Reuseable code across microservices in JAVA
- Mark Kendall
- Feb 11
- 3 min read
In the Java/Spring Boot world, the equivalent to other frameworks for reusable code across microservices is a shared library (JAR file). Here's a breakdown of how to create and use them, along with best practices:
1. Creating the Shared Library (JAR):
*Project Setup:** Create a new Java project (you can use Maven or Gradle). This project will house your reusable code. It should not be a Spring Boot application itself, just a plain Java library. This keeps it lightweight and avoids unnecessary dependencies in your microservices.
*Code Organization:** Organize your code into packages based on functionality. This improves readability and maintainability.
*Dependencies:** Declare any external library dependencies your shared code relies on in your `pom.xml` (Maven) or `build.gradle` (Gradle).
*Building the JAR:** Use your build tool (Maven or Gradle) to build the project. This will create a JAR file containing your compiled code. The command will typically be `mvn clean package` (Maven) or `./gradlew clean build` (Gradle).
*Example (Maven `pom.xml` snippet):**
```xml
<project>
<groupId>com.example</groupId>
<artifactId>shared-utils</artifactId>
<version>1.0.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.12.0</version>
</dependency>
</dependencies>
</project>
```
2. Using the Shared Library in Microservices:
*Dependency Management:** In each microservice's `pom.xml` or `build.gradle`, add the shared library as a dependency. You'll need to specify the `groupId`, `artifactId`, and `version` of your shared library.
*Example (Maven `pom.xml` in a microservice):**
```xml
<dependency>
<groupId>com.example</groupId>
<artifactId>shared-utils</artifactId>
<version>1.0.0-SNAPSHOT</version>
</dependency>
```
*Repository:** For your microservices to find the shared library, you'll need a repository. Here are the common options:
*Local Maven Repository:** For development, you can install the JAR to your local Maven repository (`mvn install`). This isn't ideal for production.
*Centralized Repository (Nexus, Artifactory, etc.):** This is the recommended approach for production. These repositories allow you to manage and version your shared libraries. You deploy the JAR to the repository, and your microservices can then pull it from there.
*Direct JAR Inclusion (Less Common):** You can include the JAR directly in your microservice's `lib` folder. This is generally discouraged due to versioning issues and difficulty managing dependencies.
*Usage:** Once the dependency is added, you can import and use the classes from your shared library in your microservice code just like any other library.
3. Best Practices:
*Versioning:** Use semantic versioning (e.g., 1.0.0, 1.0.1, 2.0.0) for your shared library. This helps microservices manage updates and avoid breaking changes.
*Backward Compatibility:** Strive for backward compatibility when making changes to your shared library. Avoid changing or removing methods that are already in use.
*Testing:** Thoroughly test your shared library independently. This ensures that it works correctly and doesn't introduce bugs into your microservices.
*Documentation:** Document your shared library well. This makes it easier for other developers to understand and use it.
*Minimize Dependencies:** Keep the dependencies of your shared library to a minimum. This reduces the risk of dependency conflicts in your microservices.
*Avoid Spring Boot in the Library (Usually):** As mentioned earlier, generally, keep the shared library a plain Java library. Including Spring Boot in the shared library can lead to dependency conflicts and unnecessary overhead in the microservices. If you absolutely need Spring components in the shared library, be very careful with version compatibility and consider the implications.
*Consider a Build System (Maven or Gradle):** Using a build system is essential for managing dependencies, building JARs, and deploying them to repositories.
Example Code (Conceptual):
Shared Library (shared-utils):
```java
package com.example.utils;
public class StringUtils {
public static String capitalize(String str) {
if (str == null || str.isEmpty()) {
return str;
}
return str.substring(0, 1).toUpperCase() + str.substring(1);
}
}
```
Microservice:
```java
package com.example.microservice;
import com.example.utils.StringUtils; // Import from the shared library
public class MyService {
public void doSomething(String name) {
String capitalizedName = StringUtils.capitalize(name);
System.out.println("Capitalized name: " + capitalizedName);
}
}
```
By following these steps, you can create and use shared libraries effectively in your Spring Boot microservice architecture, promoting code reuse and simplifying development. Remember to choose the repository solution that best fits your needs. Centralized repositories are strongly recommended for production environments.
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