[Solved] java: log cannot be resolved – Java

The Problem:

A developer is using IntelliJ IDEA with lombok and slf4j for logging in their Java code. When they try to build the code, they get the error message "Error:(16, 10) java: log cannot be resolved." Despite enabling annotation processing and configuring the necessary dependencies in the project’s pom.xml file, the issue persists. What could be the reason for the error and how can it be resolved?

The Solutions:

Solution 1: Maven Update

To resolve the issue of "log cannot be resolved" in Java, try the following steps:

1. Open your project’s root directory in a command line window.

2. Run the following command to perform a Maven update:

   mvn clean install -U

   This command will clean the project, install all dependencies, and update them to the latest versions.

3. After the update is complete, run your application using the following command:

   mvn spring-boot:run

By updating the dependencies, you ensure that you are using the latest versions of the libraries, which may address the issue of "log cannot be resolved".

Solution 2: Install Lombok Plugin

To resolve the "log cannot be resolved" issue, you may need to install the Lombok Plugin. This plugin provides IDEA with the necessary understanding of the @Slf4j annotation and enables it to recognize and work with the lombok library effectively.

Steps to install the Lombok Plugin:

1. Open IntelliJ IDEA and navigate to the “Settings” or “Preferences” dialog (depending on your operating system).
2. Locate the “Plugins” section and click on the “Browse repositories…” button.
3. In the search field, enter “Lombok Plugin” and press “Enter” to search for the plugin.
4. Once you find the “Lombok Plugin,” click on the “Install” button to begin the installation process.
5. Follow the on-screen instructions to complete the installation.
6. Restart IntelliJ IDEA to ensure that the plugin is properly loaded and integrated.

After installing the Lombok Plugin, IntelliJ IDEA should be able to resolve the "log" variable and recognize the @Slf4j annotation correctly, allowing you to use the lombok library effectively in your Java project.

Solution 3: Enable annotation processing

To resolve the issue “log cannot be resolved,” follow these steps:

1. Install Lombok Plugin: Ensure you have the Lombok Plugin installed in IntelliJ IDEA. It allows you to use annotations like @Slf4j in your code.
2. Enable Annotation Processing: Navigate to Settings > Build, Execution, Deployment > Compiler > Annotation Processors. Enable the option Enable annotation processing.
3. Rebuild Project: After making these changes, do a Build > Rebuild Project to update the project configuration and resolve the issue.

By following these steps, you can successfully use Lombok annotations like @Slf4j in your project.

Solution 4: Change compiler to Javac

In some cases, the “log cannot be resolved” error may be due to an incorrect compiler configuration in your IDE. To fix this, you can change the compiler to Java Compiler (Javac) instead of the default Ajc compiler. Here are the steps:

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1. Open your IDE’s settings or preferences dialog. The exact steps may vary depending on your IDE, but generally, you can find the settings under the “File” or “Settings” menu.
2. Navigate to the section that controls the compiler settings. This may be called “Compiler” or “Java Compiler”.
3. In the compiler settings, look for an option to select the compiler type. This may be labeled “Compiler” or “Java Compiler”.
4. Select “Javac” as the compiler.
5. Save your changes and restart your IDE if prompted.

After changing the compiler to Javac, try compiling your code again. The "log cannot be resolved" error should now be resolved.

Solution 5: Renamed log variable via lombok.config

It is possible that you have a lombok.config file that renames the log variable to something else using the lombok.log.fieldName = xxx setting. Check if you have such a file and if so, make sure that the new variable name is used instead of log.