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[#25] Added Javadocs and documentation for dependencies

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This commit is contained in:
Marcin Grzejszczak
2015-08-15 22:09:25 +02:00
parent 8c3ee16fff
commit c57f4b53c7
20 changed files with 250 additions and 80 deletions
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189
docs/src/main/asciidoc/spring-cloud-zookeeper.adoc
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@@ -79,6 +79,195 @@ public String serviceUrl() {
}
----
[[spring-cloud-zookeeper-dependencies]]
=== Using the Zookeeper Dependencies
Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application as properties. As dependencies you can understand other applications that are registered
in Zookeeper and which you would like to call via https://github.com/spring-cloud/spring-cloud-netflix/blob/master/docs/src/main/asciidoc/spring-cloud-netflix.adoc#spring-cloud-feign[Feign] (a REST client builder)
and also https://github.com/spring-cloud/spring-cloud-netflix/blob/master/docs/src/main/asciidoc/spring-cloud-netflix.adoc#spring-cloud-ribbon[Spring `RestTemplate`].
You can also benefit from the Zookeeper Dependency Watchers functionality that lets you control and monitor what is the state of your dependencies and decide what to do with that.
=== How to activate Zookeeper Dependencies
- Including a dependency on `org.springframework.cloud:spring-cloud-starter-zookeeper-discovery` will enable auto-configuration that will setup Spring Cloud Zookeeper Dependencies.
- In addition to that you have to set the property `spring.cloud.zookeeper.dependencies.enabled` to true (defaults to `true` if not set explicitly).
- You have to have the `spring.cloud.zookeeper.dependencies` section properly set up - check the subsequent section for more details.
=== Setting up Zookeeper Dependencies
Let's take a closer look at an example of dependencies representation:
.application.yml
----
spring.application.name: yourServiceName
spring.cloud.zookeeper:
dependencies:
newsletter:
path: /path/where/newsletter/has/registered/in/zookeeper
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.newsletter.$version+json
version: v1
headers:
header1:
- value1
header2:
- value2
required: false
mailing:
path: /path/where/mailing/has/registered/in/zookeeper
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.mailing.$version+json
version: v1
required: true
----
Let's now go through each part of the dependency one by one. The root property name is `spring.cloud.zookeeper.dependencies`.
==== Aliases
Below the root property you have to represent each dependency has by an alias due to the constraints of Ribbon (the application id has to be placed in the URL
thus you can't pass any complex path like /foo/bar/name). The alias will be the name that you will use instead of serviceId for `DiscoveryClient`, `Feign` or `RestTemplate`.
In the aforementioned examples the aliases are `newsletter` and `mailing`. Example of Feign usage with `newsletter` would be:
----
@FeignClient("newsletter")
public interface NewsletterService {
@RequestMapping(method = RequestMethod.GET, value = "/newsletter")
String getNewsletters();
}
----
==== Path
Represented by `path` yaml property.
Path is the path under which the dependency is registered under Zookeeper. Like presented before Ribbon operates on URLs thus this path is not compliant with its requirement.
That is why Spring Cloud Zookeeper maps the alias to the proper path.
==== Load balancer type
Represented by `loadBalancerType` yaml property.
If you know what kind of load balancing strategy has to be applied when calling this particular dependency then you can provide it in the yaml file and it will be automatically applied.
You can choose one of the following load balancing strategies
- STICKY - once chosen the instance will always be called
- RANDOM - picks an instance randomly
- ROUND_ROBIN - iterates over instances over and over again
==== Content-Type template and version
Represented by `contentTypeTemplate` and `version` yaml property.
If you version your api via the `Content-Type` header then you don't want to add this header to each of your requests. Also if you want to call a new version of the API you don't want to
roam around your code to bump up the API version. That's why you can provide a `contentTypeTemplate` with a special `$version` placeholder. That placeholder will be filled by the value of the
`version` yaml property. Let's take a look at an example.
Having the following `contentTypeTemplate`:
----
application/vnd.newsletter.$version+json
----
and the following `version`:
----
v1
----
Will result in setting up of a `Content-Type` header for each request:
----
application/vnd.newsletter.v1+json
----
==== Default headers
Represented by `headers` map in yaml
Sometimes each call to a dependency requires setting up of some default headers. In order not to do that in code you can set them up in the yaml file.
Having the following `headers` section:
----
headers:
Accept:
- text/html
- application/xhtml+xml
Cache-Control:
- no-cache
----
Results in adding the `Accept` and `Cache-Control` headers with appropriate list of values in your HTTP request.
==== Obligatory dependencies
Represented by `required` property in yaml
If one of your dependencies is required to be up and running when your application is booting then it's enough to set up the `required: true` property in the yaml file.
If your application can't localize the required dependency during boot time it will throw an exception and the Spring Context will fail to set up.
In other words your application won't be able to start if the required dependency is not registered in Zookeeper.
You can read more about Spring Cloud Zookeeper Presence Checker in the following sections.
=== Configuring Spring Cloud Zookeeper Dependencies
There is a bunch of properties that you can set to enable / disable parts of Zookeeper Dependencies functionalities.
- `spring.cloud.zookeeper.dependencies` - if you don't set this property you won't benefit from Zookeeper Dependencies
- `spring.cloud.zookeeper.dependencies.ribbon.enabled` (enabled by default) - Ribbon requires explicit global configuration or a particular one for a dependency. By turning on this property
runtime load balancing strategy resolution is possible and you can profit from the `loadBalancerType` section of the Zookeeper Dependencies. The configuration that needs this property
has an implementation of `LoadBalancerClient` that delegates to the `ILoadBalancer` presented in the next bullet
- `spring.cloud.zookeeper.dependencies.ribbon.loadbalancer` (enabled by default) - thanks to this property the custom `ILoadBalancer` knows that the part of the URI passed to Ribbon might
actually be the alias that has to be resolved to a proper path in Zookeeper. Without this property you won't be able to register applications under nested paths.
- `spring.cloud.zookeeper.dependencies.headers.enabled` (enabled by default) - this property registers such a `RibbonClient` that automatically will append appropriate headers and content
types with version as presented in the Dependency configuration. Without this setting of those two parameters will not be operational.
- `spring.cloud.zookeeper.dependencies.resttemplate.enabled` (enabled by default) - when enabled will modify the request headers of `@LoadBalanced` annotated `RestTemplate` so that it passes
headers and content type with version set in Dependency configuration. Wihtout this setting of those two parameters will not be operational.
[[spring-cloud-zookeeper-dependency-watcher]]
=== Spring Cloud Zookeeper Dependency Watcher
The Dependency Watcher mechanism allows you to register listeners to your dependencies. The functionality is in fact an implementation of the `Observator` pattern. When a dependency changes
its state (UP or DOWN) then some custom logic can be applied.
=== How to activate
Spring Cloud Zookeeper Dependencies functionality needs to be enabled to profit from Dependency Watcher mechanism.
=== Registering a listener
In order to register a listener you have to implement an interface `org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener` and register it as a bean.
The interface gives you one method:
----
/**
* Method executed upon state change of a dependency
*
* @param dependencyName - alias from microservice configuration {@see ZookeeperDependencies}
* @param newState
*/
void stateChanged(String dependencyName, DependencyState newState);
----
If you want to register a listener for a particular dependency then the `dependencyName` would be the discriminator for your concrete implementation. `newState` will provide you with information
whether your dependency has changed to `CONNECTED` or `DISCONNECTED`.
=== Presence Checker
Bound with Dependency Watcher is the functionality called Presence Checker. It allows you to provide custom behaviour upon booting of your application to react accordingly to the state
of your dependencies.
The default implementation of the abstract `org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier` class is the
`org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier` which works in the following way.
- If the dependency is marked us `required` and it's not in Zookeeper then upon booting your application will throw an exception and shutdown
- If dependency is not `required` the `org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker` will log that application is missing at `WARN` level
The functionality can be overriden since the `DefaultDependencyPresenceOnStartupVerifier` is registered only when there is no bean of `DependencyPresenceOnStartupVerifier`.
[[spring-cloud-zookeeper-config]]
== Distributed Configuration with Zookeeper

7
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/dependency/DependenciesBasedLoadBalancer.java
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@@ -16,7 +16,12 @@
package org.springframework.cloud.zookeeper.discovery.dependency;
import com.netflix.loadbalancer.*;
import com.netflix.loadbalancer.BaseLoadBalancer;
import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import com.netflix.loadbalancer.RoundRobinRule;
import com.netflix.loadbalancer.Server;
import com.netflix.loadbalancer.ServerList;
import lombok.extern.slf4j.Slf4j;
import java.util.Map;

3
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/dependency/DependenciesPassedCondition.java
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@@ -24,6 +24,9 @@ import org.springframework.core.type.AnnotatedTypeMetadata;
import java.util.Map;
/**
* Condition that verifies if the Dependencies have been passed in an appropriate
* place in the application properties.
*
* @author Marcin Grzejszczak, 4financeIT
*/
public class DependenciesPassedCondition extends SpringBootCondition {

2
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/dependency/DependencyRestTemplateAutoConfiguration.java
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@@ -21,6 +21,7 @@ import com.google.common.collect.Maps;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.zookeeper.discovery.ConditionalOnRibbonZookeeper;
import org.springframework.context.annotation.Configuration;
@@ -47,6 +48,7 @@ import java.util.Map;
@ConditionalOnRibbonZookeeper
@Configuration
@ConditionalOnDependenciesPassed
@ConditionalOnProperty(value = "spring.cloud.zookeeper.dependencies.resttemplate.enabled", matchIfMissing = true)
@Slf4j
public class DependencyRestTemplateAutoConfiguration {

13
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/dependency/LoadBalancerType.java
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@@ -21,17 +21,4 @@ package org.springframework.cloud.zookeeper.discovery.dependency;
*/
public enum LoadBalancerType {
STICKY, RANDOM, ROUND_ROBIN;
public static LoadBalancerType fromName(String strategyName) {
if (strategyName == null) {
return ROUND_ROBIN;
}
for (LoadBalancerType type : values()) {
if (type.name().equals(strategyName.toUpperCase())) {
return type;
}
}
return ROUND_ROBIN;
}
}

5
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/dependency/ZookeeperDependencies.java
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@@ -22,7 +22,10 @@ import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.util.StringUtils;
import javax.annotation.PostConstruct;
import java.util.*;
import java.util.Collection;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import static java.util.Collections.singletonList;

16
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/DefaultDependencyWatcher.java
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@@ -15,11 +15,6 @@
*/
package org.springframework.cloud.zookeeper.discovery.watcher;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import lombok.SneakyThrows;
import org.apache.curator.x.discovery.ServiceCache;
import org.springframework.cloud.client.discovery.event.InstanceRegisteredEvent;
@@ -29,7 +24,18 @@ import org.springframework.cloud.zookeeper.discovery.dependency.ZookeeperDepende
import org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier;
import org.springframework.context.ApplicationListener;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/**
* This Dependency Watcher will verify the presence of dependencies upon startup and registers listeners
* to changing of state of dependencies during the application's lifecycle.
*
* @see DependencyPresenceOnStartupVerifier
* @see DependencyWatcherListener
*
* @author Marcin Grzejszczak, 4financeIT
* @author Michal Chmielarz, 4financeIT
*/

3
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/DependencyRegistrationHookProvider.java
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@@ -18,6 +18,9 @@ package org.springframework.cloud.zookeeper.discovery.watcher;
import java.io.IOException;
/**
* Implementations of this interface are required to register dependency registration hooks
* on startup and their cleaning upon application context shutdown.
*
* @author <a href="http://www.4financeit.com>4financeIT</a>
*/
public interface DependencyRegistrationHookProvider {

3
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/DependencyState.java
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@@ -16,6 +16,9 @@
package org.springframework.cloud.zookeeper.discovery.watcher;
/**
*
* Represents a dependency's Zookeeper connection state
*
* @author <a href="http://www.4financeit.com>4financeIT</a>
*/
public enum DependencyState {

3
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/DependencyStateChangeListenerRegistry.java
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@@ -25,6 +25,9 @@ import org.slf4j.LoggerFactory;
import java.util.List;
/**
*
* Informs all the DependencyWatcherListeners that a dependency's state has changed
*
* @author Marcin Grzejszczak, 4financeIT
* @author Tomasz Nurkiewicz, 4financeIT
*/

50
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/DependencyWatcher.java
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@@ -1,50 +0,0 @@
/*
* Copyright 2013-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.cloud.zookeeper.discovery.watcher;
import java.io.IOException;
public interface DependencyWatcher {
/**
* Register hooks upon dependencies registration
*
* @throws Exception
*/
void registerDependencyRegistrationHooks() throws Exception;
/**
* Unregister hooks upon dependencies registration
*
* @throws IOException
*/
void clearDependencyRegistrationHooks() throws IOException;
/**
* Register a listener for a dependency
*
* @param listener
*/
void registerDependencyStateChangeListener(DependencyWatcherListener listener);
/**
* Unregister a listener for a dependency
*
* @param listener
*/
void clearDependencyStateChangeListener(DependencyWatcherListener listener);
}

5
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/presence/DefaultDependencyPresenceOnStartupVerifier.java
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@@ -16,6 +16,11 @@
package org.springframework.cloud.zookeeper.discovery.watcher.presence;
/**
* By default passes logging dependency checker in order not to shutdown the application
* if dependency is missing
*
* @see LogMissingDependencyChecker
*
* @author <a href="http://www.4financeit.com>4financeIT</a>
*/
public class DefaultDependencyPresenceOnStartupVerifier extends DependencyPresenceOnStartupVerifier {

9
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/presence/DependencyPresenceOnStartupVerifier.java
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@@ -18,6 +18,15 @@ package org.springframework.cloud.zookeeper.discovery.watcher.presence;
import org.apache.curator.x.discovery.ServiceCache;
/**
*
* Verifier that checks for presence of mandatory dependencies and delegates to an optional
* presence checker verification of presence of optional dependencies.
*
* The default implementation of required dependencies will result in shutting down of the application
* if the dependency is missing.
*
* @see FailOnMissingDependencyChecker
*
* @author Marcin Grzejszczak, 4financeIT
* @author Tomasz Szymanski, 4financeIT
*/

5
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/presence/FailOnMissingDependencyChecker.java
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@@ -16,12 +16,13 @@
package org.springframework.cloud.zookeeper.discovery.watcher.presence;
import org.apache.curator.x.discovery.ServiceInstance;
import org.springframework.cloud.zookeeper.discovery.watcher.presence.NoInstancesRunningException;
import org.springframework.cloud.zookeeper.discovery.watcher.presence.PresenceChecker;
import java.util.List;
/**
*
* Will result in throwing an exception if there are no running instances of the dependency
*
* @author Marcin Grzejszczak, 4financeIT
* @author Adam Chudzik, 4financeIT
*/

5
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/presence/LogMissingDependencyChecker.java
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@@ -23,6 +23,9 @@ import java.lang.invoke.MethodHandles;
import java.util.List;
/**
*
* Will log the missing microservice dependency
*
* @author Marcin Grzejszczak, 4financeIT
* @author Tomasz Dziurko, 4financeIT
*/
@@ -33,7 +36,7 @@ public class LogMissingDependencyChecker implements PresenceChecker {
@Override
public void checkPresence(String dependencyName, List<ServiceInstance> serviceInstances) {
if (serviceInstances.isEmpty()) {
log.warn("Microservice dependency with name [" + dependencyName + "] is missing.");
log.warn("Microservice dependency with name [{}] is missing.", dependencyName);
}
}

3
spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/watcher/presence/PresenceChecker.java
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@@ -20,6 +20,9 @@ import org.apache.curator.x.discovery.ServiceInstance;
import java.util.List;
/**
* The implementation of this interface will be called upon checking if a dependency with a given name
* is present upon startup within the provided service instances.
*
* @author <a href="http://www.4financeit.com>4financeIT</a>
*/
public interface PresenceChecker {

2
spring-cloud-zookeeper-discovery/src/test/groovy/org/springframework/cloud/zookeeper/discovery/PollingUtils.groovy
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@@ -24,7 +24,7 @@ trait PollingUtils {
} catch (Exception e) {
AssertionError assertionError = new AssertionError("Exception occurred while evaluating closure", e)
System.err.println(assertionError)
return assertionError
throw assertionError
}
}
}

4
spring-cloud-zookeeper-discovery/src/test/resources/application-dependencies.yml
View File

@@ -2,7 +2,6 @@ spring.application.name: nameWithoutAlias
spring.cloud.zookeeper:
dependencies:
someAlias:
id: someId
path: nameWithoutAlias
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.newsletter.$version+json
@@ -14,9 +13,8 @@ spring.cloud.zookeeper:
- value2
required: false
testInstance2:
id: someId2
path: somePath2
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.newsletter.$version+json2
contentTypeTemplate: application/vnd.newsletter.$version+json
version: v1
required: false

1
spring-cloud-zookeeper-discovery/src/test/resources/application-loadbalancerclient.yml
View File

@@ -2,6 +2,5 @@ spring.application.name: loadbalancerclient
spring.cloud.zookeeper:
dependencies:
someAlias:
id: someId
path: testInstance
loadBalancerType: STICKY

2
spring-cloud-zookeeper-discovery/src/test/resources/application-watcher.yml
View File

@@ -2,7 +2,6 @@ spring.application.name: some/name/without/alias
spring.cloud.zookeeper:
dependencies:
someAlias:
id: someId
path: testInstance
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.newsletter.$version+json
@@ -14,7 +13,6 @@ spring.cloud.zookeeper:
- value2
required: false
testInstance2:
id: someId2
path: somePath2
loadBalancerType: ROUND_ROBIN
contentTypeTemplate: application/vnd.newsletter.$version+json2