Scenario:
A developer complains that their code compiles fine on their local machine but fails on the build server. What could be the issue, and how would you resolve this?

1. Understand the Problem

When code compiles on one machine but fails on another, it usually points to differences in the development environment. Here are the most common causes:

2. Common Causes

a. Java Version Mismatch:

• The local machine and build server might be using different versions of the JDK.
• Example: Local machine uses Java 11, but the build server uses Java 8.

b. Missing Dependencies:

• The build server might be missing libraries or dependencies required for compilation.

c. Environment Variables:

• Differences in environment variables (e.g., JAVA_HOME, CLASSPATH) can cause issues.

d. Build Tool Configuration:

• Maven, Gradle, or Ant configurations might differ between the local machine and the build server.

e. File Encoding:

• Differences in file encoding (e.g., UTF-8 vs. ASCII) can cause compilation errors.

3. Troubleshooting Steps

Step 1: Check Java Version
Ensure both machines are using the same JDK version.

Command to Check Java Version:

java -version

Example Output:

openjdk version "11.0.12" 2023-07-18

Solution:

• Install the same JDK version on the build server.
• Update the build tool configuration to use the correct JDK version.

Step 2: Verify Dependencies
Ensure all required libraries and dependencies are available on the build server.

For Maven:

• Check the pom.xml file for dependencies.
• Run mvn clean install to download dependencies.

For Gradle:

• Check the build.gradle file for dependencies.
• Run gradle build to download dependencies.

Step 3: Check Environment Variables
Ensure environment variables like JAVA_HOME and CLASSPATH are correctly set on the build server.

Command to Check JAVA_HOME:

echo $JAVA_HOME

Example Output:

/usr/lib/jvm/java-11-openjdk

Solution:

• Set JAVA_HOME to the correct JDK path on the build server.

Step 4: Compare Build Tool Configurations
Ensure the build tool configurations (e.g., pom.xml, build.gradle) are identical on both machines.

Example Maven pom.xml:

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>my-app</artifactId>
    <version>1.0-SNAPSHOT</version>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

Solution:

• Sync the build tool configurations between the local machine and the build server.

Step 5: Check File Encoding
Ensure all source files use the same encoding (e.g., UTF-8).

For Maven:
Add the following to your pom.xml:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

Add the following to your build.gradle:

tasks.withType(JavaCompile) {
    options.encoding = 'UTF-8'
}

4. Example Scenario

Local Machine:

• Java 11 is installed.
• Maven is configured to use Java 11.
• All dependencies are downloaded.

Build Server:

• Java 8 is installed.
• Maven is configured to use Java 8.
• Some dependencies are missing.

Error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project my-app: Compilation failure
[ERROR] /path/to/MyClass.java:[10,20] cannot find symbol
[ERROR]   symbol:   variable someLibrary
[ERROR]   location: class MyClass

Solution:

1. Install Java 11 on the build server.
2. Update JAVA_HOME to point to Java 11.
3. Run mvn clean install to download missing dependencies.

Summary

To resolve compilation issues between local and build servers:

1. Check and match the Java version.
2. Verify and sync dependencies.
3. Ensure environment variables are correctly set.
4. Compare and align build tool configurations.
5. Use consistent file encoding.