Unrecognized SSL Message: How Can I Fix This Plaintext Connection Error in My Java Application?

Unrecognized SSL Message: Understanding the Error and Finding a Solution

The error "Unrecognized SSL message, plaintext connection?" usually occurs when a Java application attempts to communicate with an HTTPS server using an insecure connection. This can happen if the port number used is not compatible with HTTPS or if the server's certificate is not trusted.

Cause of the Error

The error message indicates that the server is expecting an SSL-encrypted connection, but the client is sending plaintext data. This can be caused by the following reasons:

• Using the wrong port: HTTPS servers typically use port 443, while HTTP servers use port 80.
• Server certificate not trusted: If the server's certificate is not trusted by the client's JVM, the connection will fail with this error.

Solution

To resolve the error, you can take the following steps:

• Check the port number: Ensure that the Java application is connecting to the HTTPS server using port 443.
• Trust the server certificate: Install the server's certificate in the JVM's truststore. To do this, you can use the keytool command.

Additional Tips

• Ensure that the server's HTTPS configuration is set up correctly and that it is using a valid certificate.
• Disable SSL handshake checks in the Java application if necessary, but be aware of the security implications.
• Consider using a library such as Apache HttpClient or OkHttp to manage SSL connections.

By following these steps, you can resolve the "Unrecognized SSL message, plaintext connection?" error and establish a secure connection to the HTTPS server.

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