java-expert

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Keyword: java | Platforms: gemini,claude,codex

High-Performance Modern Java Expert Skill - Specialized in Java 21+ and cloud-native architecture.

关键词：java | 支持平台：gemini、claude、codex

高性能现代Java专家技能 - 专注于Java 21+和云原生架构。

Java 21+ First: Mandate
```
var
```
(LVTI) where readable, Records for DTOs, and Pattern Matching for
```
instanceof
```
and
```
switch
```
.
Concurrency: Prefer Virtual Threads (
```
@RunOnVirtualThread
```
in Quarkus or
```
Executors.newVirtualThreadPerTaskExecutor()
```
) over traditional Thread Pools for I/O-bound tasks.
Immutability: Use
```
record
```
,
```
final
```
fields, and
```
unmodifiable
```
collections (
```
List.of
```
,
```
Map.of
```
).
Functional Style: Leverage Streams,
```
Optional
```
, and Functional Interfaces to reduce boilerplate and side effects.
Visibility: Default to
```
package-private
```
or
```
private
```
. Only
```
public
```
what must be exposed (API/SPI).

优先使用Java 21+： 在可读性允许的情况下强制使用
```
var
```
（LVTI），用Records实现DTO，以及在
```
instanceof
```
和
```
switch
```
中使用模式匹配。
并发处理： 对于I/O密集型任务，优先使用Virtual Threads（Quarkus中的
```
@RunOnVirtualThread
```
或
```
Executors.newVirtualThreadPerTaskExecutor()
```
）而非传统线程池。
不可变性： 使用
```
record
```
、
```
final
```
字段和不可修改集合（
```
List.of
```
、
```
Map.of
```
）。
函数式风格： 利用Streams、
```
Optional
```
和函数式接口减少样板代码和副作用。
可见性： 默认使用包私有或私有访问修饰符。仅对外暴露必须公开的内容（API/SPI）。

Domain: Pure Java, zero external dependencies (no Quarkus/Spring in domain classes).
Ports (Interfaces): Define input (Use Cases) and output (Repositories, Gateways) interfaces.
Adapters: Infrastructure implementations (Quarkus/Hibernate/REST) reside outside the domain.

Garbage Collection: Favor G1GC for typical workloads or ZGC for ultra-low latency (<1ms).
Memory Management: Minimize object allocation in hot loops. Use
```
StringBuilder
```
instead of
```
+
```
in loops.
Profiling: Use JFR (Java Flight Recorder) for production-safe profiling and bottleneck analysis.

JUnit 5 & AssertJ: The industry standard for fluent, readable assertions.
Mockito: Deep stubbing and spying for complex dependencies.
ArchUnit: Enforce architectural rules (e.g., "Domain must not depend on Infrastructure").
Testcontainers: Real-world integration testing for databases (PostgreSQL, MySQL) and brokers (Kafka, Redis).

Jandex: Understand Jandex indexing for Quarkus's fast annotation scanning.
Bytecode Manipulation: Familiarity with ASM or ByteBuddy for runtime/build-time enhancement.
ClassLoader Isolation: Debugging issues related to "parent-first" vs "child-first" delegation.

The java-expert ☕ skill provides the foundational language expertise (JDK 21+, Virtual Threads) required by:

java-expert ☕技能提供了以下技能所需的基础语言专业知识（JDK 21+、Virtual Threads）：