Java → Go Cheatsheet

在 Go Chat 專案中實際用到的所有對照

語言基礎

Java	Go
class Todo	type Todo struct
public / private	大寫開頭 / 小寫開頭
new Constructor()	NewXxx() function
this	method receiver (s *Store)
implements Interface	隱式（有對應 method 就算）
ArrayList<T>	[]T（slice）
HashMap<K,V>	map[K]V
null	nil
try-catch	if err != nil
throw new Exception()	return fmt.Errorf()
finally	defer
Thread	goroutine（go func()）
BlockingQueue	channel（chan T）
synchronized	sync.Mutex
CompletableFuture	goroutine + channel
Optional<T>	多值回傳 (T, error)

HTTP 框架：Spring → Gin

Spring	Gin
@RestController	r.GET("/path", handler)
@GetMapping / @PostMapping	r.GET / r.POST
@RequestBody	c.ShouldBindJSON(&obj)
@PathVariable	c.Param("id")
@RequestParam	c.Query("name")
ResponseEntity.ok(data)	c.JSON(200, data)
@RequestMapping("/api")	r.Group("/api")
HttpServletRequest	*gin.Context
@Valid / @NotNull	binding:"required"

Middleware：Filter → gin.HandlerFunc

Spring	Gin
implements Filter	func() gin.HandlerFunc
chain.doFilter(req, res)	c.Next()
不呼叫 chain.doFilter	c.Abort()
request.setAttribute()	c.Set(key, value)
request.getAttribute()	c.GetString(key)
antMatchers("/ws").authenticated()	group.Use(JWTAuth())

ORM：JPA / Hibernate → GORM

JPA	GORM
@Entity	type User struct + struct tag
@Id @GeneratedValue	gorm:"primaryKey"
@Column(unique = true)	gorm:"uniqueIndex"
@JsonIgnore	json:"-"
repository.save(entity)	DB.Create(&entity)
repository.findById(id)	DB.First(&entity, id)
repository.findByUsername(x)	DB.Where("username = ?", x).First(&entity)
ddl-auto=update	DB.AutoMigrate(&User{})
EntityManagerFactory	gorm.Open(postgres.Open(dsn))

認證：Spring Security → 手動

Spring	Go
BCryptPasswordEncoder	bcrypt.GenerateFromPassword
Jwts.builder().setClaims()	jwt.NewWithClaims(HS256, claims)
Jwts.parser().parseClaimsJws()	jwt.Parse(token, keyFunc)
@AuthenticationPrincipal	c.GetFloat64("user_id")
SecurityContextHolder	gin.Context（request scope）
ThreadLocal	context 顯式傳遞

WebSocket

Java (Spring WebSocket)	Go (gorilla/websocket)
@ServerEndpoint	upgrader.Upgrade(w, r, nil)
@OnMessage	conn.ReadMessage() in readPump goroutine
@OnClose	defer in readPump
session.getBasicRemote().sendText()	conn.WriteMessage() in writePump goroutine
容器管理 session	自己寫 Hub 管理 Client map

專案結構

Spring Boot	Go
src/main/java/	cmd/server/（進入點）+ internal/（業務碼）
com.example.controller	internal/handler/
com.example.service	internal/service/
com.example.repository	internal/repository/
com.example.model	internal/model/
application.yml	.env + config/config.go
pom.xml / build.gradle	go.mod
@Autowired	手動傳入（constructor injection）

開發工具

Java	Go
mvn spring-boot:run	go run ./cmd/server/
mvn package	go build -o app.exe ./cmd/server/
mvn test	go test ./...
gradle dependencies	go mod tidy
需要 JVM 才能跑	編譯成原生二進位，零依賴