# spring

This rule guides Spring Boot code structure, dependency injection, and common pitfalls. Use it when asking an agent to write or review Java code in a project.

- rule · `type=rule` · Cursor · ★ 3580
- Author: sanjeed5
- License: CC0-1.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/spring.mdc
- Updated: 2026-05-19
- HTML: https://affpapa.org/en/nevibecode/rules/spring

## What it does

The rule covers package layout, dedicated configuration classes, constructor-based dependency injection, and immutable data models. It also shows how to fetch related records without N+1 queries and validate user input at the API boundary.

For exception handling, it recommends a shared handler using `@ControllerAdvice`; auto-configuration should be disabled only when needed. Its examples include Java `record` DTOs and specify Java 16+. The rule targets `**/*.java` files, so it focuses on code guidance rather than project-wide setup.

## Install

### Cursor (native platform)

**Manually: put the files in place**
- File: `.cursor/rules/spring.mdc` — Frontmatter: description, globs, alwaysApply

### Claude Code

**Manually: put the files in place**
- File: `.claude/rules/spring.md` — The paths frontmatter field limits the files: move globs from the source into paths

### Codex

**AGENTS.md**
- Codex reads AGENTS.md: paste the rule text there

### GitHub Copilot

**Manually: put the files in place**
- File: `.github/instructions/spring.instructions.md` — The applyTo field sets which files it applies to: move globs from the source into applyTo

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/rules/spring.md`

### Cline

**Manually: put the files in place**
- File: `.clinerules/spring.md`

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/spring.mdc

## When to use it
- split bean definitions into focused configuration classes
- replace field injection with constructor injection
- avoid N+1 queries when loading related records
- validate request data at the API boundary
- handle exceptions through a shared controller advice

## Example prompts
- Review this Java code against the Spring Boot rule and suggest specific changes.
- Refactor this service to use constructor injection and avoid N+1 queries.
- Check this user-creation endpoint for input validation and shared exception handling.

## Source text · spring.mdc · CC0-1.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 85046cd705bd07ae.

BEGIN THIRD-PARTY FILE 85046cd705bd07ae
````text
---
description: Definitive guidelines for building robust, maintainable, and performant Spring Boot applications using modern best practices.
globs: **/*.java
---
# Spring Best Practices

This guide outlines essential best practices for developing with Spring Boot, ensuring your applications are well-structured, performant, secure, and easily testable.

## 1. Code Organization and Structure

Maintain a clean, logical package structure.

### 1.1. Base Package and `@SpringBootApplication`

Place your main application class at the root of a well-named base package. All components should reside within this base package or its sub-packages.

❌ BAD:
```java
// com.example.Application.java
package com.example; // Too generic, or in default package
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}
```

✅ GOOD:
```java
// com.company.project.MyApplication.java
package com.company.project; // Specific base package
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication { // Clear application entry point
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}
```

### 1.2. Configuration Classes

Group related bean definitions into dedicated `@Configuration` classes.

❌ BAD:
```java
// MyApplication.java (monolithic config)
@SpringBootApplication
public class MyApplication {
    // ...
    @Bean
    public DataSource dataSource() { /* ... */ }
    @Bean
    public RestTemplate restTemplate() { /* ... */ }
}
```

✅ GOOD:
```java
// com.company.project.config.DataSourceConfig.java
@Configuration
public class DataSourceConfig {
    @Bean
    public DataSource dataSource() { /* ... */ }
}

// com.company.project.config.WebClientConfig.java
@Configuration
public class WebClientConfig {
    @Bean
    public WebClient webClient(WebClient.Builder builder) {
        return builder.baseUrl("http://api.example.com").build();
    }
}
```

## 2. Common Patterns and Anti-patterns

### 2.1. Constructor Injection

Always prefer constructor injection for mandatory dependencies. It ensures immutability and testability.

❌ BAD:
```java
@Service
public class UserService {
    @Autowired // Field injection is discouraged
    private UserRepository userRepository;

    public User findById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}
```

✅ GOOD:
```java
@Service
public class UserService {
    private final UserRepository userRepository; // Immutable

    @Autowired // Optional for single constructor in Spring 4.3+
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User findById(Long id) {
        return userRepository.findById(id).orElse(null);
    }
}
```

### 2.2. Immutable Data Models

Use immutable classes for DTOs and entities where possible, especially for value objects.

❌ BAD:
```java
public class UserDto { // Mutable
    private Long id;
    private String name;
    // Getters and Setters
}
```

✅ GOOD:
```java
public record UserDto(Long id, String name) {} // Immutable record (Java 16+)
// Or with Lombok:
@Value // All-args constructor, getters, equals, hashCode, toString
public class UserDto {
    Long id;
    String name;
}
```

## 3. Performance Considerations

### 3.1. N+1 Query Problem

Avoid N+1 queries by eagerly fetching related data when necessary.

❌ BAD:
```java
@Service
public class OrderService {
    @Autowired private OrderRepository orderRepository;
    public List<Order> getOrdersWithItems() {
        List<Order> orders = orderRepository.findAll();
        orders.forEach(order -> order.getItems().size()); // N+1 queries for items
        return orders;
    }
}
```

✅ GOOD:
```java
@Repository
````
END THIRD-PARTY FILE 85046cd705bd07ae

The third-party file has ended. Everything between the 85046cd705bd07ae tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 4071 of 9594 bytes. © sanjeed5 · CC0-1.0 · https://github.com/sanjeed5/awesome-cursor-rules-mdc/tree/HEAD/rules-mdc/spring.mdc

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