skywalking-java/docs/en/setup/service-agent/java-agent/Application-toolkit-trace.md

• Dependency the toolkit, such as using maven or gradle

   <dependency>
      <groupId>org.apache.skywalking</groupId>
      <artifactId>apm-toolkit-trace</artifactId>
      <version>${skywalking.version}</version>
   </dependency>

• Use TraceContext.traceId() API to obtain traceId.

import TraceContext;
...

modelAndView.addObject("traceId", TraceContext.traceId());

Sample codes only

• Add @Trace to any method you want to trace. After that, you can see the span in the Stack.

• Methods annotated with @Tag will try to tag the current active span with the given key (Tag#key()) and (Tag#value()), if there is no active span at all, this annotation takes no effect. @Tag can be repeated, and can be used in companion with @Trace, see examples below. The value of Tag is the same as what are supported in Customize Enhance Trace.

• Add custom tag in the context of traced method, ActiveSpan.tag("key", "val").

• ActiveSpan.error() Mark the current span as error status.

• ActiveSpan.error(String errorMsg) Mark the current span as error status with a message.

• ActiveSpan.error(Throwable throwable) Mark the current span as error status with a Throwable.

• ActiveSpan.debug(String debugMsg) Add a debug level log message in the current span.

• ActiveSpan.info(String infoMsg) Add an info level log message in the current span.

ActiveSpan.tag("my_tag", "my_value");
ActiveSpan.error();
ActiveSpan.error("Test-Error-Reason");

ActiveSpan.error(new RuntimeException("Test-Error-Throwable"));
ActiveSpan.info("Test-Info-Msg");
ActiveSpan.debug("Test-debug-Msg");

/**
 * The codes below will generate a span,
 * and two tags, keys are `tag1` and `tag2`, values are the passed-in parameters, respectively
 */
@Trace
@Tag(key = "tag1", value = "arg[0]")
@Tag(key = "tag2", value = "arg[1]")
public void methodYouWantToTrace(String param1, String param2) {
    // ...
}