package com.example.springbootdemo.exception;

import com.example.springbootdemo.common.ResultCode;
import lombok.Getter;

@Getter
public class BusinessException extends RuntimeException {

    private final ResultCode resultCode;

    public BusinessException(ResultCode resultCode) {
        super(resultCode.getMessage());
        this.resultCode = resultCode;
    }
}

// ... imports ...
import com.example.springbootdemo.common.ResultCode;
import com.example.springbootdemo.exception.BusinessException;
import com.example.springbootdemo.entity.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;


@Service
@RequiredArgsConstructor
public class UserServiceImpl implements UserService {

    private final UserMapper userMapper;

    @Override
    public Long saveUser(UserEditDTO dto) {
        // 业务校验：检查用户名是否已存在
        User existingUser = userMapper.selectOne(new QueryWrapper<User>().lambda().eq(User::getUsername, dto.getUsername()));
        if (existingUser != null) {
            // 如果用户已存在，抛出自定义业务异常
            throw new BusinessException(ResultCode.UserAlreadyExists);
        }
        // ... 后续代码不变 ...
    }
    
    
    @Override
    public void updateUser(UserEditDTO dto) {
        // 1. 业务校验：断言要修改的用户必须存在
        User user = userMapper.selectById(dto.getId());
        if (user == null) {
            throw new BusinessException(ResultCode.UserNotFound);
        }

    }

    
    // ... 其他方法 ...
}

package com.example.springbootdemo.advice;

import com.example.springbootdemo.common.Result;
import com.example.springbootdemo.exception.BusinessException;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;

@Slf4j
@RestControllerAdvice(basePackages = "com.example.springbootdemo.controller")
public class GlobalExceptionHandler {

    /**
     * 专门处理我们自定义的 BusinessException
     */
    @ExceptionHandler(BusinessException.class)
    public ResponseEntity<Result<Void>> handleBusinessException(BusinessException ex) {
        log.error("业务异常: {}", ex.getMessage(), ex);
        // 对于业务异常，我们通常认为这是客户端的“错误”请求，所以返回 400 Bad Request
        // 响应体中包含我们预定义的业务错误码和消息
        return ResponseEntity
                .status(HttpStatus.BAD_REQUEST)
                .body(Result.error(ex.getResultCode()));
    }
}

// ... imports ...
import org.springframework.web.bind.MethodArgumentNotValidException;
import java.util.stream.Collectors;


@Slf4j
@RestControllerAdvice(basePackages = "com.example.springbootdemo.controller")
public class GlobalExceptionHandler {

    // ... 已有的 handleBusinessException 方法 ...

    /**
     * 专门处理由 @Validated 注解触发的参数校验异常
     */
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Result<Void>> handleValidationException(MethodArgumentNotValidException ex) {
        // 从异常中获取所有校验失败的信息，并拼接成一个字符串
        String message = ex.getBindingResult().getFieldErrors().stream()
                .map(fieldError -> fieldError.getField() + ": " + fieldError.getDefaultMessage())
                .collect(Collectors.joining("; "));
        
        log.warn("参数校验失败: {}", message);
        
        return ResponseEntity
                .status(HttpStatus.BAD_REQUEST)
                .body(Result.error(message));
    }
}

// ... imports ...

@Slf4j
@RestControllerAdvice(basePackages = "com.example.springbootdemo.controller")
public class GlobalExceptionHandler {

    // ... 已有的两个 ExceptionHandler ...

    /**
     * 兜底处理所有其他未被捕获的异常
     */
    @ExceptionHandler(Exception.class)
    public ResponseEntity<Result<Void>> handleUnknownException(Exception ex) {
        log.error("系统未知异常: {}", ex.getMessage(), ex);
        // 对于未知的系统异常，我们返回 500 Internal Server Error
        // 并使用一个通用的、模糊的错误提示，避免泄露服务器内部细节
        return ResponseEntity
                .status(HttpStatus.INTERNAL_SERVER_ERROR)
                .body(Result.error("系统异常，请联系管理员"));
    }
}

package com.example.springbootdemo.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**") // 对所有请求路径生效
                .allowedOrigins("http://localhost:5173") // 允许来自指定源的请求
                .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS") // 允许的方法
                .allowCredentials(true) // 允许发送 Cookie
                .maxAge(3600); // 预检请求的有效期，单位为秒
    }
}

// ... WebConfig 内容保持不变 ...
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/springboot-uploads/**")
            .addResourceLocations("file:" + uploadDir);
}

package com.example.springbootdemo.controller;

import cn.hutool.core.io.FileUtil;
import cn.hutool.core.util.IdUtil;
import com.example.springbootdemo.common.Result;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.tags.Tag;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Array;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

@Tag(name = "文件管理", description = "提供文件上传下载接口")
@RestController
@RequestMapping("/files")
public class FileController {
    @Value("${app.upload.dir}")
    private String uploadDir;

    @Operation(summary = "文件上传")
    @PostMapping("/upload")
    public Result<String> uploadFile(@RequestParam("file") MultipartFile file) throws IOException {
        if (file.isEmpty()) {
            return Result.error("文件名不能为空");
        }

        String originalFilename = file.getOriginalFilename(); // 获取原始文件名 如：test.png
        String extName = FileUtil.extName(originalFilename); // 获取文件扩展名 如：.png
        String uniqueId = IdUtil.fastSimpleUUID();
        String newFileName = uniqueId + "." + extName;

        // 定义文件存储的完整路径
        // 这里的File构造器接受两个参数：文件的父目录和文件名
        File destFile = new File(uploadDir, newFileName);
        // 使用 Hutool 将文件写入磁盘，它会自动创建父目录，无需手动判断
        FileUtil.writeBytes(file.getBytes(), destFile);
        return Result.success(newFileName);
    }


    @Operation(summary = "获取文件列表")
    @GetMapping("/list")
    public Result<List<String>> listFiles() {
        File uploadDirFile = new File(uploadDir);
        File[] files = uploadDirFile.listFiles();
        if (files == null) {
            return Result.success(Collections.emptyList());
        }
        List<String> filenames = Arrays.stream(files)
                .map(File::getName)
                .toList();

        return Result.success(filenames);
    }


    @Operation(summary = "文件下载（强制附件）")
    @GetMapping("/download/{filename}")
    public void downloadFile(@PathVariable String filename, HttpServletResponse response) throws IOException {
        File file = new File(uploadDir, filename);
        if (!file.exists()) {
            // 如果文件不存在，可以向 response 写入错误信息
            response.setStatus(HttpServletResponse.SC_NOT_FOUND);
            response.getWriter().write("File Not Found");
            return;
        }
        // 设置响应头
        response.reset();
        response.setContentType("application/octet-stream");
        // 对文件名进行URL编码，以支持中文等特殊字符
        String encodedFilename = URLEncoder.encode(filename, StandardCharsets.UTF_8.toString());
        response.setHeader("Content-Disposition", "attachment; filename=\"" + encodedFilename + "\"");

        // 【Hutool 核心优化】使用 Hutool 将文件内容写入到响应的输出流中
        // Hutool 会自动处理输入输出流的打开和关闭，非常安全
        FileUtil.writeToStream(file, response.getOutputStream());
    }
}