add backend

backend/src/main/java/com/yoyuzh/common/ApiResponse.java

@@ -0,0 +1,16 @@
+package com.yoyuzh.common;
+
+public record ApiResponse<T>(int code, String msg, T data) {
+
+    public static <T> ApiResponse<T> success(T data) {
+        return new ApiResponse<>(0, "success", data);
+    }
+
+    public static ApiResponse<Void> success() {
+        return new ApiResponse<>(0, "success", null);
+    }
+
+    public static ApiResponse<Void> error(ErrorCode errorCode, String msg) {
+        return new ApiResponse<>(errorCode.getCode(), msg, null);
+    }
+}

backend/src/main/java/com/yoyuzh/common/BusinessException.java

@@ -0,0 +1,15 @@
+package com.yoyuzh.common;
+
+public class BusinessException extends RuntimeException {
+
+    private final ErrorCode errorCode;
+
+    public BusinessException(ErrorCode errorCode, String message) {
+        super(message);
+        this.errorCode = errorCode;
+    }
+
+    public ErrorCode getErrorCode() {
+        return errorCode;
+    }
+}

backend/src/main/java/com/yoyuzh/common/ErrorCode.java

@@ -0,0 +1,18 @@
+package com.yoyuzh.common;
+
+public enum ErrorCode {
+    UNKNOWN(1000),
+    NOT_LOGGED_IN(1001),
+    PERMISSION_DENIED(1002),
+    FILE_NOT_FOUND(1003);
+
+    private final int code;
+
+    ErrorCode(int code) {
+        this.code = code;
+    }
+
+    public int getCode() {
+        return code;
+    }
+}

backend/src/main/java/com/yoyuzh/common/GlobalExceptionHandler.java

@@ -0,0 +1,51 @@
+package com.yoyuzh.common;
+
+import jakarta.validation.ConstraintViolationException;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.access.AccessDeniedException;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+@Slf4j
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(BusinessException.class)
+    public ResponseEntity<ApiResponse<Void>> handleBusinessException(BusinessException ex) {
+        HttpStatus status = switch (ex.getErrorCode()) {
+            case NOT_LOGGED_IN -> HttpStatus.UNAUTHORIZED;
+            case PERMISSION_DENIED -> HttpStatus.FORBIDDEN;
+            case FILE_NOT_FOUND -> HttpStatus.NOT_FOUND;
+            default -> HttpStatus.BAD_REQUEST;
+        };
+        return ResponseEntity.status(status).body(ApiResponse.error(ex.getErrorCode(), ex.getMessage()));
+    }
+
+    @ExceptionHandler({MethodArgumentNotValidException.class, ConstraintViolationException.class})
+    public ResponseEntity<ApiResponse<Void>> handleValidationException(Exception ex) {
+        return ResponseEntity.badRequest().body(ApiResponse.error(ErrorCode.UNKNOWN, ex.getMessage()));
+    }
+
+    @ExceptionHandler(AccessDeniedException.class)
+    public ResponseEntity<ApiResponse<Void>> handleAccessDenied(AccessDeniedException ex) {
+        return ResponseEntity.status(HttpStatus.FORBIDDEN)
+                .body(ApiResponse.error(ErrorCode.PERMISSION_DENIED, "没有权限访问该资源"));
+    }
+
+    @ExceptionHandler(BadCredentialsException.class)
+    public ResponseEntity<ApiResponse<Void>> handleBadCredentials(BadCredentialsException ex) {
+        return ResponseEntity.status(HttpStatus.UNAUTHORIZED)
+                .body(ApiResponse.error(ErrorCode.NOT_LOGGED_IN, "用户名或密码错误"));
+    }
+
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<ApiResponse<Void>> handleUnknown(Exception ex) {
+        log.error("Unhandled exception", ex);
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                .body(ApiResponse.error(ErrorCode.UNKNOWN, "服务器内部错误"));
+    }
+}

backend/src/main/java/com/yoyuzh/common/PageResponse.java

@@ -0,0 +1,6 @@
+package com.yoyuzh.common;
+
+import java.util.List;
+
+public record PageResponse<T>(List<T> items, long total, int page, int size) {
+}