Скачать или смотреть Resolving the Issue of Servlets Initialized Multiple Times in Tomcat with Java 9

Discover the solution to the problem of servlets being initialized multiple times in Tomcat when upgrading to Java 9. Learn how to configure your Tomcat server to prevent this issue.
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Resolving the Issue of Servlets Initialized Multiple Times in Tomcat with Java 9

If you've recently upgraded your web application to use Java 9 and noticed that your servlets are getting initialized multiple times, you're not alone. This behavior can result in duplicated resources, such as logs and temporary files, which can complicate your website's operation. In this guide, we will dive into the problem and provide a solution to ensure your servlet behaves as expected.

Understanding the Problem

When deploying an application on Tomcat, servlets are expected to initialize once for each defined context. However, after upgrading from Java 8 to Java 9, it's been reported that servlets are initialized multiple times. Here’s how the issue manifests:

First Initialization: The servlet initializes correctly with the expected ServletConfig.

Subsequent Initializations: Each virtual directory or subfolder leads to additional, unintended initializations of the servlet.

What Does This Mean?

This means that the method init(ServletConfig) is executed for each context defined in your application, leading to:

Duplication of temporary files and logs.

Increased resource consumption and potential performance impacts.

Example Scenario

Consider this configuration in your server.xml, which sets up a Tomcat Host:

[[See Video to Reveal this Text or Code Snippet]]

In this configuration:

The Host points to a base directory containing multiple subfolders.

Each folder appears to trigger a new servlet initialization.

The Solution

The solution to this problem has been identified as modifying configuration settings in your server.xml file. Follow the steps below:

Open the server.xml File:

Locate the server.xml file in your Tomcat configuration directory.

Modify Host Configuration:

Change the autoDeploy and deployOnStartup attributes in the Host definition:

[[See Video to Reveal this Text or Code Snippet]]

Save Changes:

After making the changes, save the file and restart your Tomcat server.

Key Attributes Explained:

autoDeploy: Setting this to false prevents Tomcat from automatically deploying changes in the web application's context.

deployOnStartup: This setting determines if contexts will be deployed when the server starts. By disabling it, you regain control over the deployment of your servlets.

Benefits of the Solution:

Prevention of Duplicate Initialization: This configuration eliminates extra calls to the init(ServletConfig) method, ensuring your servlets are initialized only once.

Streamlined Logging: Avoid multiple logs scattered across your application directories.

Conclusion

Upgrading to a new Java version can introduce unforeseen issues, such as servlets being initialized multiple times in Tomcat. By simply adjusting the autoDeploy and deployOnStartup attributes in your server.xml configuration, you can effectively resolve this problem. Now, you can enjoy the benefits of Java 9 without dealing with servlet duplicates!

Feel free to leave your comments below if you have any questions or additional tips concerning Tomcat configurations!