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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 V1.78.1"><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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<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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@@ -38,6 +38,6 @@ Its class name has to be passed as the value of the <code class="literal">resolv
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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(<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_literal_tostring_literal_method" href="#_using_the_literal_tostring_literal_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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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>
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