# 插件开发指南

span = ContextManager.createExitSpan("/span/operation/name", contextCarrier, "ip:port");
CarrierItem next = contextCarrier.items();
while (next.hasNext()) {
    next = next.next();
    httpRequest.setHeader(next.getHeadKey(), next.getHeadValue());
}

ContextCarrier contextCarrier = new ContextCarrier();
CarrierItem next = contextCarrier.items();
while (next.hasNext()) {
    next = next.next();
    next.setHeadValue(request.getHeader(next.getHeadKey()));
}

span = ContextManager.createEntrySpan("/span/operation/name", contextCarrier);

public static AbstractSpan createEntrySpan(String endpointName, ContextCarrier carrier)

public static AbstractSpan createLocalSpan(String endpointName)

public static AbstractSpan createExitSpan(String endpointName, ContextCarrier carrier, String remotePeer)

/**
 * Set the component id, which defines in {@link ComponentsDefine}
 *
 * @param component
 * @return the span for chaining.
 */
AbstractSpan setComponent(Component component);

/**
 * Only use this method in explicit instrumentation, like opentracing-skywalking-bridge.
 * It it higher recommend don't use this for performance consideration.
 *
 * @param componentName
 * @return the span for chaining.
 */
AbstractSpan setComponent(String componentName);

AbstractSpan setLayer(SpanLayer layer);

/**
 * Set a key:value tag on the Span.
 *
 * @return this Span instance, for chaining
 */
AbstractSpan tag(String key, String value);

/**
 * Record an exception event of the current walltime timestamp.
 *
 * @param t any subclass of {@link Throwable}, which occurs in this span.
 * @return the Span, for chaining
 */
AbstractSpan log(Throwable t);

AbstractSpan errorOccurred();

/**
 * Record an event at a specific timestamp.
 *
 * @param timestamp The explicit timestamp for the log record.
 * @param event the events
 * @return the Span, for chaining
 */
AbstractSpan log(long timestamp, Map<String, ?> event);

/**
 * Sets the string name for the logical operation this span represents.
 *
 * @return this Span instance, for chaining
 */
AbstractSpan setOperationName(String endpointName);

/**
 * The span finish at current tracing context, but the current span is still alive, until {@link #asyncFinish}
 * called.
 *
 * This method must be called<br/>
 * 1. In original thread(tracing context).
 * 2. Current span is active span.
 *
 * During alive, tags, logs and attributes of the span could be changed, in any thread.
 *
 * The execution times of {@link #prepareForAsync} and {@link #asyncFinish()} must match.
 *
 * @return the current span
 */
AbstractSpan prepareForAsync();

/**
 * Notify the span, it could be finished.
 *
 * The execution times of {@link #prepareForAsync} and {@link #asyncFinish()} must match.
 *
 * @return the current span
 */
AbstractSpan asyncFinish();

protected abstract ClassMatch enhanceClass();

@Override
protected ClassMatch enhanceClassName() {
    return byName("org.apache.catalina.core.StandardEngineValve");		
}

protected InstanceMethodsInterceptPoint[] getInstanceMethodsInterceptPoints();

public interface InstanceMethodsInterceptPoint {
    /**
     * class instance methods matcher.
     *
     * @return methods matcher
     */
    ElementMatcher<MethodDescription> getMethodsMatcher();

    /**
     * @return represents a class name, the class instance must instanceof InstanceMethodsAroundInterceptor.
     */
    String getMethodsInterceptor();

    boolean isOverrideArgs();
}

/**
 * A interceptor, which intercept method's invocation. The target methods will be defined in {@link
 * ClassEnhancePluginDefine}'s subclass, most likely in {@link ClassInstanceMethodsEnhancePluginDefine}
 *
 * @author wusheng
 */
public interface InstanceMethodsAroundInterceptor {
    /**
     * called before target method invocation.
     *
     * @param result change this result, if you want to truncate the method.
     * @throws Throwable
     */
    void beforeMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes,
        MethodInterceptResult result) throws Throwable;

    /**
     * called after target method invocation. Even method's invocation triggers an exception.
     *
     * @param ret the method's original return value.
     * @return the method's actual return value.
     * @throws Throwable
     */
    Object afterMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes,
        Object ret) throws Throwable;

    /**
     * called when occur exception.
     *
     * @param t the exception occur.
     */
    void handleMethodException(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes,
        Throwable t);
}