I've Been Writing Java for 13 Years, and I Quietly Built a Free Website

Beijing, 3 AM. A few lights are still on in the office building in Greenland. One of them is mine.

My name is Rain, a Java veteran who has been drifting in Beijing for over 13 years. Thirteen years ago, I came here with a laptop and wrote my first "Hello World". I never expected that one keystroke would lead to 13 years.

From business CRUD to architecture design, from payment cores to high-concurrency finance, from big data to AI——I've fought through it all. Today I'm an architect at a well-known internet company, but I'm still on the front lines, drawing diagrams, writing code, and doing reviews.

Recently, I did something rather "foolish"——built a completely free technical website: javadashen.com.

No ads, no paywall, no "add me on WeChat to join a group." Just me, a domain name, and 13 years of hard-earned pitfall notes.

In this article, I want to tell you about this site myself. If you're tormented by interview question banks, stuck in CRUD, or chased by AI anxiety, it's worth five minutes of your time.

1. In an Era of Monetization, Why Did I Do This "Foolish" Thing

The reason is simple, just three "reluctances."

Reluctant to see good technology buried by information gaps. Over the years, I've seen too much best practice and pitfall experience accumulated in big companies that outside people rarely encounter. Many people aren't not working hard; they just have no one to show the way, and they end up taking three to five extra years of detours. I want to lay these out.

Reluctant to watch Java always being talked down. "Java is dead" has been shouted for over a decade, but anyone who has really written it for ten-plus years knows how thick the ecosystem barrier is. It has accompanied me for 13 years, and I want to say something true for it.

Reluctant to see programmers as mere code-writing tools. Beyond the requirements in front of me, I feel there should be some technical faith and resonance with fellow travelers.

In the "About Me" section of the site, I wrote this:

What I most want you to know is——I genuinely love Java. Not just in words; I truly think it's beautiful: the beauty of engineering, the beauty of a vast ecosystem, that sense of solidity that "if you write carefully, it runs steadily."

In an era where everyone talks about monetization, I know this purity is a bit foolish. But foolish is fine; passion can't be hidden.

2. What Did I Put on the Site

I moved in the most valuable things I've accumulated over the years: 151 pages, 146 content items, and more than 130 long practical articles. The whole site is designed around the full chain of "interview—advancement—practice—tools," divided into eight sections:

Section	What problem it solves	Who it's for
High-Frequency Interview Questions	30+ topics, core exam points covered	You preparing to job-hop or sprint for interviews
Scenario Design Questions	47+ real scenarios, fighting for the salary ceiling	You aiming for senior/architect roles
Common Algorithm Questions	18 pattern courses, no big factory without problem-solving	You with weak algorithms, campus or social recruitment
AI Principles & Applications	Java+AI landing, can't survive without AI	Every Java developer who wants to embrace AI
1024 Toolbox	One-stop setup, new machine ready in 5 minutes	All programmers who want to improve efficiency
Slack-off Artifacts	Legal paid slacking, tools all free	You know
Portfolio Projects	One project, one big-factory entrance ticket	You lacking project experience, aiming for a big factory
About Me	A 12-year Beijing Java veteran's true words	All Java fellow travelers

The site is built on VuePress, press Ctrl + K for full-text search, smooth on mobile, properly registered for long-term operation——I'm not here for a quick run; this site will keep being written.

The slogan I wrote for the site is just one sentence: JAVA is the best language in the world. Deeply cultivating Java in the name of passion, and continuing to share with technology as faith. Passion never ends, Java never stops.

When I wrote this, I was a bit embarrassed myself. But how long has it been since we openly talked about "passion" and "faith"?

3. Writing Every Technical Article with Care

Before building this site, I set rules for myself: don't act like a big shot, don't sell anxiety. I just want to explain the source code I've read and the pitfalls I've stepped in, in plain language.

So my way of explaining is special——I don't throw definitions, I focus on "why," and also tell you where the pitfalls are.

I use "cooking" to explain the JVM. For the interview-essential difference between JDK, JRE, and JVM, I made an analogy: JVM is the pot, it just runs bytecode; JRE is pot plus water and seasonings, can run programs but can't cook; JDK is pot, seasonings, knife, and spatula all complete, everything a developer needs. Remember it in one sentence: JDK includes JRE, JRE includes JVM. Hear it once, hard to forget.

I drew Java's decade of evolution as a timeline. From Lambda and Stream in JDK 8, to sealed classes and pattern matching in JDK 17, to virtual threads in JDK 21, one line makes it all clear. And I don't just talk on paper——I actually tested JDK 21 virtual threads: 10,000 concurrent tasks, platform threads take about 50 seconds, virtual threads only about 1 second. A 50x difference. If you say that number in an interview, it's far more persuasive than "I've heard of virtual threads."

I take the "why" into the details. This style runs through the whole site:

For the double-checked locking singleton everyone memorizes, I directly point out: 90% of people write it wrong, missing a single keyword. Without it, instruction reordering can let another thread get a "half-baked" object, and a null pointer exception is waiting ahead. I stepped on this pitfall back then.

For the three-level cache everyone can recite, I insist on asking: why must it be three levels, why not two? The answer lies in AOP——the third level stores not an object but a factory, and only when a real circular dependency occurs does it proactively generate a proxy object. This one sentence is enough to set you apart from people who just memorize.

For new features like Record, I show a comparison: writing a simple data class in JDK 8 takes dozens of lines; after JDK 16, it's one line. Sealed classes combined with pattern matching let the compiler check whether you've handled all cases; miss one and it's a compile error——this is a true "compile-time line of defense."

I always believe that the value of technical content lies not in telling you "what it is," but in telling you "why it's good" and "how to use it correctly."

4. Scenario Design Questions: The Section I Value Most

If interview questions are basic skills, scenario design questions are real combat. This is also the section I personally value most and write the most about, taking up about 40% of the site.

47+ scenarios are all real business problems I've asked in interviews or faced in production——seckill, coupon grabbing, 10-billion-data migration, adding a column to a 10-million-row table, sharding, cache penetration/breakdown/avalanche, MQ backlog, interface idempotency, distributed transactions... Each one is expanded with a fixed template: core challenge, architecture diagram, layered solution, code implementation, technical difficulties, bonus points——no empty talk throughout.

Why do I value this section so much? Look at this table and you'll understand:

Salary level	Capability tested	Typical scenario
20k	Know how to use frameworks	Write a CRUD interface
50k	Design capability	Design a distributed lock solution
100k	Architecture mindset	How to handle Double 11 peak traffic

The gap between 20k and 50k isn't in how many APIs you know, but in whether you can break a business scenario into an implementable technical solution.

Take the classic "How to design a seckill system." My answer is three words: fast, stable, accurate. The overall architecture is five-layer defense, and the essence is also three words: block, shave, differentiate.

Block is intercepting traffic at the door: front-end button graying, CAPTCHA, dynamic URLs first block 90% of traffic; then the gateway does token bucket rate limiting and IP blacklists, so 99.9% of requests never reach the core.

Shave is using message queues to flatten peaks, turning a flood of concurrency into a trickle.

Differentiate is locking stock check, deduction, duplicate order prevention, and async queue entry into one atomic operation——because Redis executes single-threaded, the script runs as a whole and no one can interrupt. Finally, the database keeps an optimistic-lock gate, and overselling is forever eliminated.

I also organized anti-oversell into a four-level degradation plan, so you can match by business traffic:

Level	Solution	Applicable scenario
L1 Fallback	Database atomic update	Low traffic, stability first
L2 General	Optimistic lock version number	Regular business
L3 Conventional	Distributed lock with watchdog auto-renewal	Medium-high concurrency
L4 Seckill	Redis pre-deduction plus stock sharding	Extreme concurrency

Even for the problem most people don't think of, I've thought for you: what if you don't oversell but undersell? The answer is message-queue delayed rollback plus daily reconciliation as a backstop. Say that one line in an interview and you'll directly stand out.

I've interviewed many people, and I'm increasingly convinced: interviewers never ask about knowledge; they ask about how many bullets you've taken.

This section is a lot of information, so if you can't finish reading, you can follow and bookmark it to read slowly.

5. Algorithms and AI: One Is the Entrance Ticket, the Other Is the Future

For the algorithm section, I organized 18 patterns: from two pointers, sliding windows, to dynamic programming. Each type comes with a comparison table of "applicable scenarios, complexity, typical examples," plus real interview simulations and pitfall guides, specifically targeting "forget one after practicing one."

Take the high-frequency LRU cache. 99% of tutorials only teach you to call the ready-made API, but I require you to handwrite it——doubly linked list plus hash table, O(1) for both read and write. Why must it be a doubly linked list? Because a singly linked list needs to find the predecessor when deleting a node, which degenerates to O(n). Why virtual head and tail nodes? To eliminate all boundary checks. These details are exactly what interviewers love to probe. But when it comes to actual work, I also tell you: the JDK built-in implementation is enough; the only key parameter is the access-order switch. Explain principles in interviews, emphasize efficiency at work——only then is this problem truly closed.

But what I want to talk about more is the AI section.

It's 2026. A Java engineer who doesn't understand AI is about equivalent to not understanding distributed systems in 2016. Many sites stop at "what a large model is" when discussing AI, but I go straight to the engineering landing level.

I first clarify the family relationship: AI is the vision, machine learning is the path, deep learning is the heavy weapon, and large language models are the biggest fruit on the deep learning tree.

Then I use one sentence to break down the relationship between Java and AI:

Traditional Java development is "rules + data → results"; AI development is "data + results → rules."

In other words, your engineering ability isn't wasted at all; what you're good at is exactly what AI landing lacks the most. I give 4 transition paths: use Spring AI to turn large-model APIs into services; embed AI capabilities into existing business chains; use LangChain4j to build RAG and intelligent agents; use Flink and Spark to feed large models.

From terminology, prompts, function calling, to vector databases, document chunking, reranking, and then production environment rate limiting, caching, monitoring——the whole package is configured. I even explain experience details like streaming output: what users wait for isn't AI, but the certainty of "characters popping out one by one."

People often ask me: in the AI era, will Java be eliminated? My answer is firm:

Java won't die; what dies is the way Java is written.

Dimension	Java before AI	Java in the AI era
Coding efficiency	Handwritten CRUD	AI-assisted generation of boilerplate
Architecture design	Experience plus documentation	AI-assisted decisions plus experience validation
Debugging	Logs plus guessing	AI analyzing logs plus root cause location
Core competitiveness	Knowing how to write code	Knowing how to design, decide, and use AI

The ecosystem barrier won't disappear. Spring family, JVM tuning, high-concurrency architecture——these abilities that require time to accumulate, AI can't replace for now.

6. Two Easter Eggs: Sharpening Tools, and Legal Slacking

If you think my site is all serious, you're wrong.

In the 1024 Toolbox, multiple JDK versions, MySQL, Redis, Navicat, Maven are all available, so a new machine can be up and running in 5 minutes. Later I'll upgrade it into an online toolbox, with JSON formatting and regex testing all done online.

The Slack-off Artifacts is where I bring my product philosophy to life. It's a separate site, with a slogan written like this:

What your fingertips slide across isn't a screen; it's the progress bar of life. Slacking is tactics; working is a losing battle. Every time you slack off, you're preserving the fire of internet civilization.

Click in with a smile, and you'll find the features are serious: a one-page aggregation of hot lists from a dozen platforms including Baidu, Bilibili, Zhihu, NetEase Cloud, CSDN, Juejin; a "Today in History" timeline; one-click switching among multiple search engines; even new song charts and tech hot lists——slacking off without missing industry trends.

I always believe: pace yourself, that's how a long-distance runner wins.

7. Portfolio Project: 207 Test Cases Are the Best Documentation

The last section to mention is Portfolio Projects——one project, one big-factory entrance ticket.

What I'm most proud of is a complete practical project inside it: 207 test cases, all passing. Design patterns, lock-free queues, benchmark tests, self-built RPC framework, rate-limiting components... all features are covered by tests. I call this "tests as documentation," and I've summarized a test-driven learning method: run tests to see effects, then read source code to understand principles, then change code to verify hypotheses.

Imagine that moment: clone the project, type one command, and all 207 tests go green. That kind of "certainty joy" is something anyone who writes code understands.

I often tell newcomers: technology becomes outdated, but problem-solving ability doesn't. Today you learn Stream, tomorrow virtual threads, the day after native compilation——what doesn't change is the methodology of "principles plus practice plus tests."

8. Whatever Stage You're At, Follow That Path

Too much content and don't know where to start? Let me match you up:

Your current state	Suggested route
Student, fresh grad, blank resume	Portfolio projects as foundation, sprint with interview questions and algorithms
1-3 years, want to jump to a big factory	Interview questions, scenario design, algorithms in order, effective in 2-4 weeks
3-5 years, salary bottleneck	Focus on scenario design questions, that's the key to the ceiling
5+ years, want to move to architecture or AI	AI section plus distributed topics, the path is already paved
Tormented by production incidents	The online troubleshooting in scenario design questions keeps you calm
Just want to slack off	The Slack-off Artifacts, open it today

The whole skill tree looks like this:

9. This Site Is Just Getting Started

The site is still growing fast, and my roadmap is clear:

It won't go viral overnight, and it won't disappear overnight. Just like the Java language itself——not flashy, but reliable; not radical, but always evolving.

In Closing

Over the years, I've seen too many ups and downs.

Wave after wave of "Java is dead" arguments come, yet it still sits firmly at the center of the backend world. I've seen newcomers trapped in interview question banks, able to recite String's immutability but unable to write a thread-safe singleton. I've also seen a batch of older programmers lose sleep in the AI wave, fearing they'll be left behind by the era.

This site is written for these people.

For you debugging at 2 AM, for you fresh out of school sprinting for a big factory, for you over 30 wandering in confusion toward architecture or AI, and for you overwhelmed by demands and occasionally wanting to slack off for five minutes.

No ad pop-ups, no paywall, no selling anxiety. Just me, a domain name, and a 13-year note book laid open for you.

The internet is never short of Java tutorials. I'm willing to be the one who tells you my pitfall experience for free.

There's a line on the site that I wrote for myself, and also send to everyone reading this:

Here there are no big shots, only fellow travelers. The pitfalls I've stepped in, don't step again; the experience I've fumbled out, take it directly.

If this article stirred something in you, please give a like and in-app share, and feel free to follow me——from now on, I'll continue writing down the pitfalls I've stepped in and the source code I've read, one by one.

Finally, I want to ask you a question: at which moment did you suddenly feel "this path in technology is worth going on"? Was it the heartbeat of your first Hello World running, or the moment you fixed a production incident late at night? Let's chat in the comments; I'll read every one, and the one that touches me most will be written into my next article.

Passion never ends, Java never stops.

Keep Coding, Keep Loving——I'm waiting for you at javadashen.com.