# Spring Cloud Circuit Breaker

## 1. Usage Documentation

The Spring Cloud CircuitBreaker project contains implementations for Resilience4J and Spring Retry.
The APIs implemented in Spring Cloud CircuitBreaker live in Spring Cloud Commons. The usage documentation
for these APIs are located in the [Spring Cloud Commons documentation](https://docs.spring.io/spring-cloud-commons/docs/current/reference/html/#spring-cloud-circuit-breaker).

### 1.1. Configuring Resilience4J Circuit Breakers

#### 1.1.1. Starters

There are two starters for the Resilience4J implementations, one for reactive applications and one for non-reactive applications.

* `org.springframework.cloud:spring-cloud-starter-circuitbreaker-resilience4j` - non-reactive applications

* `org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j` - reactive applications

#### 1.1.2. Auto-Configuration

You can disable the Resilience4J auto-configuration by setting`spring.cloud.circuitbreaker.resilience4j.enabled` to `false`.

#### 1.1.3. Default Configuration

To provide a default configuration for all of your circuit breakers create a `Customize` bean that is passed a`Resilience4JCircuitBreakerFactory` or `ReactiveResilience4JCircuitBreakerFactory`.
The `configureDefault` method can be used to provide a default configuration.

```
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> defaultCustomizer() {
    return factory -> factory.configureDefault(id -> new Resilience4JConfigBuilder(id)
            .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(4)).build())
            .circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
            .build());
}
```

##### Reactive Example

```
@Bean
public Customizer<ReactiveResilience4JCircuitBreakerFactory> defaultCustomizer() {
    return factory -> factory.configureDefault(id -> new Resilience4JConfigBuilder(id)
            .circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
            .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(4)).build()).build());
}
```

#### 1.1.4. Specific Circuit Breaker Configuration

Similarly to providing a default configuration, you can create a `Customize` bean this is passed a`Resilience4JCircuitBreakerFactory` or `ReactiveResilience4JCircuitBreakerFactory`.

```
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> slowCustomizer() {
    return factory -> factory.configure(builder -> builder.circuitBreakerConfig(CircuitBreakerConfig.ofDefaults())
            .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(2)).build()), "slow");
}
```

In addition to configuring the circuit breaker that is created you can also customize the circuit breaker after it has been created but before it is returned to the caller.
To do this you can use the `addCircuitBreakerCustomizer`method.
This can be useful for adding event handlers to Resilience4J circuit breakers.

```
@Bean
public Customizer<Resilience4JCircuitBreakerFactory> slowCustomizer() {
    return factory -> factory.addCircuitBreakerCustomizer(circuitBreaker -> circuitBreaker.getEventPublisher()
    .onError(normalFluxErrorConsumer).onSuccess(normalFluxSuccessConsumer), "normalflux");
}
```

##### Reactive Example

```
@Bean
public Customizer<ReactiveResilience4JCircuitBreakerFactory> slowCustomizer() {
    return factory -> {
        factory.configure(builder -> builder
        .timeLimiterConfig(TimeLimiterConfig.custom().timeoutDuration(Duration.ofSeconds(2)).build())
        .circuitBreakerConfig(CircuitBreakerConfig.ofDefaults()), "slow", "slowflux");
        factory.addCircuitBreakerCustomizer(circuitBreaker -> circuitBreaker.getEventPublisher()
            .onError(normalFluxErrorConsumer).onSuccess(normalFluxSuccessConsumer), "normalflux");
     };
}
```

#### 1.1.5. Circuit Breaker Properties Configuration

You can configure `CircuitBreaker` and `TimeLimiter` instances in your application’s configuration properties file.
Property configuration has higher priority than Java `Customizer` configuration.

```
resilience4j.circuitbreaker:
 instances:
     backendA:
         registerHealthIndicator: true
         slidingWindowSize: 100
     backendB:
         registerHealthIndicator: true
         slidingWindowSize: 10
         permittedNumberOfCallsInHalfOpenState: 3
         slidingWindowType: TIME_BASED
         recordFailurePredicate: io.github.robwin.exception.RecordFailurePredicate

resilience4j.timelimiter:
 instances:
     backendA:
         timeoutDuration: 2s
         cancelRunningFuture: true
     backendB:
         timeoutDuration: 1s
         cancelRunningFuture: false
```

For more information on Resilience4j property configuration, see [Resilience4J Spring Boot 2 Configuration](https://resilience4j.readme.io/docs/getting-started-3#configuration).

#### 1.1.6. Bulkhead pattern supporting

If `resilience4j-bulkhead` is on the classpath, Spring Cloud CircuitBreaker will wrap all methods with a Resilience4j Bulkhead.
You can disable the Resilience4j Bulkhead by setting `spring.cloud.circuitbreaker.bulkhead.resilience4j.enabled` to `false`.

Spring Cloud CircuitBreaker Resilience4j provides two implementation of bulkhead pattern:

* a `SemaphoreBulkhead` which uses Semaphores

* a `FixedThreadPoolBulkhead` which uses a bounded queue and a fixed thread pool.

By default, Spring Cloud CircuitBreaker Resilience4j uses `FixedThreadPoolBulkhead`. For more information on implementation
of Bulkhead patterns see the [Resilience4j Bulkhead](https://resilience4j.readme.io/docs/bulkhead).

The `Customizer<Resilience4jBulkheadProvider>` can be used to provide a default `Bulkhead` and `ThreadPoolBulkhead` configuration.

```
@Bean
public Customizer<Resilience4jBulkheadProvider> defaultBulkheadCustomizer() {
    return provider -> provider.configureDefault(id -> new Resilience4jBulkheadConfigurationBuilder()
        .bulkheadConfig(BulkheadConfig.custom().maxConcurrentCalls(4).build())
        .threadPoolBulkheadConfig(ThreadPoolBulkheadConfig.custom().coreThreadPoolSize(1).maxThreadPoolSize(1).build())
        .build()
);
}
```

#### 1.1.7. Specific Bulkhead Configuration

Similarly to proving a default 'Bulkhead' or 'ThreadPoolBulkhead' configuration, you can create a `Customize` bean this
is passed a `Resilience4jBulkheadProvider`.

```
@Bean
public Customizer<Resilience4jBulkheadProvider> slowBulkheadProviderCustomizer() {
    return provider -> provider.configure(builder -> builder
        .bulkheadConfig(BulkheadConfig.custom().maxConcurrentCalls(1).build())
        .threadPoolBulkheadConfig(ThreadPoolBulkheadConfig.ofDefaults()), "slowBulkhead");
}
```

In addition to configuring the Bulkhead that is created you can also customize the bulkhead and thread pool bulkhead after they
have been created but before they are returned to caller. To do this you can use the `addBulkheadCustomizer` and `addThreadPoolBulkheadCustomizer`methods.

##### Bulkhead Example

```
@Bean
public Customizer<Resilience4jBulkheadProvider> customizer() {
    return provider -> provider.addBulkheadCustomizer(bulkhead -> bulkhead.getEventPublisher()
        .onCallRejected(slowRejectedConsumer)
        .onCallFinished(slowFinishedConsumer), "slowBulkhead");
}
```

##### Thread Pool Bulkhead Example

```
@Bean
public Customizer<Resilience4jBulkheadProvider> slowThreadPoolBulkheadCustomizer() {
    return provider -> provider.addThreadPoolBulkheadCustomizer(threadPoolBulkhead -> threadPoolBulkhead.getEventPublisher()
        .onCallRejected(slowThreadPoolRejectedConsumer)
        .onCallFinished(slowThreadPoolFinishedConsumer), "slowThreadPoolBulkhead");
}
```

#### 1.1.8. Bulkhead Properties Configuration

You can configure ThreadPoolBulkhead and SemaphoreBulkhead instances in your application’s configuration properties file.
Property configuration has higher priority than Java `Customizer` configuration.

```
resilience4j.thread-pool-bulkhead:
    instances:
        backendA:
            maxThreadPoolSize: 1
            coreThreadPoolSize: 1
resilience4j.bulkhead:
    instances:
        backendB:
            maxConcurrentCalls: 10
```

For more inforamtion on the Resilience4j property configuration, see [Resilience4J Spring Boot 2 Configuration](https://resilience4j.readme.io/docs/getting-started-3#configuration).

#### 1.1.9. Collecting Metrics

Spring Cloud Circuit Breaker Resilience4j includes auto-configuration to setup metrics collection as long as the right
dependencies are on the classpath. To enable metric collection you must include `org.springframework.boot:spring-boot-starter-actuator`, and `io.github.resilience4j:resilience4j-micrometer`. For more information on the metrics that
get produced when these dependencies are present, see the [Resilience4j documentation](https://resilience4j.readme.io/docs/micrometer).

|   |You don’t have to include `micrometer-core` directly as it is brought in by `spring-boot-starter-actuator`|
|---|----------------------------------------------------------------------------------------------------------|

### 1.2. Configuring Spring Retry Circuit Breakers

Spring Retry provides declarative retry support for Spring applications.
A subset of the project includes the ability to implement circuit breaker functionality.
Spring Retry provides a circuit breaker implementation via a combination of it’s[`CircuitBreakerRetryPolicy`](https://github.com/spring-projects/spring-retry/blob/master/src/main/java/org/springframework/retry/policy/CircuitBreakerRetryPolicy.java)and a [stateful retry](https://github.com/spring-projects/spring-retry#stateful-retry).
All circuit breakers created using Spring Retry will be created using the `CircuitBreakerRetryPolicy` and a[`DefaultRetryState`](https://github.com/spring-projects/spring-retry/blob/master/src/main/java/org/springframework/retry/support/DefaultRetryState.java).
Both of these classes can be configured using `SpringRetryConfigBuilder`.

#### 1.2.1. Default Configuration

To provide a default configuration for all of your circuit breakers create a `Customize` bean that is passed a`SpringRetryCircuitBreakerFactory`.
The `configureDefault` method can be used to provide a default configuration.

```
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> defaultCustomizer() {
    return factory -> factory.configureDefault(id -> new SpringRetryConfigBuilder(id)
        .retryPolicy(new TimeoutRetryPolicy()).build());
}
```

#### 1.2.2. Specific Circuit Breaker Configuration

Similarly to providing a default configuration, you can create a `Customize` bean this is passed a`SpringRetryCircuitBreakerFactory`.

```
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> slowCustomizer() {
    return factory -> factory.configure(builder -> builder.retryPolicy(new SimpleRetryPolicy(1)).build(), "slow");
}
```

In addition to configuring the circuit breaker that is created you can also customize the circuit breaker after it has been created but before it is returned to the caller.
To do this you can use the `addRetryTemplateCustomizers`method.
This can be useful for adding event handlers to the `RetryTemplate`.

```
@Bean
public Customizer<SpringRetryCircuitBreakerFactory> slowCustomizer() {
    return factory -> factory.addRetryTemplateCustomizers(retryTemplate -> retryTemplate.registerListener(new RetryListener() {

        @Override
        public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) {
            return false;
        }

        @Override
        public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {

        }

        @Override
        public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {

        }
    }));
}
```

## 2. Building

### 2.1. Basic Compile and Test

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
```

|   |You can also install Maven (\>=3.3.3) yourself and run the `mvn` command<br/>in place of `./mvnw` in the examples below. If you do that you also<br/>might need to add `-P spring` if your local Maven settings do not<br/>contain repository declarations for spring pre-release artifacts.|
|---|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   |Be aware that you might need to increase the amount of memory<br/>available to Maven by setting a `MAVEN_OPTS` environment variable with<br/>a value like `-Xmx512m -XX:MaxPermSize=128m`. We try to cover this in<br/>the `.mvn` configuration, so if you find you have to do it to make a<br/>build succeed, please raise a ticket to get the settings added to<br/>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](https://www.docker.com/get-started)) is installed and running.

### 2.2. Documentation

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 `${main.basedir}`(defaults to `$/tmp/releaser-1645116950347-0/spring-cloud-circuitbreaker/docs`, 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.

### 2.3. Working with the code

If you don’t have an IDE preference we would recommend that you use[Spring Tools Suite](https://www.springsource.com/developer/sts) or[Eclipse](https://eclipse.org) when working with the code. We use the[m2eclipse](https://eclipse.org/m2e/) 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.

#### 2.3.1. Activate the Spring Maven profile

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.

#### 2.3.2. Importing into eclipse with m2eclipse

We recommend the [m2eclipse](https://eclipse.org/m2e/) eclipse plugin when working with
eclipse. If you don’t already have m2eclipse installed it is available from the "eclipse
marketplace".

|   |Older versions of m2e do not support Maven 3.3, so once the<br/>projects are imported into Eclipse you will also need to tell<br/>m2eclipse to use the right profile for the projects. If you<br/>see many different errors related to the POMs in the projects, check<br/>that you have an up to date installation. If you can’t upgrade m2e,<br/>add the "spring" profile to your `settings.xml`. Alternatively you can<br/>copy the repository settings from the "spring" profile of the parent<br/>pom into your `settings.xml`.|
|---| |

#### 2.3.3. Importing into eclipse without m2eclipse

If you prefer not to use m2eclipse you can generate eclipse project metadata using the
following command:

```
$ ./mvnw eclipse:eclipse
```

The generated eclipse projects can be imported by selecting `import existing projects`from the `file` menu.

## 3. Contributing

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.

### 3.1. Sign the Contributor License Agreement

Before we accept a non-trivial patch or pull request we will need you to sign the[Contributor License Agreement](https://cla.pivotal.io/sign/spring).
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.

### 3.2. Code of Conduct

This project adheres to the Contributor Covenant [code of
conduct](https://github.com/spring-cloud/spring-cloud-build/blob/master/docs/src/main/asciidoc/code-of-conduct.adoc). By participating, you are expected to uphold this code. Please report
unacceptable behavior to [[email protected]](/cdn-cgi/l/email-protection#4c3f3c3e25222b612f23282961232a612f232228392f380c3c253a23382d20622523).

### 3.3. Code Conventions and Housekeeping

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.xml` file from the[Spring
  Cloud Build](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-dependencies-parent/eclipse-code-formatter.xml) project. If using IntelliJ, you can use the[Eclipse Code Formatter
  Plugin](https://plugins.jetbrains.com/plugin/6546) to import the same file.

* Make sure all new `.java` files to have a simple Javadoc class comment with at least an`@author` tag identifying you, and preferably at least a paragraph on what the class is
  for.

* Add the ASF license header comment to all new `.java` files (copy from existing files
  in the project)

* Add yourself as an `@author` to 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](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html),
  if you are fixing an existing issue please add `Fixes gh-XXXX` at the end of the commit
  message (where XXXX is the issue number).

### 3.4. Checkstyle

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:

spring-cloud-build-tools/

```
└── src
    ├── checkstyle
    │   └── checkstyle-suppressions.xml (3)
    └── main
        └── resources
            ├── checkstyle-header.txt (2)
            └── checkstyle.xml (1)
```

|**1**|Default Checkstyle rules |
|-----|-------------------------|
|**2**|    File header setup    |
|**3**|Default suppression rules|

#### 3.4.1. Checkstyle configuration

Checkstyle rules are **disabled by default**. To add checkstyle to your project just define the following properties and plugins.

pom.xml

```
<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>
```

|**1**|                                    Fails the build upon Checkstyle errors                                    |
|-----|--------------------------------------------------------------------------------------------------------------|
|**2**|                                  Fails the build upon Checkstyle violations                                  |
|**3**|                                  Checkstyle analyzes also the test sources                                   |
|**4**|Add the Spring Java Format plugin that will reformat your code to pass most of the Checkstyle formatting rules|
|**5**|                           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:

projectRoot/src/checkstyle/checkstyle-suppresions.xml

```
<?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 .springformat
```

### 3.5. IDE setup

#### 3.5.1. Intellij IDEA

In 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](https://github.com/spring-cloud/spring-cloud-build/tree/master/spring-cloud-build-tools) project.

spring-cloud-build-tools/

```
└── 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)
```

|**1**|                         Default Checkstyle rules                         |
|-----|--------------------------------------------------------------------------|
|**2**|                            File header setup                             |
|**3**|                        Default suppression rules                         |
|**4**|    Project defaults for Intellij that apply most of Checkstyle rules     |
|**5**|Project style conventions for Intellij that apply most of Checkstyle rules|

![Code style](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-code-style.png)

Figure 1. Code style

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.

![Code style](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-inspections.png)

Figure 2. Inspection profiles

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.

Checkstyle

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

![Checkstyle](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/docs/src/main/asciidoc/images/intellij-checkstyle.png)

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](https://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.txt` file either in your cloned repo or via the `[raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle-header.txt](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/main/resources/checkstyle-header.txt)` URL.

* `checkstyle.suppressions.file` - default suppressions. Please point it to the Spring Cloud Build’s, `spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xml` file either in your cloned repo or via the `[raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xml](https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-build-tools/src/checkstyle/checkstyle-suppressions.xml)` URL.

* `checkstyle.additional.suppressions.file` - this variable corresponds to suppressions in your local project. E.g. you’re working on `spring-cloud-contract`. Then point to the `project-root/src/checkstyle/checkstyle-suppressions.xml` folder. Example for `spring-cloud-contract` would be: `/home/username/spring-cloud-contract/src/checkstyle/checkstyle-suppressions.xml`.

|   |Remember to set the `Scan Scope` to `All sources` since we apply checkstyle rules for production and test sources.|
|---|------------------------------------------------------------------------------------------------------------------|

### 3.6. Duplicate Finder

Spring Cloud Build brings along the `basepom:duplicate-finder-maven-plugin`, that enables flagging duplicate and conflicting classes and resources on the java classpath.

#### 3.6.1. Duplicate Finder configuration

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`.

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](https://github.com/basepom/duplicate-finder-maven-plugin/wiki).

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>
```

