目前 SOFATracer 提供了两种采样模式，一种是基于 BitSet 实现的采用固定采样率的采样模式，另外一种是提供给用户自定义实现采样的采样模式。
本文将通过示例来演示如何使用。本示例基于 tracer-sample-with-springmvc 工程，除 application.properties 之外，其他均相同。
基于固定采样率的采样模式
在 application.properties 中增加采样相关配置项
#采样率 0~100
com.alipay.sofa.tracer.samplerPercentage=100
#采样模式类型名称
com.alipay.sofa.tracer.samplerName=PercentageBasedSampler验证方式
当采样率设置为 100 时，每次都会打印摘要日志。
当采样率设置为 0 时，不打印。
当采样率设置为 0~100 之间时，按概率打印。
以请求 10 次来验证下结果。
当采样率设置为 100 时，每次都会打印摘要日志。 启动工程，浏览器中输入：http://localhost:8080/springmvc ，并且刷新地址10次，查看日志如下：
{"time":"2018-11-09 11:54:47.643","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173568757510019269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":68,"current.thread.name":"http-nio-8080-exec-1","baggage":""} {"time":"2018-11-09 11:54:50.980","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569097710029269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":3,"current.thread.name":"http-nio-8080-exec-2","baggage":""} {"time":"2018-11-09 11:54:51.542","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569153910049269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":3,"current.thread.name":"http-nio-8080-exec-4","baggage":""} {"time":"2018-11-09 11:54:52.061","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569205910069269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-6","baggage":""} {"time":"2018-11-09 11:54:52.560","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569255810089269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-8","baggage":""} {"time":"2018-11-09 11:54:52.977","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569297610109269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":1,"current.thread.name":"http-nio-8080-exec-10","baggage":""} {"time":"2018-11-09 11:54:53.389","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569338710129269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-2","baggage":""} {"time":"2018-11-09 11:54:53.742","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569374110149269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":1,"current.thread.name":"http-nio-8080-exec-4","baggage":""} {"time":"2018-11-09 11:54:54.142","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569414010169269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-6","baggage":""} {"time":"2018-11-09 11:54:54.565","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173569456310189269","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-8","baggage":""}当采样率设置为 0 时，不打印日志。 启动工程，浏览器中输入：http://localhost:8080/springmvc ；并且刷新地址 10 次，查看
./logs/tracerlog/目录，没有 spring-mvc-digest.log 日志文件当采样率设置为 0~100 之间时，按概率打印日志。 此处设置采样率为 20。
刷新 10 次请求
{"time":"2018-11-09 12:14:29.466","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173686946410159846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-5","baggage":""} {"time":"2018-11-09 12:15:21.776","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173692177410319846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-2","baggage":""}刷新 20 次请求
{"time":"2018-11-09 12:14:29.466","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173686946410159846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-5","baggage":""} {"time":"2018-11-09 12:15:21.776","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173692177410319846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-2","baggage":""} {"time":"2018-11-09 12:15:22.439","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173692243810359846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":1,"current.thread.name":"http-nio-8080-exec-6","baggage":""} {"time":"2018-11-09 12:15:22.817","local.app":"SOFATracerSpringMVC","traceId":"0a0fe8ec154173692281510379846","spanId":"0.1","request.url":"http://localhost:8080/springmvc","method":"GET","result.code":"200","req.size.bytes":-1,"resp.size.bytes":0,"time.cost.milliseconds":2,"current.thread.name":"http-nio-8080-exec-8","baggage":""}说明按 20% 进行采样，测试结果仅供参考。
自定义采样模式
SOFATracer 中提供了一个采样率计算的接口 Sampler ，如果你需要定制化自己的采样策略，可通过实现此接口来进行扩展。下面通过一个简单示例来演示如何使用自定义采样模式。
自定义采样规则类
public class CustomOpenRulesSamplerRuler implements Sampler{
private static final String TYPE ="CustomOpenRulesSamplerRuler";
@Override
public SamplingStatus sample(SofaTracerSpan sofaTracerSpan){
SamplingStatus samplingStatus =new SamplingStatus();
Map<String,Object> tags =new HashMap<String,Object>();
tags.put(SofaTracerConstant.SAMPLER_TYPE_TAG_KEY, TYPE);
tags =Collections.unmodifiableMap(tags);
samplingStatus.setTags(tags);
if(sofaTracerSpan.isServer()){
samplingStatus.setSampled(false);
}else{
samplingStatus.setSampled(true);
}
return samplingStatus;
}
@Override
public String getType(){
return TYPE;
}
@Override
public void close(){
// do nothing
}
}
在 sample 方法中，用户可以根据当前 sofaTracerSpan 提供的信息来决定是否进行打印。这个案例是通过判断 isServer 来决定是否采样，isServer=true 即不采样，否则采样。
在 application.properties 中增加采样相关配置项
com.alipay.sofa.tracer.samplerName.samplerCustomRuleClassName=com.alipay.sofa.tracer.examples.springmvc.sampler.CustomOpenRulesSamplerRuler相关试验结果，您可以自行验证。
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