How to Read Java Source Code in IntelliJ IDEA: Complete Navigation Guide

Feb 27, 2026

Purpose

This post demonstrates how to view and navigate Java source code in IntelliJ IDEA. When I try to understand how libraries work internally, I often hit a wall because I can’t see the source code.

Environment

Java 21
IntelliJ IDEA 2024.1
Spring Boot 3.2.x
Maven 3.9.x

The Problem

When I debug Spring Framework code, I get stuck when I try to see what’s happening inside the library. For example:

@RestController
public class UserController {
    @Autowired
    private UserService userService; // Ctrl+B doesn't work - just shows compiled class
}

When I press Ctrl+B on UserService, IntelliJ opens the bytecode instead of the source code. This makes debugging and learning from open source projects difficult.

What I tried first

I tried pressing Ctrl+B everywhere, but it didn’t work for external libraries. I thought maybe IntelliJ had a setting I missed.

I checked my project structure:

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>3.2.1</version>
    </dependency>
</dependencies>

The dependencies are there, but when I Ctrl+B on Spring classes, I get this error in the editor:

Cannot find declaration to go to

How to solve it

I figured out the issue: the source code for external libraries isn’t automatically downloaded. Here’s what I did:

1. Download sources manually

First, I went to File → Project Structure → Libraries. I found the Spring libraries in the list and clicked on one:

Spring Boot :: spring-boot-starter-web (3.2.1)

I clicked the “Download Sources” button. IntelliJ downloaded the source JAR files.

After downloading sources, I pressed Ctrl+B on UserService again, and this time it opened:

// Spring Framework UserService implementation
public class UserService {
    // Now I can see the actual implementation
    public User createUser(User user) {
        // Business logic I wanted to understand
        return userRepository.save(user);
    }
}

2. Enable automatic source downloading

I didn’t want to download sources every time, so I enabled automatic download:

File → Settings → Appearance & Behavior → System Settings
Check “Download source files automatically”

Now when I add new dependencies, IntelliJ automatically downloads the sources.

3. Maven source JARs

For Maven projects, I also added this plugin to ensure source JARs are built:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-source-plugin</artifactId>
            <version>3.3.0</version>
            <executions>
                <execution>
                    <id>attach-sources</id>
                    <goals>
                        <goal>jar</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Ctrl+B / Cmd+B: Go to declaration (my most used shortcut)
Ctrl+Alt+B / Cmd+Option+B: Go to implementations
F4: Go to source (open in editor)
Shift+F4: Open in new tab

When I work on Spring projects, I use these constantly to understand the framework.

Advanced features

Ctrl+Shift+I: Quick documentation lookup
Ctrl+Q: Quick documentation popup
Alt+F7: Find usages
Ctrl+Alt+F7: Find usages in file

These help me understand how classes are used across the codebase.

Structure window

I also use the Structure window (Alt+7) to get an overview of a class:

public class ExampleClass {
    // Fields shown in Structure
    private String field1;

    // Methods listed with signatures
    public void method1() {}
    public String method2() { return "result"; }
}

Why this matters

Understanding source code helps me in several ways:

Learning from open source: I can see how Spring Framework handles dependency injection
Debugging complex issues: When a bug occurs, I can trace through the library code
Improving code quality: I study patterns from production libraries
Understanding framework internals: Knowing how @Autowired works behind the scenes

Common mistakes I made

Not having sources downloaded: This was my main issue
Using only basic navigation: I missed advanced features like finding usages
Forgetting about the Structure window: It gives great context
Not leveraging IntelliJ’s documentation: Sometimes docs are better than source

Summary

In this post, I showed how to view Java source code in IntelliJ IDEA. The key point is enabling source downloading and using Ctrl+B navigation. Now when I work with Spring Framework or other libraries, I can explore the actual source code to understand how things work.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Best open source Java projects for me to read?

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!