This project provides Zookeeper integrations for Spring Boot applications through autoconfiguration and binding to the Spring Environment and other Spring programming model idioms. With a few annotations, you can quickly enable and configure the common patterns inside your application and build large distributed systems with Zookeeper based components. The provided patterns include Service Discovery and Configuration. The project also provides client-side load-balancing via integration with Spring Cloud LoadBalancer.
This quick start walks through using Spring Cloud Zookeeper for Service Discovery and Distributed Configuration.
First, run Zookeeper on your machine. Then you can access it and use it as a Service Registry and Configuration source with Spring Cloud Zookeeper.
To use these features in an application, you can build it as a Spring Boot application that depends on spring-cloud-zookeeper-core and spring-cloud-zookeeper-discovery.
The most convenient way to add the dependency is with a Spring Boot starter: org.springframework.cloud:spring-cloud-starter-zookeeper-discovery.
We recommend using dependency management and spring-boot-starter-parent.
The following example shows a typical Maven configuration:
<project>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>{spring-boot-version}</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-zookeeper-discovery</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>The following example shows a typical Gradle setup:
plugins {
id 'org.springframework.boot' version ${spring-boot-version}
id 'io.spring.dependency-management' version ${spring-dependency-management-version}
id 'java'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.cloud:spring-cloud-starter-zookeeper-discovery'
testImplementation 'org.springframework.boot:spring-boot-starter-test'
}
dependencyManagement {
imports {
mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
}
}|
Warning
|
Depending on the version you are using, you might need to adjust Apache Zookeeper version used in your project. You can read more about it in the Install Zookeeper section. |
Now you can create a standard Spring Boot application, such as the following HTTP server:
@SpringBootApplication
@RestController
public class Application {
@GetMapping("/")
public String home() {
return "Hello World!";
}
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
When this HTTP server runs, it connects to Zookeeper, which runs on the default local port (2181).
To modify the startup behavior, you can change the location of Zookeeper by using application.properties, as shown in the following example:
spring:
cloud:
zookeeper:
connect-string: localhost:2181
You can now use DiscoveryClient, @LoadBalanced RestTemplate, or @LoadBalanced WebClient.Builder to retrieve services and instances data from Zookeeper, as shown in the following example:
@Autowired
private DiscoveryClient discoveryClient;
public String serviceUrl() {
List<ServiceInstance> list = discoveryClient.getInstances("STORES");
if (list != null && list.size() > 0 ) {
return list.get(0).getUri().toString();
}
return null;
}To use these features in an application, you can build it as a Spring Boot application that depends on spring-cloud-zookeeper-core and spring-cloud-zookeeper-config.
The most convenient way to add the dependency is with a Spring Boot starter: org.springframework.cloud:spring-cloud-starter-zookeeper-config.
We recommend using dependency management and spring-boot-starter-parent.
The following example shows a typical Maven configuration:
<project>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>{spring-boot-version}</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-zookeeper-config</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>The following example shows a typical Gradle setup:
plugins {
id 'org.springframework.boot' version ${spring-boot-version}
id 'io.spring.dependency-management' version ${spring-dependency-management-version}
id 'java'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'org.springframework.cloud:spring-cloud-starter-zookeeper-config'
testImplementation 'org.springframework.boot:spring-boot-starter-test'
}
dependencyManagement {
imports {
mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
}
}|
Warning
|
Depending on the version you are using, you might need to adjust Apache Zookeeper version used in your project. You can read more about it in the Install Zookeeper section. |
Now you can create a standard Spring Boot application, such as the following HTTP server:
@SpringBootApplication
@RestController
public class Application {
@GetMapping("/")
public String home() {
return "Hello World!";
}
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
The application retrieves configuration data from Zookeeper.
|
Warning
|
If you use Spring Cloud Zookeeper Config, you need to set the spring.config.import property in order to bind to Zookeeper.
You can read more about it in the Spring Boot Config Data Import section.
|
ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services. See the Zookeeper site for more information. Spring Cloud Zookeeper also builds on the Apache Curator project, which started life at Netflix.
Spring Cloud Zookeeper includes the following features:
-
Spring Cloud
DiscoveryClientimplementation (supports Spring Cloud LoadBalancer) -
Zookeeper-based
PropertySourceloaded during the 'bootstrap' phase
-
Install zookeeper (On a mac with homebrew, use
brew install zookeeper). -
Run
mvn --settings .settings.xml package. Doing so brings in the required Spring Cloud Maven repositories and Build. -
Run
java -jar spring-cloud-zookeeper-sample/target/spring-cloud-zookeeper-sample-1.2.0.BUILD-SNAPSHOT.jar. -
Visit localhost:8080 to verify that
{"serviceId":"testZookeeperApp","host":"<yourhost>","port":8080}works. -
Run
java -jar spring-cloud-zookeeper-sample/target/spring-cloud-zookeeper-sample-1.2.0.BUILD-SNAPSHOT.jar --server.port=8081 -
Visit localhost:8080 again to verify that
{"serviceId":"testZookeeperApp","host":"<yourhost>","port":8081}eventually shows up in the results in a round-robin fashion. (It may take a minute or so.)
To build the source you will need to install JDK 17.
Spring Cloud uses Maven for most build-related activities, and you should be able to get off the ground quite quickly by cloning the project you are interested in and typing
$ ./mvnw install
|
Note
|
You can also install Maven (>=3.3.3) yourself and run the mvn command
in place of ./mvnw in the examples below. If you do that you also
might need to add -P spring if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.
|
|
Note
|
Be aware that you might need to increase the amount of memory
available to Maven by setting a MAVEN_OPTS environment variable with
a value like -Xmx512m -XX:MaxPermSize=128m. We try to cover this in
the .mvn configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.
|
The projects that require middleware (i.e. Redis) for testing generally require that a local instance of [Docker](www.docker.com/get-started) is installed and running.
The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources from
src/main/asciidoc. As part of that process it will look for a
README.adoc and process it by loading all the includes, but not
parsing or rendering it, just copying it to ${main.basedir}
(defaults to ${basedir}, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.
If you don’t have an IDE preference we would recommend that you use Spring Tools Suite or Eclipse when working with the code. We use the m2eclipse eclipse plugin for maven support. Other IDEs and tools should also work without issue as long as they use Maven 3.3.3 or better.
Spring Cloud projects require the 'spring' Maven profile to be activated to resolve the spring milestone and snapshot repositories. Use your preferred IDE to set this profile to be active, or you may experience build errors.
We recommend the m2eclipse eclipse plugin when working with eclipse. If you don’t already have m2eclipse installed it is available from the "eclipse marketplace".
|
Note
|
Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects. If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation. If you can’t upgrade m2e,
add the "spring" profile to your settings.xml. Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your settings.xml.
|
Spring Cloud is released under the non-restrictive Apache 2.0 license, and follows a very standard Github development process, using Github tracker for issues and merging pull requests into master. If you want to contribute even something trivial please do not hesitate, but follow the guidelines below.
Before we accept a non-trivial patch or pull request we will need you to sign the Contributor License Agreement. Signing the contributor’s agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do. Active contributors might be asked to join the core team, and given the ability to merge pull requests.
This project adheres to the Contributor Covenant code of conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to spring-code-of-conduct@pivotal.io.
None of these is essential for a pull request, but they will all help. They can also be added after the original pull request but before a merge.
-
Use the Spring Framework code format conventions. If you use Eclipse you can import formatter settings using the
eclipse-code-formatter.xmlfile from the Spring Cloud Build project. If using IntelliJ, you can use the Eclipse Code Formatter Plugin to import the same file. -
Make sure all new
.javafiles to have a simple Javadoc class comment with at least an@authortag identifying you, and preferably at least a paragraph on what the class is for. -
Add the ASF license header comment to all new
.javafiles (copy from existing files in the project) -
Add yourself as an
@authorto the .java files that you modify substantially (more than cosmetic changes). -
Add some Javadocs and, if you change the namespace, some XSD doc elements.
-
A few unit tests would help a lot as well — someone has to do it.
-
If no-one else is using your branch, please rebase it against the current master (or other target branch in the main project).
-
When writing a commit message please follow these conventions, if you are fixing an existing issue please add
Fixes gh-XXXXat the end of the commit message (where XXXX is the issue number).
Spring Cloud Build comes with a set of checkstyle rules. You can find them in the spring-cloud-build-tools module. The most notable files under the module are:
└── src ├── checkstyle │ └── checkstyle-suppressions.xml (3) └── main └── resources ├── checkstyle-header.txt (2) └── checkstyle.xml (1)
-
Default Checkstyle rules
-
File header setup
-
Default suppression rules
Checkstyle rules are disabled by default. To add checkstyle to your project just define the following properties and plugins.
<properties>
<maven-checkstyle-plugin.failsOnError>true</maven-checkstyle-plugin.failsOnError> (1)
<maven-checkstyle-plugin.failsOnViolation>true
</maven-checkstyle-plugin.failsOnViolation> (2)
<maven-checkstyle-plugin.includeTestSourceDirectory>true
</maven-checkstyle-plugin.includeTestSourceDirectory> (3)
</properties>
<build>
<plugins>
<plugin> (4)
<groupId>io.spring.javaformat</groupId>
<artifactId>spring-javaformat-maven-plugin</artifactId>
</plugin>
<plugin> (5)
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
</plugin>
</plugins>
<reporting>
<plugins>
<plugin> (5)
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-checkstyle-plugin</artifactId>
</plugin>
</plugins>
</reporting>
</build>
-
Fails the build upon Checkstyle errors
-
Fails the build upon Checkstyle violations
-
Checkstyle analyzes also the test sources
-
Add the Spring Java Format plugin that will reformat your code to pass most of the Checkstyle formatting rules
-
Add checkstyle plugin to your build and reporting phases
If you need to suppress some rules (e.g. line length needs to be longer), then it’s enough for you to define a file under ${project.root}/src/checkstyle/checkstyle-suppressions.xml with your suppressions. Example:
<?xml version="1.0"?>
<!DOCTYPE suppressions PUBLIC
"-//Puppy Crawl//DTD Suppressions 1.1//EN"
"https://www.puppycrawl.com/dtds/suppressions_1_1.dtd">
<suppressions>
<suppress files=".*ConfigServerApplication\.java" checks="HideUtilityClassConstructor"/>
<suppress files=".*ConfigClientWatch\.java" checks="LineLengthCheck"/>
</suppressions>
It’s advisable to copy the ${spring-cloud-build.rootFolder}/.editorconfig and ${spring-cloud-build.rootFolder}/.springformat to your project. That way, some default formatting rules will be applied. You can do so by running this script:
$ curl https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/.editorconfig -o .editorconfig
$ touch .springformatIn order to setup Intellij you should import our coding conventions, inspection profiles and set up the checkstyle plugin. The following files can be found in the Spring Cloud Build project.
└── src ├── checkstyle │ └── checkstyle-suppressions.xml (3) └── main └── resources ├── checkstyle-header.txt (2) ├── checkstyle.xml (1) └── intellij ├── Intellij_Project_Defaults.xml (4) └── Intellij_Spring_Boot_Java_Conventions.xml (5)
-
Default Checkstyle rules
-
File header setup
-
Default suppression rules
-
Project defaults for Intellij that apply most of Checkstyle rules
-
Project style conventions for Intellij that apply most of Checkstyle rules
Go to File → Settings → Editor → Code style. There click on the icon next to the Scheme section. There, click on the Import Scheme value and pick the Intellij IDEA code style XML option. Import the spring-cloud-build-tools/src/main/resources/intellij/Intellij_Spring_Boot_Java_Conventions.xml file.
Go to File → Settings → Editor → Inspections. There click on the icon next to the Profile section. There, click on the Import Profile and import the spring-cloud-build-tools/src/main/resources/intellij/Intellij_Project_Defaults.xml file.
To have Intellij work with Checkstyle, you have to install the Checkstyle plugin. It’s advisable to also install the Assertions2Assertj to automatically convert the JUnit assertions
Go to File → Settings → Other settings → Checkstyle. There click on the + icon in the Configuration file section. There, you’ll have to define where the checkstyle rules should be picked from. In the image above, we’ve picked the rules from the cloned Spring Cloud Build repository. However, you can point to the Spring Cloud Build’s GitHub repository (e.g. for the checkstyle.xml : raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle.xml). We need to provide the following variables:
-
checkstyle.header.file- please point it to the Spring Cloud Build’s,spring-cloud-build-tools/src/main/resources/checkstyle-header.txtfile either in your cloned repo or via theraw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle-header.txtURL. -
checkstyle.suppressions.file- default suppressions. Please point it to the Spring Cloud Build’s,spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xmlfile either in your cloned repo or via theraw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xmlURL. -
checkstyle.additional.suppressions.file- this variable corresponds to suppressions in your local project. E.g. you’re working onspring-cloud-contract. Then point to theproject-root/src/checkstyle/checkstyle-suppressions.xmlfolder. Example forspring-cloud-contractwould be:/home/username/spring-cloud-contract/src/checkstyle/checkstyle-suppressions.xml.
|
Important
|
Remember to set the Scan Scope to All sources since we apply checkstyle rules for production and test sources.
|
Spring Cloud Build brings along the basepom:duplicate-finder-maven-plugin, that enables flagging duplicate and conflicting classes and resources on the java classpath.
Duplicate finder is enabled by default and will run in the verify phase of your Maven build, but it will only take effect in your project if you add the duplicate-finder-maven-plugin to the build section of the projecst’s pom.xml.
<build>
<plugins>
<plugin>
<groupId>org.basepom.maven</groupId>
<artifactId>duplicate-finder-maven-plugin</artifactId>
</plugin>
</plugins>
</build>For other properties, we have set defaults as listed in the plugin documentation.
You can easily override them but setting the value of the selected property prefixed with duplicate-finder-maven-plugin. For example, set duplicate-finder-maven-plugin.skip to true in order to skip duplicates check in your build.
If you need to add ignoredClassPatterns or ignoredResourcePatterns to your setup, make sure to add them in the plugin configuration section of your project:
<build>
<plugins>
<plugin>
<groupId>org.basepom.maven</groupId>
<artifactId>duplicate-finder-maven-plugin</artifactId>
<configuration>
<ignoredClassPatterns>
<ignoredClassPattern>org.joda.time.base.BaseDateTime</ignoredClassPattern>
<ignoredClassPattern>.*module-info</ignoredClassPattern>
</ignoredClassPatterns>
<ignoredResourcePatterns>
<ignoredResourcePattern>changelog.txt</ignoredResourcePattern>
</ignoredResourcePatterns>
</configuration>
</plugin>
</plugins>
</build>