A Detailed Java Troubleshooting Guide

Network troubleshooting in Java

Next, let’s discuss some common networking related problems.

Issue – Connection timeouts

Description: Your Java application fails to establish connections to external servers or services within specified time limits.

Detection: You may see exceptions, errors, or stack traces related to timeouts in the logs.

Troubleshooting:

• Ensure that firewalls are not blocking the connection. Check the firewall rules of your system, network, and cloud environment.
• If the network is slow or the server is under load, try increasing the connection and read timeout settings.
• Ensure that the server's IP and port are correct and accessible. If you're using a proxy, verify that the proxy settings are correct.
• Use tools like ping, traceroute, or telnet to check if the server is reachable from the application’s environment.
• If nothing else works, try capturing network packets using the tcpdump utility and analyzing them via a tool like Wireshark.

Issue – Socket exceptions

Description: You are experiencing closed sockets, connection resets, or problems with the underlying network infrastructure.

Detection: The logs show exceptions such as java.net.SocketException or java.net.SocketTimeoutException.

Troubleshooting:

• Verify that sockets are properly opened and closed in your code.
• Connection resets are often caused by abrupt disconnections on the server or client side. You can handle this by catching the SocketException and implementing retry logic. For example:

try {
Socket socket = new Socket("example.com", 80);
// communication code
} catch (SocketException e) {
// Retry or log the error
    System.out.println("Socket error: " + e.getMessage());
} 

• Verify the stability of your network. Unreliable network connections can lead to frequent socket errors. If you are on wireless, try using a wired connection.
• Enable TCP keep-alive to maintain long-lived connections.
• If nothing else works, test your app on an entirely different network to rule out network instability.

Issue – Slow network performance

Description: Your application is experiencing sluggish network performance.

Detection: You notice long delays in receiving data, increased latency in communication with servers, or timeouts during data transfers.

Troubleshooting:

• If your application is sending or receiving large amounts of data, ensure that you’re using efficient mechanisms like buffering to prevent bottlenecks. For example, you can use BufferedInputStream and BufferedOutputStream to improve I/O performance.
• If network operations block the main thread, consider using non-blocking or asynchronous I/O to improve performance. Java’s NIO package allows you to use non-blocking sockets.
• Use tools like iperf to measure bandwidth and latency. If your application’s environment has limited bandwidth or high latency, consider adjusting your timeout settings or reducing the amount of data sent per request.
• You can also enable compression to reduce the amount of data being sent over the network. Here’s an example:
  
  

  connection.setRequestProperty("Accept-Encoding", "gzip");

Issue – DNS resolution issues

Description: Your Java application is unable to resolve domain names of external services.

Detection: You may see errors or exceptions like java.net.UnknownHostException in the application logs.

Troubleshooting:

• Ensure that your system's DNS settings are correct. You can verify the DNS server by checking your system's network configuration or /etc/resolv.conf (on Linux).
• Temporarily replace domain names with IP addresses to check if DNS resolution is the issue.
• If needed, you can configure custom DNS servers in your Java application like this:
  

  System.setProperty("sun.net.spi.nameservice.nameservers", "8.8.8.8"); 
  System.setProperty("sun.net.spi.nameservice.provider.1", "dns,sun"); 

• Clear any stale DNS cache that may be causing incorrect resolution by running commands like ipconfig /flushdns (Windows) or sudo dscacheutil -flushcache (macOS).

Memory troubleshooting in Java

Java's garbage collector automatically manages memory allocation and deallocation. However, if objects are no longer needed, but references to them still exist, such objects can evade deallocation, leading to memory leaks. This section dissects some memory-related problems, including memory leaks.

Issue – Memory leaks

Description: Memory leaks are causing your application to consume more memory than it should.

Detection: You see a gradual increase in your application’s memory footprint over time.

Troubleshooting:

• Use memory profiling tools to analyze heap dumps and identify objects that are not being released. Check for references that prevent objects from being garbage collected (e.g., static references, collections that are not cleared).
• Ensure that resources like database connections, file handles, and network sockets are properly closed. Consider using Java’s try-with-resources to automatically close resources.
• If your code registers listeners, make sure they are unregistered when no longer needed. Otherwise, they can hold onto objects indefinitely, leading to memory leaks.

Issue – Excessive garbage collection activity

Description: Too much garbage collection is degrading overall application performance.

Detection: You can start tracking garbage collection by enabling the GC logs using the -Xlog:gc option. If the logs show frequent GC pauses or messages like GC overhead limit exceeded, this is typically a sign of excessive GC.

Troubleshooting:

• Review your code for excessive object creation, especially in loops. Try reusing objects or pooling them instead of repeatedly creating and destroying new instances.
• If feasible, allocate more memory to the JVM so that garbage collection occurs less frequently.
• Experiment with different garbage collectors. For example, switching to G1GC can reduce GC pauses and improve performance in applications with large heaps.

Issue – Memory fragmentation

Description: Fragmented memory is leading to unexpected behavior in your application.

Detection: Some symptoms of memory fragmentation include: frequent full GC cycles and increasing heap usage despite the total memory usage being relatively low. Memory fragmentation is more common in long-running applications that frequently allocate and deallocate memory.

Troubleshooting:

• Use garbage collectors like G1GC, which can help reduce memory fragmentation by compacting the heap during garbage collection.
• If you’re using a garbage collector that supports it, enable heap compaction to defragment memory and consolidate free memory blocks.
• While not a direct solution, you can consider increasing the heap size to reduce the impact of fragmentation by allowing larger contiguous memory blocks to be allocated.

Thread troubleshooting in Java

Multithreading in Java offers several benefits, but can also introduce complex issues. We will discuss some of them below:

Issue – Thread contention

Description: Multiple threads are attempting to access shared resources (e.g., objects, variables) at the same time, leading to bottlenecks.

Detection:

• You experience slow response times, reduced throughput, or high CPU usage without significant work being done.
• Profiling tools like JVisualVM, YourKit, or JProfiler can also help detect contention by highlighting waiting or blocked threads.

Troubleshooting:

• Instead of locking large blocks of code, only lock the critical sections that need to be synchronized. This reduces the waiting time for threads.
• For some use cases, lock-free data structures (e.g., java.util.concurrent package) can reduce contention. For example, you can consider using ConcurrentHashMap instead of HashMap in multithreaded environments.
• Reduce the number of shared objects or variables between threads. If possible, assign dedicated resources to each thread to avoid contention.

Issue – Deadlocks

Description: Two or more threads are blocked forever, causing your application to go into a deadlock.

Detection: Your application seems to hang indefinitely.

Troubleshooting:

• Deadlocks often occur when multiple locks are held simultaneously. Avoid acquiring multiple locks inside a synchronized block, and try to ensure that locks are always acquired in the same order across all threads.
• Use Java’s ReentrantLock class with a timeout instead of synchronized blocks to prevent indefinite blocking.
• Enable JVM deadlock detection using tools like JConsole or JVisualVM to monitor thread activity. Regularly check for potential deadlocks in complex systems.

Issue – Race conditions

Description: Two or more threads are trying to access the same data simultaneously, leading to non-deterministic behavior.

Detection: You are experiencing inconsistent outcomes, especially in calculations, updates, or transactions.

Troubleshooting:

• Synchronize access to shared data to ensure that only one thread can modify the data at a time.
• For simpler shared data, use atomic classes like AtomicInteger or AtomicReference, which provide thread-safe operations without the need for explicit locking.
• If possible, use immutable objects to avoid race conditions. Immutable objects cannot be modified once created, eliminating the need for synchronization.

Issue – Thread starvation

Description: Lower priority threads are perpetually denied CPU time because higher-priority threads are consuming all available resources.

Detection: Thread starvation can result in some tasks not executing or completing within expected timeframes.

Troubleshooting:

• Avoid setting very high or very low thread priorities unless absolutely necessary. The default priority (Thread.NORM_PRIORITY) works well for most applications.
• Use thread pools (e.g., ExecutorService) to manage thread execution. A properly configured thread pool can prevent starvation by distributing tasks evenly across available threads.
• When using locks, ensure they are fair (i.e., they grant access in the order requested). Java’s ReentrantLock class allows you to create a fair lock.

Best practices for writing reliable Java code

Finally, here are some best practices that can help you avoid many of the aforementioned issues, and write more reliable Java code in general:

Adhere to object-oriented programming principles

Java is built around object-oriented programming (OOP). When you adhere to OOP principles like encapsulation, inheritance, and polymorphism, it naturally enables you to create modular, flexible, and reusable code. Always structure your code into logical classes and methods, making it easier to maintain and extend.

Use dependency injection

Dependency injection frameworks like Spring or Java’s CDI (Contexts and Dependency Injection) promote loose coupling between objects, which leads to more maintainable and testable code. This approach also simplifies testing, as dependencies can be easily mocked.

Leverage Java’s built-in concurrency tools

For multi-threaded applications, Java provides a rich set of concurrency tools in the java.util.concurrent package, such as ExecutorService, CountDownLatch, and Semaphore. Use these tools to reduce threading complexity and avoid common pitfalls like deadlocks and race conditions.

Profile and optimize performance early

Incorporate profiling tools like JVisualVM, YourKit, and JProfiler into your development workflow to identify bottlenecks such as memory leaks, high CPU usage, or inefficient I/O. Profiling during development can help catch performance issues before they impact production.

Set up monitoring

Use dedicated monitoring tools, such as the Java Monitoring Tool by Site24x7, to track the health and performance of your application in real time. The Site24x7 tool lets you keep tabs on several key metrics categories, including JVM, database, and background transactions.

Conclusion

Java is a battle-tested programming language that powers a wide range of use cases across industries. Like every other software product, Java applications can occasionally run into issues related to memory, networking, threading, and configurations.Use the troubleshooting advice shared in this guide to enable you to effectively troubleshoot these issues the next time you encounter them.

To monitor your Java app’s performance in real time, don’t forget to incorporate the Site24x7 Java Monitoring Tool into your workflow.