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190 lines
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190 lines
24 KiB
7 years ago
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<html><head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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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
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with Spring: for instance it has conventional locations for common
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configuration file, and endpoints for common management and monitoring
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tasks. Spring Cloud builds on top of that and adds a few features that
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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"
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context, which is a parent context for the main application. Out of
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the box it is responsible for loading configuration properties from
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the external sources, and also decrypting properties in the local
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external configuration files. The two contexts share an <code class="literal">Environment</code>
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which is the source of external properties for any Spring
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application. Bootstrap properties are added with high precedence, so
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they cannot be overridden by local configuration, by default.</p><p>The bootstrap context uses a different convention for locating
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external configuration than the main application context, so instead
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of <code class="literal">application.yml</code> (or <code class="literal">.properties</code>) you use <code class="literal">bootstrap.yml</code>,
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keeping the external configuration for bootstrap and main context
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nicely separate. Example:</p><p><b>bootstrap.yml. </b>
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</p><pre class="screen">spring:
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application:
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name: foo
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cloud:
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config:
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uri: ${SPRING_CONFIG_URI:http://localhost:8888}</pre><p>
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</p><p>It is a good idea to set the <code class="literal">spring.application.name</code> (in
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<code class="literal">bootstrap.yml</code> or <code class="literal">application.yml</code>) if your application needs any
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application-specific configuration from the server.</p><p>You can disable the bootstrap process completely by setting
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<code class="literal">spring.cloud.bootstrap.enabled=false</code> (e.g. 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
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<code class="literal">SpringApplicationBuilder</code>, then the Bootstrap context is added as a
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parent to that context. It is a feature of Spring that child contexts
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inherit property sources and profiles from their parent, so the "main"
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application context will contain additional property sources, compared
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to building the same context without Spring Cloud Config. The
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additional property sources are:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">"bootstrap": an optional <code class="literal">CompositePropertySource</code> appears with high
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priority if any <code class="literal">PropertySourceLocators</code> are found in the Bootstrap
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context, and they have non-empty properties. An example would be
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properties from the Spring Cloud Config Server. See
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<a class="link" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-property-sources" title="1.6 Customizing the Bootstrap Property Sources">below</a> for instructions
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on how to customize the contents of this property source.</li><li class="listitem">"applicationConfig: [classpath:bootstrap.yml]" (and friends if
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Spring profiles are active). If you have a <code class="literal">bootstrap.yml</code> (or
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properties) then those properties are used to configure the Bootstrap
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context, and then they get added to the child context when its parent
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is set. They have lower precedence than the <code class="literal">application.yml</code> (or
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properties) and any other property sources that are added to the child
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as a normal part of the process of creating a Spring Boot
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application. See <a class="link" href="multi__spring_cloud_context_application_context_services.html#customizing-bootstrap-properties" title="1.3 Changing the Location of Bootstrap Properties">below</a> for
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instructions on how to customize the contents of these property
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sources.</li></ul></div><p>Because of the ordering rules of property sources the "bootstrap"
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entries take precedence, but note that these do not contain any data
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from <code class="literal">bootstrap.yml</code>, which has very low precedence, but can be used
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to set defaults.</p><p>You can extend the context hierarchy by simply setting the parent
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context of any <code class="literal">ApplicationContext</code> you create, e.g. using its own
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interface, or with the <code class="literal">SpringApplicationBuilder</code> convenience methods
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(<code class="literal">parent()</code>, <code class="literal">child()</code> and <code class="literal">sibling()</code>). The bootstrap context will be
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the parent of the most senior ancestor that you create yourself.
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Every context in the hierarchy will have its own "bootstrap" property
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source (possibly empty) to avoid promoting values inadvertently from
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parents down to their descendants. Every context in the hierarchy can
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also (in principle) have a different <code class="literal">spring.application.name</code> and
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hence a different remote property source if there is a Config
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Server. Normal Spring application context behaviour rules apply to
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property resolution: properties from a child context override those in
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the parent, by name and also by property source name (if the child has
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a property source with the same name as the parent, the one from the
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parent is not included in the child).</p><p>Note that the <code class="literal">SpringApplicationBuilder</code> allows you to share an
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<code class="literal">Environment</code> amongst the whole hierarchy, but that is not the
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default. Thus, sibling contexts in particular do not need to have the
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same profiles or property sources, even though they will share common
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things with their parent.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="customizing-bootstrap-properties" href="#customizing-bootstrap-properties"></a>1.3 Changing the Location of Bootstrap Properties</h2></div></div></div><p>The <code class="literal">bootstrap.yml</code> (or <code class="literal">.properties</code>) location can be specified using
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<code class="literal">spring.cloud.bootstrap.name</code> (default "bootstrap") or
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<code class="literal">spring.cloud.bootstrap.location</code> (default empty), e.g. in System
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properties. Those properties behave like the <code class="literal">spring.config.*</code>
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variants with the same name, in fact they are used to set up the
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bootstrap <code class="literal">ApplicationContext</code> by setting those properties in its
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<code class="literal">Environment</code>. If there is an active profile (from
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<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) then properties in that profile will be
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loaded as well, just like in a regular Spring Boot app, e.g. from
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<code class="literal">bootstrap-development.properties</code> for a "development" 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 you application by the
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bootstrap context are often "remote" (e.g. from a Config Server), and
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by default they cannot be overridden locally, except on the command
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line. If you want to allow your applications to override the remote
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properties with their own System properties or config files, the
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remote property source has to grant it permission by setting
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<code class="literal">spring.cloud.config.allowOverride=true</code> (it doesn’t work to set this
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locally). Once that flag is set there are some finer grained settings
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to control the location of the remote properties in relation to System
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properties and the application’s local configuration:
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<code class="literal">spring.cloud.config.overrideNone=true</code> to override with any local
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property source, and
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<code class="literal">spring.cloud.config.overrideSystemProperties=false</code> if only System
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properties and env vars should override the remote settings, but not
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the local config files.</p></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 trained to do anything you like by adding
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entries to <code class="literal">/META-INF/spring.factories</code> under the key
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<code class="literal">org.springframework.cloud.bootstrap.BootstrapConfiguration</code>. This is
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a comma-separated list of Spring <code class="literal">@Configuration</code> classes which will
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be used to create the context. Any beans that you want to be available
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to the main application context for autowiring can be created here,
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and also there is a special contract for <code class="literal">@Beans</code> of type
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<code class="literal">ApplicationContextInitializer</code>. Classes can be marked with an <code class="literal">@Order</code>
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if you want to control the startup sequence (the default order is
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"last").</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>Be careful when adding custom <code class="literal">BootstrapConfiguration</code> that the
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classes you add are not <code class="literal">@ComponentScanned</code> by mistake into your
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"main" application context, where they might not be needed.
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Use a separate package name for boot configuration classes that is
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not already covered by your <code class="literal">@ComponentScan</code> or <code class="literal">@SpringBootApplication</code>
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annotated configuration classes.</p></td></tr></table></div><p>The bootstrap process ends by injecting initializers into the main
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<code class="literal">SpringApplication</code> instance (i.e. the normal Spring Boot startup
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sequence, whether it is running as a standalone app or deployed in an
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application server). First a bootstrap context is created from the
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classes found in <code class="literal">spring.factories</code> and then all <code class="literal">@Beans</code> of type
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<code class="literal">ApplicationContextInitializer</code> are added to the main
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<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
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bootstrap process is the Config Server, but you can add additional
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sources by adding beans of type <code class="literal">PropertySourceLocator</code> to the
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bootstrap context (via <code class="literal">spring.factories</code>). You could use this to
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insert additional properties from a different server, or from a
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database, for instance.</p><p>As an example, consider the following trivial custom locator:</p><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@Configuration</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">class</span> CustomPropertySourceLocator <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">implements</span> PropertySourceLocator {
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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> PropertySource<?> locate(Environment environment) {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> MapPropertySource(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"customProperty"</span>,
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Collections.<String, Object>singletonMap(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"property.from.sample.custom.source"</span>, <span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"worked as intended"</span>));
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}
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}</pre><p>The <code class="literal">Environment</code> that is passed in is the one for the
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<code class="literal">ApplicationContext</code> about to be created, i.e. the one that we are
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supplying additional property sources for. It will already have its
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normal Spring Boot-provided property sources, so you can use those to
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locate a property source specific to this <code class="literal">Environment</code> (e.g. by
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keying it on the <code class="literal">spring.application.name</code>, as is done in the default
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Config Server property source locator).</p><p>If you create a jar with this class in it and then add a
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<code class="literal">META-INF/spring.factories</code> containing:</p><pre class="screen">org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator</pre><p>then the "customProperty" <code class="literal">PropertySource</code> will show up in any
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application that includes that jar on its classpath.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_environment_changes" href="#_environment_changes"></a>1.7 Environment Changes</h2></div></div></div><p>The application will listen for an <code class="literal">EnvironmentChangeEvent</code> and react
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to the change in a couple of standard ways (additional
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<code class="literal">ApplicationListeners</code> can be added as <code class="literal">@Beans</code> by the user in the
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normal way). When an <code class="literal">EnvironmentChangeEvent</code> is observed it will
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have a list of key values that have changed, and the application will
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use those to:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">Re-bind any <code class="literal">@ConfigurationProperties</code> beans in the context</li><li class="listitem">Set the logger levels for any properties in <code class="literal">logging.level.*</code></li></ul></div><p>Note that the Config Client does not by default poll for changes in
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the <code class="literal">Environment</code>, and generally we would not recommend that approach
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for detecting changes (although you could set it up with a
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<code class="literal">@Scheduled</code> annotation). If you have a scaled-out client application
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then it is better to broadcast the <code class="literal">EnvironmentChangeEvent</code> to all
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the instances instead of having them polling for changes (e.g. using
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the <a class="link" href="https://github.com/spring-cloud/spring-cloud-bus" target="_top">Spring Cloud
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Bus</a>).</p><p>The <code class="literal">EnvironmentChangeEvent</code> covers a large class of refresh use
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cases, as long as you can actually make a change to the <code class="literal">Environment</code>
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and publish the event (those APIs are public and part of core
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Spring). You can verify the changes are bound to
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<code class="literal">@ConfigurationProperties</code> beans by visiting the <code class="literal">/configprops</code>
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endpoint (normal Spring Boot Actuator feature). For instance a
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<code class="literal">DataSource</code> can have its <code class="literal">maxPoolSize</code> changed at runtime (the
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default <code class="literal">DataSource</code> created by Spring Boot is an
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<code class="literal">@ConfigurationProperties</code> bean) and grow capacity
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dynamically. Re-binding <code class="literal">@ConfigurationProperties</code> does not cover
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another large class of use cases, where you need more control over the
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refresh, and where you need a change to be atomic over the whole
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<code class="literal">ApplicationContext</code>. To address those concerns we have
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<code class="literal">@RefreshScope</code>.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_refresh_scope" href="#_refresh_scope"></a>1.8 Refresh Scope</h2></div></div></div><p>A Spring <code class="literal">@Bean</code> that is marked as <code class="literal">@RefreshScope</code> will get special
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treatment when there is a configuration change. This addresses the
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problem of stateful beans that only get their configuration injected
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when they are initialized. For instance if a <code class="literal">DataSource</code> has open
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connections when the database URL is changed via the <code class="literal">Environment</code>, we
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probably want the holders of those connections to be able to complete
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what they are doing. Then the next time someone borrows a connection
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from the pool he gets one with the new URL.</p><p>Refresh scope beans are lazy proxies that initialize when they are
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used (i.e. when a method is called), and the scope acts as a cache of
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initialized values. To force a bean to re-initialize on the next
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method call you just need to invalidate its cache entry.</p><p>The <code class="literal">RefreshScope</code> is a bean in the context and it has a public method
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<code class="literal">refreshAll()</code> to refresh all beans in the scope by clearing the
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target cache. There is also a <code class="literal">refresh(String)</code> method to refresh an
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individual bean by name. This functionality is exposed in the
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<code class="literal">/refresh</code> endpoint (over HTTP or JMX).</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p><code class="literal">@RefreshScope</code> works (technically) on an <code class="literal">@Configuration</code>
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class, but it might lead to surprising behaviour: e.g. it does <span class="strong"><strong>not</strong></span>
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mean that all the <code class="literal">@Beans</code> defined in that class are themselves
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<code class="literal">@RefreshScope</code>. Specifically, anything that depends on those beans
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cannot rely on them being updated when a refresh is initiated, unless
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it is itself in <code class="literal">@RefreshScope</code> (in which it will be rebuilt on a
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refresh and its dependencies re-injected, at which point they will be
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re-initialized from the refreshed <code class="literal">@Configuration</code>).</p></td></tr></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_encryption_and_decryption" href="#_encryption_and_decryption"></a>1.9 Encryption and Decryption</h2></div></div></div><p>Spring Cloud has an <code class="literal">Environment</code> pre-processor for decrypting
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property values locally. It follows the same rules as the Config
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Server, and has the same external configuration via <code class="literal">encrypt.*</code>. Thus
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you can use encrypted values in the form <code class="literal">{cipher}*</code> and as long as
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there is a valid key then they will be decrypted before the main
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application context gets the <code class="literal">Environment</code>. To use the encryption
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features in an application you need to include Spring Security RSA in
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your classpath (Maven co-ordinates
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"org.springframework.security:spring-security-rsa") and you also need
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the full strength JCE extensions in your JVM.</p><p>If you are getting an exception due to "Illegal key size" and you are using Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html" target="_top">Java 6 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html" target="_top">Java 7 JCE</a></li><li class="listitem"><a class="link" href="http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html" target="_top">Java 8 JCE</a></li></ul></div><p>Extract files into JDK/jre/lib/security folder (whichever version of JRE/JDK x64/x86 you are using).</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_endpoints" href="#_endpoints"></a>1.10 Endpoints</h2></div></div></div><p>For a Spring Boot Actuator application there are some additional management endpoints:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">POST to <code class="literal">/env</code> to update the <code class="literal">Environment</code> and rebind <code class="literal">@ConfigurationProperties</code> and log levels</li><li class="listitem"><code class="literal">/refresh</code> for re-loading the boot strap context and refreshing the <code class="literal">@RefreshScope</code> beans</li><li class="listitem"><code class="literal">/restart</code> for closing the <code class="literal">ApplicationContext</code> and restarting it (disabled by default)</li><li class="listitem"><code class="literal">/pause</code> and <code class="literal">/resume</code> for calling the <code class="literal">Lifecycle</code> methods (<code class="literal">stop()</code> and <code class="literal">start()</code> on the <code class="literal">ApplicationContext</code>)</li></ul></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi_pr01.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="multi__spring_cloud_commons_common_abstractions.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-commons.html">Home</a></td><td width="40%" align="right" valign="top"> 2. Spring Cloud Commons: Common Abstractions</td></tr></table></div></body></html>
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