpHeaders.TraceId.getName());
final String spanId = serverRequest.getHttpHeaderValue(BraveHttpHeaders.SpanId.getName());
if (traceId != null && spanId != null) {
SpanId span = getSpanId(traceId, spanId, parentSpanId);
return TraceData.builder().sample(true).spanId(span).build();
}
}
}
return TraceData.builder().build();
}

其中SpanId span = getSpanId(traceId, spanId, parentSpanId) 将构造一个SpanId对象

private SpanId getSpanId(String traceId, String spanId, String parentSpanId) {
return SpanId.builder()
.traceId(convertToLong(traceId))
.spanId(convertToLong(spanId))
.parentId(parentSpanId == null ? null : convertToLong(parentSpanId)).build();
}

将traceId,spanId,parentId关联起来，其中设置parentId方法为

public Builder parentId(@Nullable Long parentId) {
if (parentId == null) {
this.flags |= FLAG_IS_ROOT;
} else {
this.flags &= ~FLAG_IS_ROOT;
}
this.parentId = parentId;
return this;
}

如果parentId为空为根节点，则执行this.flags |= FLAG_IS_ROOT ,因此后续在判断节点是否为根节点时，只需要执行(flags & FLAG_IS_ROOT) == FLAG_IS_ROOT即可.

构造完SpanId后看

serverTracer.setStateCurrentTrace(spanId.traceId, spanId.spanId,
spanId.nullableParentId(), adapter.getSpanName());

设置当前Span

public void setStateCurrentTrace(long traceId, long spanId, @Nullable Long parentSpanId, @Nullable String name) {
checkNotBlank(name, "Null or blank span name");
spanAndEndpoint().state().setCurrentServerSpan(
ServerSpan.create(traceId, spanId, parentSpanId, name));
}

ServerSpan.create创建Span信息

static ServerSpan create(long traceId, long spanId, @Nullable Long parentSpanId, String name) {
Span span = new Span();
span.setTrace_id(traceId);
span.setId(spanId);
if (parentSpanId != null) {
span.setParent_id(parentSpanId);
}
span.setName(name);
return create(span, true);
}

构造了一个包含Span信息的AutoValue_ServerSpan对象

通过setCurrentServerSpan设置到当前线程上

继续看serverTracer.setServerReceived()方法

public void setServerReceived() {
submitStartAnnotation(zipkinCoreConstants.SERVER_RECV);
}

为当前请求设置了server received event

void submitStartAnnotation(String annotationName) {
Span span = spanAndEndpoint().span();
if (span != null) {
Annotation annotation = Annotation.create(
currentTimeMicroseconds(),
annotationName,
spanAndEndpoint().endpoint()
);
synchronized (span) {
span.setTimestamp(annotation.timestamp);
span.addToAnnotations(annotation);
}
}
}

在这里为Span信息设置了Annotation信息,后续的

for(KeyValueAnnotation annotation : adapter.requestAnnotations())
{
serverTracer.submitBinaryAnnotation(annotation.getKey(), annotation.getValue());
}

设置了BinaryAnnotation信息，adapter.requestAnnotations()在构造HttpServerRequestAdapter时已完成

@Override
public Collection<KeyValueAnnotation> requestAnnotations() {
KeyValueAnnotation uriAnnotation = KeyValueAnnotation.create(
TraceKeys.HTTP_URL, serverRequest.getUri().toString());
return Collections.singleton(uriAnnotation);
}

以上将Span信息(包括sr)存储在当前线程中，接下来继续看BraveServletFilter#doFilter方法的finally部分

responseInterceptor.handle(new HttpServerResponseAdapter(new HttpResponse() {
@Override //获取http状态码
public int getHttpStatusCode() {
return statusExposingServletResponse.getStatus();
}
}));

handle方法

public void handle(ServerResponseAdapter adapter) {
// We can submit this in any case. When server state is not set or
// we should not trace this request nothing will happen.
LOGGER.fine("Sending server send.");
try {
for(KeyValueAnnotation annotation : adapter.responseAnnotations())
{
serverTracer.submitBinaryAnnotation(annotation.getKey(), annotation.getValue());
}
serverTracer.setServerSend();
} finally {
serverTracer.clearCurrentSpan();
}
}

首先配置BinaryAnnotation信息，然后执行serverTracer.setServerSend,在finally中清除当前线程中的Span信息(不管前面是否清楚成功,最终都将执行该不走)，ThreadLocal中的数据要做到有始有终

看serverTracer.setServerSend()

public void setServerSend() {
if (submitEndAnnotation(zipkinCoreConstants.SERVER_SEND, spanCollector())) {
spanAndEndpoint().state().setCurrentServerSpan(null);
}
}

终于看到spanCollector收集器了，说明下面将看是收集Span信息,这里为ss注解

boolean submitEndAnnotation(String annotationName, SpanCollector spanCollector) {
Span span = spanAndEndpoint().span();
if (span == null) {
return false;
}
Annotation annotation = Annotation.create(
currentTimeMicroseconds(),
annotationName,
spanAndEndpoint().endpoint()
);
span.addToAnnotations(annotation);
if (span.getTimestamp() != null) {
span.setDuration(annotation.timestamp - span.getTimestamp());
}
spanCollector.collect(span);
return true;
}

首先获取当前线程中的Span信息，然后处理注解信息，通过annotation.timestamp - span.getTimestamp()计算延迟,
调用spanCollector.collect(span)进行收集Span信息，那么Span信息是同步收集的吗？肯定不是的，接着看

分布式系统监控系统zipkin入门

调用spanCollector.collect(span)则执行FlushingSpanCollector中的collect方法

@Override
public void collect(Span span) {
metrics.incrementAcceptedSpans(1);
if (!pending.offer(span)) {
metrics.incrementDroppedSpans(1);
}
}

首先进行的是metrics统计信息，可以自定义该SpanCollectorMetricsHandler信息收集各指标信息,利用如grafana等展示信息

pending.offer(span)将span信息存储在BlockingQueue中，然后通过定时任务去取出阻塞队列中的值，偷偷摸摸的上传span信息

定时任务利用了Flusher类来执行，在构造FlushingSpanCollector时构造了Flusher类

static final class Flusher implements Runnable {
final Flushable flushable;
final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
Flusher(Flushable flushable, int flushInterval) {
this.flushable = flushable;
this.scheduler.scheduleWithFixedDelay(this, 0, flushInterval, SECONDS);
}
@Override
public void run() {
try {
flushable.flush();
} catch (IOException ignored) {
}
}
}

创建了一个核心线程数为1的线程池，每间隔flushInterval秒执行一次Span信息上传，执行flush方法

@Override
public void flush() {
if (pending.isEmpty()) return;
List<Span> drained = new ArrayList<Span>(pending.size());
pending.drainTo(drained);
if (drained.isEmpty()) return;
int spanCount = drained.size();
try {
reportSpans(drained);
} catch (IOException e) {
metrics.incrementDroppedSpans(spanCount);
} catch (RuntimeException e) {
metrics.incrementDroppedSpans(spanCount);
}
}

首先将阻塞队列中的值全部取出存如集合中，最后调用reportSpans(List<Span> drained)抽象方法，该方法在AbstractSpanCollector得到覆写

@Override
protected void reportSpans(List<Span> drained) throws IOException {
byte[] encoded = codec.writeSpans(drained);
sendSpans(encoded);
}

转换成字节流后调用sendSpans抽象方法发送Span信息，此时就回到一开始说的HttpSpanCollector通过HttpURLConnection实现的sendSpans方法。

具体使用可以参考：https://github.com/liaokailin/zipkin#architecture，下载这个maven项目并按照里面的说明运行即可。