google/guice

★ 12,744JavaAudience · developerComplexity · 3/5Setup · moderate

Mindmap

mindmap
  root((repo))
    What it does
      Wires dependencies
      Replaces manual new
      Type-safe injection
    Core concepts
      @Inject annotation
      Module configuration
      Binding declarations
    Benefits
      Easier unit testing
      Swap implementations
      Compiler catches errors
    Extensions
      Database persistence
      Spring integration
      Testing utilities
    Setup
      Maven dependency
      javax vs Jakarta

mindmap root((repo)) What it does Wires dependencies Replaces manual new Type-safe injection Core concepts @Inject annotation Module configuration Binding declarations Benefits Easier unit testing Swap implementations Compiler catches errors Extensions Database persistence Spring integration Testing utilities Setup Maven dependency javax vs Jakarta

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Things people build with this

USE CASE 1

Add @Inject to a Java class so Guice automatically provides all its dependencies without calling 'new' manually.

USE CASE 2

Swap a real database or network service for a fake one in unit tests without changing the class being tested.

USE CASE 3

Use a Guice extension to integrate dependency injection with Spring or add database persistence to a Java project.

Tech stack

JavaMaven

Getting it running

Difficulty · moderate Time to first run · 30min

Add a single Maven dependency to get started, extensions for persistence or Spring require additional dependencies.

In plain English

Guice is a Java library from Google that handles a common and tedious problem in software development: managing how different parts of a program get access to the other parts they depend on. In Java, every object that needs another object must either create it with the "new" keyword or ask a factory class to hand one over. Guice replaces most of that boilerplate with a simple annotation called @Inject, which tells the framework to supply the right object automatically. The practical benefit is that code becomes easier to test, because in tests you can swap out a real database or network connection for a fake one without rewriting the class being tested. It also makes code easier to reuse across different contexts, since the class itself does not know or care where its dependencies come from. Guice stays close to Java's type system, which means the compiler can catch mistakes rather than letting them show up at runtime. The library was designed to give helpful error messages when something goes wrong, which makes debugging faster. Google has used it in production systems since 2006. The project ships as a Maven dependency for easy inclusion in Java projects, and it offers several optional extensions covering areas like database persistence, Spring integration, and testing utilities. Both a stable release and a newer version that supports the updated Jakarta namespace are available, with the two being otherwise equivalent in features.

Copy-paste prompts

Prompt 1

Set up Google Guice in a Maven Java project and create a simple Module that binds a service interface to a concrete implementation.

Prompt 2

Show me how to use Guice to inject a mock database connection in a JUnit test so I can test a service class in isolation.

Prompt 3

I have a Java class with three constructor dependencies, convert it to use Guice @Inject and write the corresponding Module binding.

Prompt 4

My Java project uses javax.inject but I need to migrate to the Jakarta namespace, show me how to update my Guice version and imports.

Prompt 5

Write a Guice Module that provides a configured HTTP client as a singleton so all classes that need it share the same instance.

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