java-patterns

Name: java-patterns
Author: softspark

161stars21forks

How to install java-patterns?

softspark/ai-toolkit/java-patterns

$npx -y skills add softspark/ai-toolkit --skill java-patterns

Installs into the current project.

Summary

Java: Spring Boot, CompletableFuture, records, sealed types, JPA/Hibernate, virtual threads. Triggers: Java, Spring, JPA, Hibernate, Maven, Gradle, virtual thread, sealed class.

Files · 1

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SKILL.md

1	# Java Patterns Skill
2
3	## Project Structure
4
5	### Maven / Gradle Standard Layout
6
7	```
8	my-app/
9	├── pom.xml (or build.gradle.kts + settings.gradle.kts)
10	├── src/
11	│ ├── main/
12	│ │ ├── java/com/example/myapp/
13	│ │ │ ├── MyApplication.java
14	│ │ │ ├── config/
15	│ │ │ ├── controller/
16	│ │ │ ├── service/
17	│ │ │ ├── repository/
18	│ │ │ ├── model/
19	│ │ │ │ ├── entity/
20	│ │ │ │ └── dto/
21	│ │ │ └── exception/
22	│ │ └── resources/
23	│ │ ├── application.yml
24	│ │ └── db/migration/
25	│ └── test/
26	│ ├── java/com/example/myapp/
27	│ └── resources/application-test.yml
28	└── target/ (or build/)
29	```
30
31	### Multi-Module
32
33	```
34	parent/
35	├── pom.xml (packaging=pom)
36	├── common/ (shared utilities)
37	├── domain/ (entities, business rules)
38	├── api/ (REST controllers, DTOs)
39	└── app/ (Spring Boot main, wiring)
40	```
41
42	---
43
44	## Idioms / Code Style
45
46	### Records (Java 16+)
47	```java
48	public record UserDto(Long id, String name, String email) {
49	public UserDto { // compact constructor for validation
50	Objects.requireNonNull(name, "name must not be null");
51	Objects.requireNonNull(email, "email must not be null");
52	}
53	}
54	```
55
56	### Sealed Classes (Java 17+)
57	```java
58	public sealed interface Shape permits Circle, Rectangle, Triangle {
59	double area();
60	}
61	public record Circle(double radius) implements Shape {
62	public double area() { return Math.PI * radius * radius; }
63	}
64	public record Rectangle(double w, double h) implements Shape {
65	public double area() { return w * h; }
66	}
67	public record Triangle(double base, double height) implements Shape {
68	public double area() { return 0.5 * base * height; }
69	}
70	```
71
72	### Switch Expressions (Java 14+)
73	```java
74	String describe(Shape shape) {
75	return switch (shape) {
76	case Circle c -> "Circle r=" + c.radius();
77	case Rectangle r -> "Rect %sx%s".formatted(r.w(), r.h());
78	case Triangle t -> "Triangle base=" + t.base();
79	};
80	}
81	// Guard patterns (Java 21+)
82	String classify(Shape shape) {
83	return switch (shape) {
84	case Circle c when c.radius() > 100 -> "large circle";
85	case Circle c -> "small circle";
86	case Rectangle r -> "rectangle";
87	case Triangle t -> "triangle";
88	};
89	}
90	```
91
92	### var, Streams, Optional
93	```java
94	// var -- use when RHS makes type obvious
95	var users = new ArrayList<User>();
96	var response = client.send(request, HttpResponse.BodyHandlers.ofString());
97	// Avoid: var result = service.process(data); -- type unclear
98
99	// Streams
100	List<String> names = users.stream()
101	.filter(User::isActive)
102	.map(User::name)
103	.sorted()
104	.toList(); // Java 16+, unmodifiable
105
106	Map<Department, List<User>> byDept = users.stream()
107	.collect(Collectors.groupingBy(User::department));
108
109	// Optional -- return type only, never as field or parameter
110	String city = findByEmail(email)
111	.map(User::address)
112	.map(Address::city)
113	.orElse("Unknown");
114	// Never call .get() without guard -- use orElse/orElseThrow
115
116	// Text blocks (Java 15+)
117	String json = """
118	{"name": "%s", "email": "%s"}
119	""".formatted(name, email);
120	```
121
122	---
123
124	## Error Handling
125
126	\| Type \| When \| Examples \|
127	\|------\|------\|---------\|
128	\| Checked \| Recoverable I/O the caller must handle \| IOException, SQLException \|
129	\| Unchecked \| Programming errors, business rule violations \| IllegalArgumentException, custom domain exceptions \|
130
131	### Custom Exception Hierarchy
132	```java
133	public abstract class DomainException extends RuntimeException {
134	private final String errorCode;
135	protected DomainException(String errorCode, String message) {
136	super(message);
137	this.errorCode = errorCode;
138	}
139	public String errorCode() { return errorCode; }
140	}
141
142	public class EntityNotFoundException extends DomainException {
143	public EntityNotFoundException(String entity, Object id) {
144	super("NOT_FOUND", "%s with id %s not found".formatted(entity, id));
145	}
146	}
147	```
148
149	### Try-With-Resources
150	```java
151	try (var conn = dataSource.getConnection();
152	var stmt = conn.prepareStatement(sql);
153	var rs = stmt.executeQuery()) {
154	while (rs.next()) { results.add(mapRow(rs)); }
155	}
156	```
157
158	### Global Handler (Spring)
159	```java
160	@RestControllerAdvice
161	public class GlobalExceptionHandler {
162	@ExceptionHandler(EntityNotFoundException.class)
163	public ResponseEntity<ErrorResponse> handleNotFound(EntityNotFoundException ex) {
164	return ResponseEntity.status(404).body(new ErrorResponse(ex.errorCode(), ex.getMessage()));
165	}
166	@ExceptionHandler(MethodArgumentNotValidException.class)
167	public ResponseEntity<ErrorResponse> handleValidatio

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java-patterns

161stars21forks

View on GitHub

How to install java-patterns?

softspark/ai-toolkit/java-patterns

$npx -y skills add softspark/ai-toolkit --skill java-patterns

Installs into the current project.

Summary

Java: Spring Boot, CompletableFuture, records, sealed types, JPA/Hibernate, virtual threads. Triggers: Java, Spring, JPA, Hibernate, Maven, Gradle, virtual thread, sealed class.

Files · 1

View on GitHub

SKILL.md

1	# Java Patterns Skill
2
3	## Project Structure
4
5	### Maven / Gradle Standard Layout
6
7	```
8	my-app/
9	├── pom.xml (or build.gradle.kts + settings.gradle.kts)
10	├── src/
11	│ ├── main/
12	│ │ ├── java/com/example/myapp/
13	│ │ │ ├── MyApplication.java
14	│ │ │ ├── config/
15	│ │ │ ├── controller/
16	│ │ │ ├── service/
17	│ │ │ ├── repository/
18	│ │ │ ├── model/
19	│ │ │ │ ├── entity/
20	│ │ │ │ └── dto/
21	│ │ │ └── exception/
22	│ │ └── resources/
23	│ │ ├── application.yml
24	│ │ └── db/migration/
25	│ └── test/
26	│ ├── java/com/example/myapp/
27	│ └── resources/application-test.yml
28	└── target/ (or build/)
29	```
30
31	### Multi-Module
32
33	```
34	parent/
35	├── pom.xml (packaging=pom)
36	├── common/ (shared utilities)
37	├── domain/ (entities, business rules)
38	├── api/ (REST controllers, DTOs)
39	└── app/ (Spring Boot main, wiring)
40	```
41
42	---
43
44	## Idioms / Code Style
45
46	### Records (Java 16+)
47	```java
48	public record UserDto(Long id, String name, String email) {
49	public UserDto { // compact constructor for validation
50	Objects.requireNonNull(name, "name must not be null");
51	Objects.requireNonNull(email, "email must not be null");
52	}
53	}
54	```
55
56	### Sealed Classes (Java 17+)
57	```java
58	public sealed interface Shape permits Circle, Rectangle, Triangle {
59	double area();
60	}
61	public record Circle(double radius) implements Shape {
62	public double area() { return Math.PI * radius * radius; }
63	}
64	public record Rectangle(double w, double h) implements Shape {
65	public double area() { return w * h; }
66	}
67	public record Triangle(double base, double height) implements Shape {
68	public double area() { return 0.5 * base * height; }
69	}
70	```
71
72	### Switch Expressions (Java 14+)
73	```java
74	String describe(Shape shape) {
75	return switch (shape) {
76	case Circle c -> "Circle r=" + c.radius();
77	case Rectangle r -> "Rect %sx%s".formatted(r.w(), r.h());
78	case Triangle t -> "Triangle base=" + t.base();
79	};
80	}
81	// Guard patterns (Java 21+)
82	String classify(Shape shape) {
83	return switch (shape) {
84	case Circle c when c.radius() > 100 -> "large circle";
85	case Circle c -> "small circle";
86	case Rectangle r -> "rectangle";
87	case Triangle t -> "triangle";
88	};
89	}
90	```
91
92	### var, Streams, Optional
93	```java
94	// var -- use when RHS makes type obvious
95	var users = new ArrayList<User>();
96	var response = client.send(request, HttpResponse.BodyHandlers.ofString());
97	// Avoid: var result = service.process(data); -- type unclear
98
99	// Streams
100	List<String> names = users.stream()
101	.filter(User::isActive)
102	.map(User::name)
103	.sorted()
104	.toList(); // Java 16+, unmodifiable
105
106	Map<Department, List<User>> byDept = users.stream()
107	.collect(Collectors.groupingBy(User::department));
108
109	// Optional -- return type only, never as field or parameter
110	String city = findByEmail(email)
111	.map(User::address)
112	.map(Address::city)
113	.orElse("Unknown");
114	// Never call .get() without guard -- use orElse/orElseThrow
115
116	// Text blocks (Java 15+)
117	String json = """
118	{"name": "%s", "email": "%s"}
119	""".formatted(name, email);
120	```
121
122	---
123
124	## Error Handling
125
126	\| Type \| When \| Examples \|
127	\|------\|------\|---------\|
128	\| Checked \| Recoverable I/O the caller must handle \| IOException, SQLException \|
129	\| Unchecked \| Programming errors, business rule violations \| IllegalArgumentException, custom domain exceptions \|
130
131	### Custom Exception Hierarchy
132	```java
133	public abstract class DomainException extends RuntimeException {
134	private final String errorCode;
135	protected DomainException(String errorCode, String message) {
136	super(message);
137	this.errorCode = errorCode;
138	}
139	public String errorCode() { return errorCode; }
140	}
141
142	public class EntityNotFoundException extends DomainException {
143	public EntityNotFoundException(String entity, Object id) {
144	super("NOT_FOUND", "%s with id %s not found".formatted(entity, id));
145	}
146	}
147	```
148
149	### Try-With-Resources
150	```java
151	try (var conn = dataSource.getConnection();
152	var stmt = conn.prepareStatement(sql);
153	var rs = stmt.executeQuery()) {
154	while (rs.next()) { results.add(mapRow(rs)); }
155	}
156	```
157
158	### Global Handler (Spring)
159	```java
160	@RestControllerAdvice
161	public class GlobalExceptionHandler {
162	@ExceptionHandler(EntityNotFoundException.class)
163	public ResponseEntity<ErrorResponse> handleNotFound(EntityNotFoundException ex) {
164	return ResponseEntity.status(404).body(new ErrorResponse(ex.errorCode(), ex.getMessage()));
165	}
166	@ExceptionHandler(MethodArgumentNotValidException.class)
167	public ResponseEntity<ErrorResponse> handleValidatio

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