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java is agent-read markdown (skill) from yuecao365/offercome: Java 后端怎么面：JVM 与 GC、并发 JUC、Spring、持久层、微服务组件。JD 点名 Java 时读。.

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## 面试官在意什么

Java 后端是国内互联网公司体量最大的后端岗位，日常是在 Spring Boot / Spring Cloud 或 Dubbo 体系里写业务服务、接中间件、处理线上问题。真实面试里 Java 方向有一条非常稳定的主线：JVM 内存与 GC、并发（线程池、锁、JUC 工具）、Spring 原理（IoC、AOP、事务）、持久层（MyBatis/JPA 与连接池）、微服务组件（注册中心、网关、配置中心、RPC）。这些题被问烂了，所以面试官最在意的不是候选人能不能背出 CMS 和 G1 的区别，而是三件事：一是遇到 OOM、CPU 飙高、接口变慢、线程池打满时有没有真实排查过，用什么工具、看什么数据；二是对 Spring 这类"魔法"背后的机制是否真的理解，能否解释自己项目里某个注解为什么不生效；三是并发代码能不能写对，能不能指出一段代码里的竞态。

校招侧重基础：集合源码（HashMap、ConcurrentHashMap）、synchronized 与 ReentrantLock、JVM 内存区域与垃圾回收基本流程、Spring Bean 生命周期、手写线程安全的单例或生产者消费者。社招侧重排查与设计：线上 Full GC 频繁怎么定位、线程池参数怎么定、@Transactional 失效的场景、分布式锁的坑、微服务之间调用超时链路、JDK 17/21 的虚拟线程对现有模型的影响。一线大厂近年明显减少了纯八股，改为"给你一段代码/一个现象，说问题在哪"。

怎么问才像这个方向的面试官：
- 架构与方法论（缓存一致性、消息队列、限流降级）交给 backend 包，本包专注 Java 生态的实现细节与排查手段。
- 八股必须落到现象：任何原理题都要配一个"线上会怎么表现""你怎么验证"的追问，能背不能用的要标记。
- 代码级追问：并发、事务、集合相关主题优先给一段代码或一个现象让候选人找问题，而不是让他复述概念。
- 按 JDK 版本与项目规模出题：还在 JDK 8 的项目不追虚拟线程；小项目不追 ZGC 与容器内存分配，但必须会读 GC 日志与线程栈。
- 2026 年 Java 后端的生产基线是 JDK 21 / 25 与 Spring Boot 3 / 4：虚拟线程接管 IO 密集服务后线程池调优这类老题会反过来问"什么时候不该用虚拟线程"（pinning、CPU 密集、ThreadLocal 膨胀）；紧凑对象头、分代 ZGC、Spring 的 HTTP Service Client 与空安全注解是新的追问点；接大模型的服务会追 Spring AI 一类集成的超时、重试与成本控制。

## 项目 / 实习怎么深挖
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yuecao365/offercome · 23 stars · license MIT · pushed 2026-09-23 · branch main

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