Why Alibaba Prohibits Certain Java Practices: Logging, Collections, Serialization, and More

Alibaba released the Java Development Manual, covering coding conventions, exception logging, unit testing, security, MySQL, project structure, and design guidelines.

1. Logging APIs – Engineers should use a logging facade such as SLF4J with Log4j rather than calling Log4j or Logback APIs directly, to decouple business code from the underlying framework.

2. Collection initialization – Specify initial capacity for collections like HashMap to avoid repeated rehashing; use Guava's

Map<String, String> map = Maps.newHashMapWithExpectedSize(10);

to calculate the optimal size.

3. Modifying collections in foreach loops – The enhanced for‑loop uses an Iterator; modifying the collection directly triggers fail‑fast ConcurrentModificationException. Use an explicit Iterator, a regular for loop, or Stream filtering instead.

4. SimpleDateFormat – Declaring it as static shares the instance across threads, causing thread‑safety issues because it holds mutable state (Calendar). Define it per‑thread or use thread‑safe alternatives.

5. String concatenation in loops – The “+” operator creates a new StringBuilder on each iteration, leading to unnecessary object allocation; prefer a single StringBuilder or String.join.

6. serialVersionUID – Changing this field breaks compatibility between serialized and deserialized classes, causing InvalidClassException; keep it stable unless a deliberate version change is required.

7. subList usage – subList returns a view of the original list; structural changes affect both lists and may throw ConcurrentModificationException. Use a copy when isolation is needed.

8. Inheritance – Inheritance tightly couples subclasses to parent implementations, reducing flexibility; favor composition for better modularity.

9. Variable name isSuccess – Some JSON libraries treat isSuccess as a getter for a boolean property, leading to duplicate fields; rename to success to avoid conflicts.

10. COUNT(*) vs COUNT(col) – COUNT(*) is a SQL‑92 standard optimized by MySQL; counting a column adds a NOT NULL check and is slower.

11. Thread‑pool creation – Using Executors without specifying queue capacity can create unbounded queues, risking OOM; configure bounded queues or use custom ThreadPoolExecutor.

These summaries reflect the author’s personal understanding after studying the manual and illustrate why each rule exists for safer, more efficient backend Java development.