## Spring Cloud Sleuth

Spring Cloud Sleuth provides Spring Boot auto-configuration for distributed tracing.

Sleuth configures everything you need to get started. This includes where trace data (spans) are reported to, how many traces to keep (sampling), if remote fields (baggage) are sent, and which libraries are traced.

### Quick Start

Add Spring Cloud Sleuth to the classpath of a Spring Boot application (together with a Tracer implementation) and you will see trace IDs in logs. Example of Sleuth with Brave tracer:

    <!-- Spring Cloud Sleuth requires a Spring Cloud BOM -->
    <dependencyManagement>
    	<dependencies>
    		<dependency>
    			<groupId>org.springframework.cloud</groupId>
    			<artifactId>spring-cloud-dependencies</artifactId>
    			<!-- Provide the latest stable Spring Cloud release train version (e.g. 2020.0.0) -->
    			<version>${release.train.version}</version>
    			<type>pom</type>
    			<scope>import</scope>
    		</dependency>
    	</dependencies>
    </dependencyManagement>

    <dependencies>
    	<!-- Boot's Web support -->
    	<dependency>
    		<groupId>org.springframework.boot</groupId>
    		<artifactId>spring-boot-starter-web</artifactId>
    	</dependency>
    	<!-- Sleuth with Brave tracer implementation -->
    	<dependency>
    		<groupId>org.springframework.cloud</groupId>
    		<artifactId>spring-cloud-starter-sleuth</artifactId>
    	</dependency>
    </dependencies>

Consider the following HTTP handler:

    @RestController
    public class DemoController {
    	private static Logger log = LoggerFactory.getLogger(DemoController.class);

    	@RequestMapping("/")
    	public String home() {
    		log.info("Handling home");
    		return "Hello World";
    	}
    }

If you add that handler to a controller, you can see the calls to `home()` being traced in the logs (notice the `0b6aaf642574edd3` ids).

    2020-10-21 12:01:16.285  INFO [,0b6aaf642574edd3,0b6aaf642574edd3,true] 289589 --- [nio-9000-exec-1] DemoController	          : Handling home!

| Instead of logging the request in the handler explicitly, you could set `logging.level.org.springframework.web.servlet.DispatcherServlet=DEBUG`.

| Set `spring.application.name=myService` (for instance) to see the service name as well as the trace and span IDs.

## Documentation

Please visit the documentation page to read more about the project.

## Building

### Basic Compile and Test

To build the source you will need to install JDK 1.8.

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 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.

| 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](https://www.docker.com/get-started) is installed and running.

### 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-1634698077973-0/spring-cloud-sleuth/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.

### Working with the code

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.

#### 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.

#### Importing into eclipse with m2eclipse

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".

| 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`.

#### 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.

## 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.

### 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. 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.

### Code of Conduct

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.

### 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 project. If using IntelliJ, you can use the Eclipse Code Formatter Plugin 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, 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).

### 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

#### 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

### IDE setup

#### 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 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

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.

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

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` : `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 `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 `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.