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<title>1. Spring Cloud Context: Application Context Services</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-commons.html" title="Cloud Native Applications"><link rel="up" href="multi_spring-cloud-commons.html" title="Cloud Native Applications"><link rel="prev" href="multi_pr01.html" title=""><link rel="next" href="multi__spring_cloud_commons_common_abstractions.html" title="2. Spring Cloud Commons: Common Abstractions"></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">1. Spring Cloud Context: Application Context Services</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi_pr01.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="multi__spring_cloud_commons_common_abstractions.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_spring_cloud_context_application_context_services" href="#_spring_cloud_context_application_context_services"></a>1. Spring Cloud Context: Application Context Services</h1></div></div></div><p>Spring Boot has an opinionated view of how to build an application with Spring.
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<title>1. Spring Cloud Context: Application Context Services</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-commons.html" title="Cloud Native Applications"><link rel="up" href="multi_spring-cloud-commons.html" title="Cloud Native Applications"><link rel="prev" href="multi_pr01.html" title=""><link rel="next" href="multi__spring_cloud_commons_common_abstractions.html" title="2. Spring Cloud Commons: Common Abstractions"></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">1. Spring Cloud Context: Application Context Services</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi_pr01.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="multi__spring_cloud_commons_common_abstractions.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="_spring_cloud_context_application_context_services" href="#_spring_cloud_context_application_context_services"></a>1. Spring Cloud Context: Application Context Services</h1></div></div></div><p>Spring Boot has an opinionated view of how to build an application with Spring.
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For instance, it has conventional locations for common configuration files and has endpoints for common management and monitoring tasks.
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Spring Cloud builds on top of that and adds a few features that probably all components in a system would use or occasionally need.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_the_bootstrap_application_context" href="#_the_bootstrap_application_context"></a>1.1 The Bootstrap Application Context</h2></div></div></div><p>A Spring Cloud application operates by creating a “bootstrap” context, which is a parent context for the main application.
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Spring Cloud builds on top of that and adds a few features that probably all components in a system would use or occasionally need.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_the_bootstrap_application_context" href="#_the_bootstrap_application_context"></a>1.1 The Bootstrap Application Context</h2></div></div></div><p>A Spring Cloud application operates by creating a <span class="quote">“<span class="quote">bootstrap</span>”</span> context, which is a parent context for the main application.
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It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files.
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The two contexts share an <code class="literal">Environment</code>, which is the source of external properties for any Spring application.
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By default, bootstrap properties (not <code class="literal">bootstrap.properties</code> but properties that are loaded during the bootstrap phase) are added with high precedence, so they cannot be overridden by local configuration.</p><p>The bootstrap context uses a different convention for locating external configuration than the main application context.
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@@ -16,16 +16,16 @@ The following listing shows an example:</p><p><b>bootstrap.yml. </b>
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config:
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uri: ${SPRING_CONFIG_URI:http://localhost:8888}</pre><p>
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</p><p>If your application needs any application-specific configuration from the server, it is a good idea to set the <code class="literal">spring.application.name</code> (in <code class="literal">bootstrap.yml</code> or <code class="literal">application.yml</code>).</p><p>You can disable the bootstrap process completely by setting <code class="literal">spring.cloud.bootstrap.enabled=false</code> (for example, in system properties).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_application_context_hierarchies" href="#_application_context_hierarchies"></a>1.2 Application Context Hierarchies</h2></div></div></div><p>If you build an application context from <code class="literal">SpringApplication</code> or <code class="literal">SpringApplicationBuilder</code>, then the Bootstrap context is added as a parent to that context.
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It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the “main” application context contains additional property sources, compared to building the same context without Spring Cloud Config.
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The additional property sources are:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">“bootstrap”: If any <code class="literal">PropertySourceLocators</code> are found in the Bootstrap context and if they have non-empty properties, an optional <code class="literal">CompositePropertySource</code> appears with high priority.
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It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the <span class="quote">“<span class="quote">main</span>”</span> application context contains additional property sources, compared to building the same context without Spring Cloud Config.
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The additional property sources are:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="quote">“<span class="quote">bootstrap</span>”</span>: If any <code class="literal">PropertySourceLocators</code> are found in the Bootstrap context and if they have non-empty properties, an optional <code class="literal">CompositePropertySource</code> appears with high priority.
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An example would be properties from the Spring Cloud Config Server.
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See “<a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-property-sources" title="1.6 Customizing the Bootstrap Property Sources">Section 1.6, “Customizing the Bootstrap Property Sources”</a>” for instructions on how to customize the contents of this property source.</li><li class="listitem">“applicationConfig: [classpath:bootstrap.yml]” (and related files if Spring profiles are active): If you have a <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>), those properties are used to configure the Bootstrap context.
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See <span class="quote">“<span class="quote"><a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-property-sources" title="1.6 Customizing the Bootstrap Property Sources">Section 1.6, “Customizing the Bootstrap Property Sources”</a></span>”</span> for instructions on how to customize the contents of this property source.</li><li class="listitem"><span class="quote">“<span class="quote">applicationConfig: [classpath:bootstrap.yml]</span>”</span> (and related files if Spring profiles are active): If you have a <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>), those properties are used to configure the Bootstrap context.
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Then they get added to the child context when its parent is set.
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They have lower precedence than the <code class="literal">application.yml</code> (or <code class="literal">.properties</code>) and any other property sources that are added to the child as a normal part of the process of creating a Spring Boot application.
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See “<a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-properties" title="1.3 Changing the Location of Bootstrap Properties">Section 1.3, “Changing the Location of Bootstrap Properties”</a>” for instructions on how to customize the contents of these property sources.</li></ul></div><p>Because of the ordering rules of property sources, the “bootstrap” entries take precedence.
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See <span class="quote">“<span class="quote"><a class="xref" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-properties" title="1.3 Changing the Location of Bootstrap Properties">Section 1.3, “Changing the Location of Bootstrap Properties”</a></span>”</span> for instructions on how to customize the contents of these property sources.</li></ul></div><p>Because of the ordering rules of property sources, the <span class="quote">“<span class="quote">bootstrap</span>”</span> entries take precedence.
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However, note that these do not contain any data from <code class="literal">bootstrap.yml</code>, which has very low precedence but can be used to set defaults.</p><p>You can extend the context hierarchy by setting the parent context of any <code class="literal">ApplicationContext</code> you create — for example, by using its own interface or with the <code class="literal">SpringApplicationBuilder</code> convenience methods (<code class="literal">parent()</code>, <code class="literal">child()</code> and <code class="literal">sibling()</code>).
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The bootstrap context is the parent of the most senior ancestor that you create yourself.
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Every context in the hierarchy has its own “bootstrap” (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants.
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Every context in the hierarchy has its own <span class="quote">“<span class="quote">bootstrap</span>”</span> (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants.
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If there is a Config Server, every context in the hierarchy can also (in principle) have a different <code class="literal">spring.application.name</code> and, hence, a different remote property source.
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Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in
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the parent, by name and also by property source name.
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Those properties behave like the <code class="literal">spring.config.*</code> variants with the same name.
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In fact, they are used to set up the bootstrap <code class="literal">ApplicationContext</code> by setting those properties in its <code class="literal">Environment</code>.
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If there is an active profile (from <code class="literal">spring.profiles.active</code> or through the <code class="literal">Environment</code> API in the
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context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app — for example, from <code class="literal">bootstrap-development.properties</code> for a <code class="literal">development</code> profile.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="overriding-bootstrap-properties" href="#overriding-bootstrap-properties"></a>1.4 Overriding the Values of Remote Properties</h2></div></div></div><p>The property sources that are added to your application by the bootstrap context are often “remote” (from example, from Spring Cloud Config Server).
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context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app — for example, from <code class="literal">bootstrap-development.properties</code> for a <code class="literal">development</code> profile.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="overriding-bootstrap-properties" href="#overriding-bootstrap-properties"></a>1.4 Overriding the Values of Remote Properties</h2></div></div></div><p>The property sources that are added to your application by the bootstrap context are often <span class="quote">“<span class="quote">remote</span>”</span> (from example, from Spring Cloud Config Server).
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By default, they cannot be overridden locally.
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If you want to let your applications override the remote properties with their own System properties or config files, the remote property source has to grant it permission by setting <code class="literal">spring.cloud.config.allowOverride=true</code> (it does not work to set this locally).
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Once that flag is set, two finer-grained settings control the location of the remote properties in relation to system properties and the application’s local configuration:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="literal">spring.cloud.config.overrideNone=true</code>: Override from any local property source.</li><li class="listitem"><code class="literal">spring.cloud.config.overrideSystemProperties=false</code>: Only system properties, command line arguments, and environment variables (but not the local config files) should override the remote settings.</li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_customizing_the_bootstrap_configuration" href="#_customizing_the_bootstrap_configuration"></a>1.5 Customizing the Bootstrap Configuration</h2></div></div></div><p>The bootstrap context can be set to do anything you like by adding entries to <code class="literal">/META-INF/spring.factories</code> under a key named <code class="literal">org.springframework.cloud.bootstrap.BootstrapConfiguration</code>.
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This holds a comma-separated list of Spring <code class="literal">@Configuration</code> classes that are used to create the context.
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Any beans that you want to be available to the main application context for autowiring can be created here.
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There is a special contract for <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code>.
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If you want to control the startup sequence, classes can be marked with an <code class="literal">@Order</code> annotation (the default order is <code class="literal">last</code>).</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="images/warning.png"></td><th align="left">Warning</th></tr><tr><td align="left" valign="top"><p>When adding custom <code class="literal">BootstrapConfiguration</code>, be careful that the classes you add are not <code class="literal">@ComponentScanned</code> by mistake into your “main” application context, where they might not be needed.
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If you want to control the startup sequence, classes can be marked with an <code class="literal">@Order</code> annotation (the default order is <code class="literal">last</code>).</p><div class="warning" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Warning"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="images/warning.png"></td><th align="left">Warning</th></tr><tr><td align="left" valign="top"><p>When adding custom <code class="literal">BootstrapConfiguration</code>, be careful that the classes you add are not <code class="literal">@ComponentScanned</code> by mistake into your <span class="quote">“<span class="quote">main</span>”</span> application context, where they might not be needed.
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Use a separate package name for boot configuration classes and make sure that name is not already covered by your <code class="literal">@ComponentScan</code> or <code class="literal">@SpringBootApplication</code> annotated configuration classes.</p></td></tr></table></div><p>The bootstrap process ends by injecting initializers into the main <code class="literal">SpringApplication</code> instance (which is the normal Spring Boot startup sequence, whether it is running as a standalone application or deployed in an application server).
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First, a bootstrap context is created from the classes found in <code class="literal">spring.factories</code>.
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Then, all <code class="literal">@Beans</code> of type <code class="literal">ApplicationContextInitializer</code> are added to the main <code class="literal">SpringApplication</code> before it is started.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-property-sources" href="#customizing-bootstrap-property-sources"></a>1.6 Customizing the Bootstrap Property Sources</h2></div></div></div><p>The default property source for external configuration added by the bootstrap process is the Spring Cloud Config Server, but you can add additional sources by adding beans of type <code class="literal">PropertySourceLocator</code> to the bootstrap context (through <code class="literal">spring.factories</code>).
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