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<title>11. Managing Spans with Annotations</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud-sleuth.html" title="Spring Cloud Sleuth"><link rel="up" href="multi_spring-cloud-sleuth.html" title="Spring Cloud Sleuth"><link rel="prev" href="multi__naming_spans.html" title="10. Naming spans"><link rel="next" href="multi__customizations.html" title="12. Customizations"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">11. Managing Spans with Annotations</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__naming_spans.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="multi__customizations.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_managing_spans_with_annotations" href="#_managing_spans_with_annotations"></a>11. Managing Spans with Annotations</h1></div></div></div><p>You can manage spans with a variety of annotations.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_rationale" href="#_rationale"></a>11.1 Rationale</h2></div></div></div><p>There are a number of good reasons to manage spans with annotations, including:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">API-agnostic means to collaborate with a span. Use of annotations lets users add to a span with no library dependency on a span api.
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Doing so lets Sleuth change its core API to create less impact to user code.</li><li class="listitem">Reduced surface area for basic span operations. Without this feature, you must use the span api, which has lifecycle commands that could be used incorrectly.
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By only exposing scope, tag, and log functionality, you can collaborate without accidentally breaking span lifecycle.</li><li class="listitem">Collaboration with runtime generated code. With libraries such as Spring Data and Feign, the implementations of interfaces are generated at runtime.
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Consequently, span wrapping of objects was tedious.
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Now you can provide annotations over interfaces and the arguments of those interfaces.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_creating_new_spans" href="#_creating_new_spans"></a>11.2 Creating New Spans</h2></div></div></div><p>If you do not want to create local spans manually, you can use the <code class="literal">@NewSpan</code> annotation.
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Also, we provide the <code class="literal">@SpanTag</code> annotation to add tags in an automated fashion.</p><p>Now we can consider some examples of usage.</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> testMethod();</pre><p>Annotating the method without any parameter leads to creating a new span whose name equals the annotated method name.</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan("customNameOnTestMethod4")</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> testMethod4();</pre><p>If you provide the value in the annotation (either directly or by setting the <code class="literal">name</code> parameter), the created span has the provided value as the name.</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// method declaration</span>
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<em><span class="hl-annotation" style="color: gray">@NewSpan(name = "customNameOnTestMethod5")</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> testMethod5(<em><span class="hl-annotation" style="color: gray">@SpanTag("testTag")</span></em> String param);
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// and method execution</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.testBean.testMethod5(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"test"</span>);</pre><p>You can combine both the name and a tag. Let’s focus on the latter.
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In this case, the value of the annotated method’s parameter runtime value becomes the value of the tag.
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In our sample, the tag key is <code class="literal">testTag</code>, and the tag value is <code class="literal">test</code>.</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan(name = "customNameOnTestMethod3")</span></em>
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<em><span class="hl-annotation" style="color: gray">@Override</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> testMethod3() {
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}</pre><p>You can place the <code class="literal">@NewSpan</code> annotation on both the class and an interface.
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If you override the interface’s method and provide a different value for the <code class="literal">@NewSpan</code> annotation, the most
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concrete one wins (in this case <code class="literal">customNameOnTestMethod3</code> is set).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_continuing_spans" href="#_continuing_spans"></a>11.3 Continuing Spans</h2></div></div></div><p>If you want to add tags and annotations to an existing span, you can use the <code class="literal">@ContinueSpan</code> annotation, as shown in the following example:</p><pre class="programlisting"><span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// method declaration</span>
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<em><span class="hl-annotation" style="color: gray">@ContinueSpan(log = "testMethod11")</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> testMethod11(<em><span class="hl-annotation" style="color: gray">@SpanTag("testTag11")</span></em> String param);
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// method execution</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.testBean.testMethod11(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"test"</span>);
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">this</span>.testBean.testMethod13();</pre><p>(Note that, in contrast with the <code class="literal">@NewSpan</code> annotation ,you can also add logs with the <code class="literal">log</code> parameter.)</p><p>That way, the span gets continued and:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Log entries named <code class="literal">testMethod11.before</code> and <code class="literal">testMethod11.after</code> are created.</li><li class="listitem">If an exception is thrown, a log entry named <code class="literal">testMethod11.afterFailure</code> is also created.</li><li class="listitem">A tag with a key of <code class="literal">testTag11</code> and a value of <code class="literal">test</code> is created.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_advanced_tag_setting" href="#_advanced_tag_setting"></a>11.4 Advanced Tag Setting</h2></div></div></div><p>There are 3 different ways to add tags to a span. All of them are controlled by the <code class="literal">SpanTag</code> annotation.
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The precedence is as follows:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">Try with a bean of <code class="literal">TagValueResolver</code> type and a provided name.</li><li class="listitem">If the bean name has not been provided, try to evaluate an expression.
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We search for a <code class="literal">TagValueExpressionResolver</code> bean.
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The default implementation uses SPEL expression resolution.
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<span class="strong"><strong>IMPORTANT</strong></span> You can only reference properties from the SPEL expression. Method execution is not allowed due to security constraints.</li><li class="listitem">If we do not find any expression to evaluate, return the <code class="literal">toString()</code> value of the parameter.</li></ol></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_custom_extractor" href="#_custom_extractor"></a>11.4.1 Custom extractor</h3></div></div></div><p>The value of the tag for the following method is computed by an implementation of <code class="literal">TagValueResolver</code> interface.
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Its class name has to be passed as the value of the <code class="literal">resolver</code> attribute.</p><p>Consider the following annotated method:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> getAnnotationForTagValueResolver(
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<em><span class="hl-annotation" style="color: gray">@SpanTag(key = "test", resolver = TagValueResolver.class)</span></em> String test) {
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}</pre><p>Now further consider the following <code class="literal">TagValueResolver</code> bean implementation:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Bean(name = "myCustomTagValueResolver")</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> TagValueResolver tagValueResolver() {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> parameter -> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"Value from myCustomTagValueResolver"</span>;
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}</pre><p>The two preceding examples lead to setting a tag value equal to <code class="literal">Value from myCustomTagValueResolver</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_resolving_expressions_for_a_value" href="#_resolving_expressions_for_a_value"></a>11.4.2 Resolving Expressions for a Value</h3></div></div></div><p>Consider the following annotated method:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> getAnnotationForTagValueExpression(
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<em><span class="hl-annotation" style="color: gray">@SpanTag(key = "test", expression = "'hello' + ' characters'")</span></em> String test) {
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}</pre><p>No custom implementation of a <code class="literal">TagValueExpressionResolver</code> leads to evaluation of the SPEL expression, and a tag with a value of <code class="literal">4 characters</code> is set on the span.
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If you want to use some other expression resolution mechanism, you can create your own implementation of the bean.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_using_the_tostring_method" href="#_using_the_tostring_method"></a>11.4.3 Using the <code class="literal">toString()</code> method</h3></div></div></div><p>Consider the following annotated method:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@NewSpan</span></em>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> getAnnotationForArgumentToString(<em><span class="hl-annotation" style="color: gray">@SpanTag("test")</span></em> Long param) {
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}</pre><p>Running the preceding method with a value of <code class="literal">15</code> leads to setting a tag with a String value of <code class="literal">"15"</code>.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__naming_spans.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="multi__customizations.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">10. Naming spans </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-sleuth.html">Home</a></td><td width="40%" align="right" valign="top"> 12. Customizations</td></tr></table></div></body></html> |