java-migration

Name: java-migration
Author: decebals

686stars133forks

How to install java-migration?

decebals/claude-code-java/java-migration

$npx -y skills add decebals/claude-code-java --skill java-migration

Installs into the current project.

Summary

Guide for upgrading Java projects between major versions (8→11→17→21→25). Use when user says "upgrade Java", "migrate to Java 25", "update Java version", or when modernizing legacy projects.

Files · 1

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SKILL.md

1	# Java Migration Skill
2
3	Step-by-step guide for upgrading Java projects between major versions.
4
5	## When to Use
6	- User says "upgrade to Java 25" / "migrate from Java 8" / "update Java version"
7	- Modernizing legacy projects
8	- Spring Boot 2.x → 3.x → 4.x migration
9	- Preparing for LTS version adoption
10
11	## Migration Paths
12
13	```
14	Java 8 (LTS) → Java 11 (LTS) → Java 17 (LTS) → Java 21 (LTS) → Java 25 (LTS)
15	│ │ │ │ │
16	└──────────────┴───────────────┴──────────────┴───────────────┘
17	Always migrate LTS → LTS
18	```
19
20	---
21
22	## Quick Reference: What Breaks
23
24	\| From → To \| Major Breaking Changes \|
25	\|-----------\|------------------------\|
26	\| 8 → 11 \| Removed `javax.xml.bind`, module system, internal APIs \|
27	\| 11 → 17 \| Sealed classes (preview→final), strong encapsulation \|
28	\| 17 → 21 \| Pattern matching changes, `finalize()` deprecated for removal \|
29	\| 21 → 25 \| Security Manager removed, Unsafe methods removed, 32-bit dropped \|
30
31	---
32
33	## Migration Workflow
34
35	### Step 1: Assess Current State
36
37	```bash
38	# Check current Java version
39	java -version
40
41	# Check compiler target in Maven
42	grep -r "maven.compiler" pom.xml
43
44	# Find usage of removed APIs
45	grep -r "sun\." --include="*.java" src/
46	grep -r "javax\.xml\.bind" --include="*.java" src/
47	```
48
49	### Step 2: Update Build Configuration
50
51	Maven:
52	```xml
53	<properties>
54	<java.version>21</java.version>
55	<maven.compiler.source>${java.version}</maven.compiler.source>
56	<maven.compiler.target>${java.version}</maven.compiler.target>
57	</properties>
58
59	<!-- Or with compiler plugin -->
60	<plugin>
61	<groupId>org.apache.maven.plugins</groupId>
62	<artifactId>maven-compiler-plugin</artifactId>
63	<version>3.12.1</version>
64	<configuration>
65	<release>21</release>
66	</configuration>
67	</plugin>
68	```
69
70	Gradle:
71	```groovy
72	java {
73	toolchain {
74	languageVersion = JavaLanguageVersion.of(21)
75	}
76	}
77	```
78
79	### Step 3: Fix Compilation Errors
80
81	Run compile and fix errors iteratively:
82	```bash
83	mvn clean compile 2>&1 \| head -50
84	```
85
86	### Step 4: Run Tests
87
88	```bash
89	mvn test
90	```
91
92	### Step 5: Check Runtime Warnings
93
94	```bash
95	# Run with illegal-access warnings
96	java --illegal-access=warn -jar app.jar
97	```
98
99	---
100
101	## Java 8 → 11 Migration
102
103	### Removed APIs
104
105	\| Removed \| Replacement \|
106	\|---------\|-------------\|
107	\| `javax.xml.bind` (JAXB) \| Add dependency: `jakarta.xml.bind-api` + `jaxb-runtime` \|
108	\| `javax.activation` \| Add dependency: `jakarta.activation-api` \|
109	\| `javax.annotation` \| Add dependency: `jakarta.annotation-api` \|
110	\| `java.corba` \| No replacement (rarely used) \|
111	\| `java.transaction` \| Add dependency: `jakarta.transaction-api` \|
112	\| `sun.misc.Base64*` \| Use `java.util.Base64` \|
113	\| `sun.misc.Unsafe` (partially) \| Use `VarHandle` where possible \|
114
115	### Add Missing Dependencies (Maven)
116
117	```xml
118	<!-- JAXB (if needed) -->
119	<dependency>
120	<groupId>jakarta.xml.bind</groupId>
121	<artifactId>jakarta.xml.bind-api</artifactId>
122	<version>4.0.1</version>
123	</dependency>
124	<dependency>
125	<groupId>org.glassfish.jaxb</groupId>
126	<artifactId>jaxb-runtime</artifactId>
127	<version>4.0.4</version>
128	<scope>runtime</scope>
129	</dependency>
130
131	<!-- Annotation API -->
132	<dependency>
133	<groupId>jakarta.annotation</groupId>
134	<artifactId>jakarta.annotation-api</artifactId>
135	<version>2.1.1</version>
136	</dependency>
137	```
138
139	### Module System Issues
140
141	If using reflection on JDK internals, add JVM flags:
142	```bash
143	--add-opens java.base/java.lang=ALL-UNNAMED
144	--add-opens java.base/java.util=ALL-UNNAMED
145	```
146
147	Maven Surefire:
148	```xml
149	<plugin>
150	<groupId>org.apache.maven.plugins</groupId>
151	<artifactId>maven-surefire-plugin</artifactId>
152	<configuration>
153	<argLine>
154	--add-opens java.base/java.lang=ALL-UNNAMED
155	</argLine>
156	</configuration>
157	</plugin>
158	```
159
160	### New Features to Adopt
161
162	```java
163	// var (local variable type inference)
164	var list = new ArrayList<String>(); // instead of ArrayList<String> list = ...
165
166	// String methods
167	" hello ".isBlank(); // true for whitespace-only
168	" hello ".strip(); // better trim() (Unicode-aware)
169	"line1\nline2".lines(); // Stream<String>
170	"ha".repeat(3); // "hahaha"
171
172	// Collection factory methods (Java 9+)
173	List.of("a", "b", "c"); // immutable list
174	Set.of(1, 2, 3); // immutable set
175	Map.of("k1", "v1"); // immutable map
176
177	// Optional improvements
178	optional.ifPresentOrElse(
179	value -> process(value),
180	() -> handleEmpty()
181	);
182
183	// HTTP Client (replaces HttpURLConnection)
184	HttpClient client = HttpClient.newHttpClient();
185	HttpRequest request = HttpRequest.newBuilder()
186	.uri(URI.create("https://api.example.com"))
187	.build();
188	HttpResponse<String> response = client.send(request,
189	HttpResponse.BodyHandlers.ofString());
190	```
191
192	-

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Type

java-migration

686stars133forks

View on GitHub

How to install java-migration?

decebals/claude-code-java/java-migration

$npx -y skills add decebals/claude-code-java --skill java-migration

Installs into the current project.

Summary

Guide for upgrading Java projects between major versions (8→11→17→21→25). Use when user says "upgrade Java", "migrate to Java 25", "update Java version", or when modernizing legacy projects.

Files · 1

View on GitHub

SKILL.md

1	# Java Migration Skill
2
3	Step-by-step guide for upgrading Java projects between major versions.
4
5	## When to Use
6	- User says "upgrade to Java 25" / "migrate from Java 8" / "update Java version"
7	- Modernizing legacy projects
8	- Spring Boot 2.x → 3.x → 4.x migration
9	- Preparing for LTS version adoption
10
11	## Migration Paths
12
13	```
14	Java 8 (LTS) → Java 11 (LTS) → Java 17 (LTS) → Java 21 (LTS) → Java 25 (LTS)
15	│ │ │ │ │
16	└──────────────┴───────────────┴──────────────┴───────────────┘
17	Always migrate LTS → LTS
18	```
19
20	---
21
22	## Quick Reference: What Breaks
23
24	\| From → To \| Major Breaking Changes \|
25	\|-----------\|------------------------\|
26	\| 8 → 11 \| Removed `javax.xml.bind`, module system, internal APIs \|
27	\| 11 → 17 \| Sealed classes (preview→final), strong encapsulation \|
28	\| 17 → 21 \| Pattern matching changes, `finalize()` deprecated for removal \|
29	\| 21 → 25 \| Security Manager removed, Unsafe methods removed, 32-bit dropped \|
30
31	---
32
33	## Migration Workflow
34
35	### Step 1: Assess Current State
36
37	```bash
38	# Check current Java version
39	java -version
40
41	# Check compiler target in Maven
42	grep -r "maven.compiler" pom.xml
43
44	# Find usage of removed APIs
45	grep -r "sun\." --include="*.java" src/
46	grep -r "javax\.xml\.bind" --include="*.java" src/
47	```
48
49	### Step 2: Update Build Configuration
50
51	Maven:
52	```xml
53	<properties>
54	<java.version>21</java.version>
55	<maven.compiler.source>${java.version}</maven.compiler.source>
56	<maven.compiler.target>${java.version}</maven.compiler.target>
57	</properties>
58
59	<!-- Or with compiler plugin -->
60	<plugin>
61	<groupId>org.apache.maven.plugins</groupId>
62	<artifactId>maven-compiler-plugin</artifactId>
63	<version>3.12.1</version>
64	<configuration>
65	<release>21</release>
66	</configuration>
67	</plugin>
68	```
69
70	Gradle:
71	```groovy
72	java {
73	toolchain {
74	languageVersion = JavaLanguageVersion.of(21)
75	}
76	}
77	```
78
79	### Step 3: Fix Compilation Errors
80
81	Run compile and fix errors iteratively:
82	```bash
83	mvn clean compile 2>&1 \| head -50
84	```
85
86	### Step 4: Run Tests
87
88	```bash
89	mvn test
90	```
91
92	### Step 5: Check Runtime Warnings
93
94	```bash
95	# Run with illegal-access warnings
96	java --illegal-access=warn -jar app.jar
97	```
98
99	---
100
101	## Java 8 → 11 Migration
102
103	### Removed APIs
104
105	\| Removed \| Replacement \|
106	\|---------\|-------------\|
107	\| `javax.xml.bind` (JAXB) \| Add dependency: `jakarta.xml.bind-api` + `jaxb-runtime` \|
108	\| `javax.activation` \| Add dependency: `jakarta.activation-api` \|
109	\| `javax.annotation` \| Add dependency: `jakarta.annotation-api` \|
110	\| `java.corba` \| No replacement (rarely used) \|
111	\| `java.transaction` \| Add dependency: `jakarta.transaction-api` \|
112	\| `sun.misc.Base64*` \| Use `java.util.Base64` \|
113	\| `sun.misc.Unsafe` (partially) \| Use `VarHandle` where possible \|
114
115	### Add Missing Dependencies (Maven)
116
117	```xml
118	<!-- JAXB (if needed) -->
119	<dependency>
120	<groupId>jakarta.xml.bind</groupId>
121	<artifactId>jakarta.xml.bind-api</artifactId>
122	<version>4.0.1</version>
123	</dependency>
124	<dependency>
125	<groupId>org.glassfish.jaxb</groupId>
126	<artifactId>jaxb-runtime</artifactId>
127	<version>4.0.4</version>
128	<scope>runtime</scope>
129	</dependency>
130
131	<!-- Annotation API -->
132	<dependency>
133	<groupId>jakarta.annotation</groupId>
134	<artifactId>jakarta.annotation-api</artifactId>
135	<version>2.1.1</version>
136	</dependency>
137	```
138
139	### Module System Issues
140
141	If using reflection on JDK internals, add JVM flags:
142	```bash
143	--add-opens java.base/java.lang=ALL-UNNAMED
144	--add-opens java.base/java.util=ALL-UNNAMED
145	```
146
147	Maven Surefire:
148	```xml
149	<plugin>
150	<groupId>org.apache.maven.plugins</groupId>
151	<artifactId>maven-surefire-plugin</artifactId>
152	<configuration>
153	<argLine>
154	--add-opens java.base/java.lang=ALL-UNNAMED
155	</argLine>
156	</configuration>
157	</plugin>
158	```
159
160	### New Features to Adopt
161
162	```java
163	// var (local variable type inference)
164	var list = new ArrayList<String>(); // instead of ArrayList<String> list = ...
165
166	// String methods
167	" hello ".isBlank(); // true for whitespace-only
168	" hello ".strip(); // better trim() (Unicode-aware)
169	"line1\nline2".lines(); // Stream<String>
170	"ha".repeat(3); // "hahaha"
171
172	// Collection factory methods (Java 9+)
173	List.of("a", "b", "c"); // immutable list
174	Set.of(1, 2, 3); // immutable set
175	Map.of("k1", "v1"); // immutable map
176
177	// Optional improvements
178	optional.ifPresentOrElse(
179	value -> process(value),
180	() -> handleEmpty()
181	);
182
183	// HTTP Client (replaces HttpURLConnection)
184	HttpClient client = HttpClient.newHttpClient();
185	HttpRequest request = HttpRequest.newBuilder()
186	.uri(URI.create("https://api.example.com"))
187	.build();
188	HttpResponse<String> response = client.send(request,
189	HttpResponse.BodyHandlers.ofString());
190	```
191
192	-

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Type