Why is my Java JDBC connection failing with a \'TCP/IP connection refused\' error?

JDBC Connection Failure: Understanding the TCP/IP Error

Introduction

Connecting a Java application to an SQL server can sometimes encounter errors. One common issue is the "TCP/IP connection to host failed" error. This error prevents the application from establishing a connection with the database.

Issue

When attempting to connect Java to SQL Server 2012 using JDBC, an error appears:

Error: "The TCP/IP connection to the host 127.0.0.1, port 1433 has failed. Connection refused: connect"

Cause

This error typically occurs due to misconfigurations in the SQL Server network settings. The server may not be listening on the expected port, or firewall restrictions may be blocking communication.

Solution

To resolve this issue, follow these steps:

1. Verify SQL Server Configuration: Open SQL Server Configuration Manager and expand SQL Server 2012 Network Configuration.
2. Enable TCP/IP: Ensure that TCP/IP is enabled under Protocols for InstanceName.
3. Check Listen All: Verify the Listen All option. If set to "yes," the TCP port number is found under TCP Dynamic Ports for IPAll. Otherwise, check under specific IP addresses.
4. Confirm TCP Port: Make sure the TCP port is 1433, which is the default for SQL Server.
5. Address Firewall Restrictions: Ensure that TCP port 1433 is not blocked by Windows Firewall or any other network protections.

Additional Tips

• Ensure the Java driver for SQL Server is correctly registered.
• Check the database connection parameters, including the database name, username, and password.
• Restart SQL Server services if necessary.

By implementing these steps, the TCP/IP connection between Java and SQL Server should be established successfully.

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