Logo
Tutorials Articles Code Playground Tools
Sign In Get Started
Module: Testing & Debugging

Debugging Tips

Debugging is an essential skill for any developer, and Spring Boot applications are no exception. Here's a breakdown of helpful debugging tips, covering common scenarios and techniques.

1. Understanding Breakpoints

  • Setting Breakpoints: The foundation of debugging. Click in the gutter (the space to the left of the line numbers) in your IDE (IntelliJ IDEA, Eclipse, VS Code) to set a breakpoint. Execution will pause at that line.
  • Conditional Breakpoints: Pause only when a specific condition is met. Right-click on a breakpoint and add a condition (e.g., user.getId() == 123). This is incredibly useful when dealing with loops or large datasets.
  • Field Watchpoints: Monitor the value of a specific variable. Useful for tracking when a variable's value unexpectedly changes. (IDE specific - check your IDE documentation).
  • Method Breakpoints: Break when a specific method is called. Useful for understanding method execution flow without stepping through every line.

2. Using Your IDE's Debugger

  • Step Over (F8): Executes the current line and moves to the next line in the same method. Skips over method calls.
  • Step Into (F7): Executes the current line and, if it's a method call, steps inside that method.
  • Step Out (Shift+F8): Finishes executing the current method and returns to the calling method.
  • Resume (F9): Continues execution until the next breakpoint or the end of the program.
  • Evaluate Expression: Most IDEs allow you to evaluate expressions during debugging. This lets you inspect variable values, call methods, and test conditions in real-time. (Often accessed via Alt+F8 or similar).
  • Watches: Add variables to a "Watches" window to continuously monitor their values as you step through the code.

3. Logging Effectively

While debuggers are powerful, strategic logging can often pinpoint issues faster.

  • Log Levels: Use appropriate log levels:
    • TRACE: Very detailed information, usually only enabled during development.
    • DEBUG: Detailed information useful for debugging.
    • INFO: General information about application operation.
    • WARN: Potential problems or issues that don't necessarily cause failure.
    • ERROR: Errors that prevent the application from functioning correctly.
  • SLF4J & Logback/Log4j2: Spring Boot typically uses SLF4J for logging facades and Logback or Log4j2 as the underlying implementation. Configure these in application.properties or application.yml.
  • Structured Logging: Consider using structured logging (e.g., JSON format) for easier analysis and querying of logs. Libraries like logback-json-classic can help.
  • Correlation IDs: In microservices environments, use correlation IDs to track requests across multiple services. Log the correlation ID with each log message.
logging.level.root=INFO
logging.level.com.example.myapp=DEBUG

4. Spring Boot Specific Debugging

  • @SpringBootApplication & Context Loading: If your application isn't starting, check the logs for errors during context loading. Breakpoints in your @Configuration classes can help identify issues.
  • Auto-Configuration: Spring Boot's auto-configuration can sometimes cause unexpected behavior. Use debug=true in your application.properties to see which auto-configurations are being applied.
  • Data JPA/Hibernate:
    • SQL Logging: Enable SQL logging to see the generated SQL queries. Set logging.level.org.hibernate.SQL=DEBUG or spring.jpa.properties.hibernate.type_descriptor.sql_comments=true.
    • Hibernate Statistics: Enable Hibernate statistics to gather performance metrics.
  • Web Layer:
    • Request Logging: Log incoming requests and responses to understand the data flow. Consider using an interceptor or filter.
    • Controller Advice: Use @ControllerAdvice to handle exceptions globally and log error details.
  • Actuator Endpoints: Spring Boot Actuator provides endpoints for monitoring and managing your application. Use endpoints like /health, /metrics, and /trace to gather information.

5. Common Debugging Scenarios

  • NullPointerExceptions: The bane of every developer. Use breakpoints and evaluate expressions to find where the null value is originating.
  • Configuration Issues: Verify that your properties are being loaded correctly and that your beans are being configured as expected.
  • Database Connection Problems: Check your database connection settings and ensure that the database server is running.
  • Dependency Conflicts: Use your IDE's dependency management tools to identify and resolve dependency conflicts.
  • Unexpected Behavior: Start with a simple test case that reproduces the issue. Then, use breakpoints and logging to step through the code and understand what's happening.

6. Remote Debugging

  • Connect to a Running Application: Useful for debugging applications running in production or on a remote server. Configure your IDE to connect to the remote JVM using a specific port. (Requires JVM arguments like -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005).
  • Security Considerations: Be careful when enabling remote debugging in production, as it can expose your application to security risks. Use strong authentication and restrict access to the debugging port.

7. Tools & Resources

  • Your IDE's Debugger: Master the features of your IDE's debugger.
  • Spring Boot Actuator: For monitoring and managing your application.
  • JProfiler/YourKit: Commercial profiling tools for performance analysis.
  • VisualVM: A free profiling tool.
  • Spring Initializr: Helps create a basic Spring Boot project for testing debugging techniques.

Remember to practice and experiment with these techniques to become a more effective debugger. The more you debug, the better you'll become at identifying and resolving issues quickly.