设计模式实战运用之模板方法模式

1. 通用文件上传服务

/**  * 上传图片  *  * @param multipartFile    文件  * @param uploadPathPrefix 上传路径前缀  * @return  */  
public UploadPictureResult uploadPicture(MultipartFile multipartFile, String uploadPathPrefix) {  // 校验图片  validPicture(multipartFile);  // 图片上传地址  String uuid = RandomUtil.randomString(16);  String originFilename = multipartFile.getOriginalFilename();  String uploadFilename = String.format("%s_%s.%s", DateUtil.formatDate(new Date()), uuid,  FileUtil.getSuffix(originFilename));  String uploadPath = String.format("/%s/%s", uploadPathPrefix, uploadFilename);  File file = null;  try {  // 创建临时文件  file = File.createTempFile(uploadPath, null);  multipartFile.transferTo(file);  // 上传图片  PutObjectResult putObjectResult = cosManager.putPictureObject(uploadPath, file);  ImageInfo imageInfo = putObjectResult.getCiUploadResult().getOriginalInfo().getImageInfo();  // 封装返回结果  UploadPictureResult uploadPictureResult = new UploadPictureResult();  int picWidth = imageInfo.getWidth();  int picHeight = imageInfo.getHeight();  double picScale = NumberUtil.round(picWidth * 1.0 / picHeight, 2).doubleValue();  uploadPictureResult.setPicName(FileUtil.mainName(originFilename));  uploadPictureResult.setPicWidth(picWidth);  uploadPictureResult.setPicHeight(picHeight);  uploadPictureResult.setPicScale(picScale);  uploadPictureResult.setPicFormat(imageInfo.getFormat());  uploadPictureResult.setPicSize(FileUtil.size(file));  uploadPictureResult.setUrl(cosClientConfig.getHost() + "/" + uploadPath);  return uploadPictureResult;  } catch (Exception e) {  log.error("图片上传到对象存储失败", e);  throw new BusinessException(ErrorCode.SYSTEM_ERROR, "上传失败");  } finally {  this.deleteTempFile(file);  }  
}  /**  * 校验文件  *  * @param multipartFile multipart 文件  */  
public void validPicture(MultipartFile multipartFile) {  ThrowUtils.throwIf(multipartFile == null, ErrorCode.PARAMS_ERROR, "文件不能为空");  // 1. 校验文件大小  long fileSize = multipartFile.getSize();  final long ONE_M = 1024 * 1024L;  ThrowUtils.throwIf(fileSize > 2 * ONE_M, ErrorCode.PARAMS_ERROR, "文件大小不能超过 2M");  // 2. 校验文件后缀  String fileSuffix = FileUtil.getSuffix(multipartFile.getOriginalFilename());  // 允许上传的文件后缀  final List<String> ALLOW_FORMAT_LIST = Arrays.asList("jpeg", "jpg", "png", "webp");  ThrowUtils.throwIf(!ALLOW_FORMAT_LIST.contains(fileSuffix), ErrorCode.PARAMS_ERROR, "文件类型错误");  
}  /**  * 删除临时文件  */  
public void deleteTempFile(File file) {  if (file == null) {  return;  }  // 删除临时文件  boolean deleteResult = file.delete();  if (!deleteResult) {  log.error("file delete error, filepath = {}", file.getAbsolutePath());  }  
}

2.URL 上传

• 支持输入一个URL，从URL 获取图片。再走通用文件上传服务的相似流程。

1. 图片下载：后端服务通过指定的远程 URL 将图片下载至本地临时存储。在 Java 项目中，可以借助 Hutool 工具包中的 HttpUtil.downloadFile 方法。

2. 图片校验：与验证本地文件类似，需对图片的格式、大小等进行校验。

   传统的校验方式通常是先将文件下载到本地，再对本地文件进行校验。然而，这种方法可能会消耗较多的资源。实际上，我们可以先对 URL 进行校验
   首先，检查 URL 字符串本身的合法性，确保其为一个有效的 URL 地址。此外，可以利用 HEAD 请求来获取 URL 对应文件的元信息（如文件大小、格式等）。HEAD 请求仅返回 HTTP 响应头信息，而不会下载文件的实际内容，从而显著减少网络流量的消耗。
   需要注意的是，此处应避免使用 GET 请求，因为它会获取完整的文件内容。

以下是一个使用 Java 实现 HEAD 请求的代码示例，并解释其工作原理：

代码示例

import java.net.HttpURLConnection;
import java.net.URL;public class HeadRequestExample {public static void main(String[] args) {try {// 目标 URLString imageUrl = "https://example.com/path/to/image.jpg";// 创建 URL 对象URL url = new URL(imageUrl);// 打开 HTTP 连接HttpURLConnection connection = (HttpURLConnection) url.openConnection();// 设置请求方法为 HEADconnection.setRequestMethod("HEAD");// 发送请求并获取响应码int responseCode = connection.getResponseCode();if (responseCode == HttpURLConnection.HTTP_OK) {// 获取文件大小（Content-Length）long fileSize = connection.getContentLengthLong();System.out.println("文件大小: " + fileSize + " bytes");// 获取文件类型（Content-Type）String fileType = connection.getContentType();System.out.println("文件类型: " + fileType);// 获取其他元信息（如最后修改时间）String lastModified = connection.getHeaderField("Last-Modified");System.out.println("最后修改时间: " + lastModified);} else {System.out.println("请求失败，响应码: " + responseCode);}// 关闭连接connection.disconnect();} catch (Exception e) {e.printStackTrace();}}
}

代码解释

1. URL 对象：

   • 使用 URL 类创建一个指向目标资源的 URL 对象。

2. HTTP 连接：

   • 使用 HttpURLConnection 打开一个 HTTP 连接。

3. 设置请求方法：

   • 通过 setRequestMethod("HEAD") 将请求方法设置为 HEAD，表示我们只需要响应头信息。

4. 发送请求：

   • 调用 getResponseCode() 发送请求并获取响应码（如 200 表示成功，404 表示资源未找到）。

5. 获取元信息：

   • 文件大小：通过 getContentLengthLong() 获取 Content-Length 头信息，表示文件大小。
   • 文件类型：通过 getContentType() 获取 Content-Type 头信息，表示文件类型（如 image/jpeg）。
   • 其他信息：通过 getHeaderField() 获取其他头信息，如 Last-Modified（最后修改时间）。

6. 关闭连接：

   • 使用 disconnect() 关闭连接，释放资源。

输出示例

假设目标 URL 是一个有效的图片文件，输出可能如下：

文件大小: 102400 bytes
文件类型: image/jpeg
最后修改时间: Wed, 01 Jan 2025 12:00:00 GMT

优点

• HEAD 请求比 GET 请求更高效，因为它不会下载文件内容，只获取元信息，适合用于校验文件是否符合要求（如大小、类型等），避免不必要的下载。

代码抽象

• 仔细观察代码就可以发现上述两个上传文件的方法，一个参数是文件对象，一个参数是文件URL，其他步骤流程保持一致。可以采用模板方法设计模式进行抽象。

1） 最简单的做法是，直接把参数类型设置为 Object。然后在子类中再进行强转返回。

/*** 图片上传模板*/
@Slf4j
public abstract class PictureUploadTemplate {@Resourceprivate CosClientConfig cosClientConfig;@Resourceprivate CosManager cosManager;/*** 上传图片** @param inputSource      文件* @param uploadPathPrefix 上传路径前缀* @return*/public UploadPictureResult uploadPicture(Object inputSource, String uploadPathPrefix) {// 1. 校验图片validPicture(inputSource);// 2. 图片上传地址String uuid = RandomUtil.randomString(16);String originalFilename = getOriginFilename(inputSource);// 自己拼接文件上传路径，而不是使用原始文件名称，可以增强安全性String uploadFilename = String.format("%s_%s.%s", DateUtil.formatDate(new Date()), uuid,FileUtil.getSuffix(originalFilename));String uploadPath = String.format("/%s/%s", uploadPathPrefix, uploadFilename);File file = null;try {// 3. 创建临时文件，获取文件到服务器file = File.createTempFile(uploadPath, null);// 处理文件来源processFile(inputSource, file);// 4. 上传图片到对象存储PutObjectResult putObjectResult = cosManager.putPictureObject(uploadPath, file);// 5. 获取图片信息对象，封装返回结果ImageInfo imageInfo = putObjectResult.getCiUploadResult().getOriginalInfo().getImageInfo();// 获取到图片处理结果ProcessResults processResults = putObjectResult.getCiUploadResult().getProcessResults();List<CIObject> objectList = processResults.getObjectList();if (CollUtil.isNotEmpty(objectList)) {// 获取压缩之后得到的文件信息CIObject compressedCiObject = objectList.get(0);// 缩略图默认等于压缩图CIObject thumbnailCiObject = compressedCiObject;// 有生成缩略图，才获取缩略图if (objectList.size() > 1) {thumbnailCiObject = objectList.get(1);}// 封装压缩图的返回结果return buildResult(originalFilename, compressedCiObject, thumbnailCiObject, imageInfo);}return buildResult(originalFilename, file, uploadPath, imageInfo);} catch (Exception e) {log.error("图片上传到对象存储失败", e);throw new BusinessException(ErrorCode.SYSTEM_ERROR, "上传失败");} finally {// 6. 临时文件清理this.deleteTempFile(file);}}/*** 校验输入源（本地文件或 URL）*/protected abstract void validPicture(Object inputSource);/*** 获取输入源的原始文件名*/protected abstract String getOriginFilename(Object inputSource);/*** 处理输入源并生成本地临时文件*/protected abstract void processFile(Object inputSource, File file) throws Exception;/*** 封装返回结果** @param originalFilename   原始文件名* @param compressedCiObject 压缩后的对象* @param thumbnailCiObject 缩略图对象* @param imageInfo 图片信息* @return*/private UploadPictureResult buildResult(String originalFilename, CIObject compressedCiObject, CIObject thumbnailCiObject,ImageInfo imageInfo) {// 计算宽高int picWidth = compressedCiObject.getWidth();int picHeight = compressedCiObject.getHeight();double picScale = NumberUtil.round(picWidth * 1.0 / picHeight, 2).doubleValue();// 封装返回结果UploadPictureResult uploadPictureResult = new UploadPictureResult();// 设置压缩后的原图地址uploadPictureResult.setUrl(cosClientConfig.getHost() + "/" + compressedCiObject.getKey());uploadPictureResult.setPicName(FileUtil.mainName(originalFilename));uploadPictureResult.setPicSize(compressedCiObject.getSize().longValue());uploadPictureResult.setPicWidth(picWidth);uploadPictureResult.setPicHeight(picHeight);uploadPictureResult.setPicScale(picScale);uploadPictureResult.setPicFormat(compressedCiObject.getFormat());uploadPictureResult.setPicColor(imageInfo.getAve());// 设置缩略图地址uploadPictureResult.setThumbnailUrl(cosClientConfig.getHost() + "/" + thumbnailCiObject.getKey());// 返回可访问的地址return uploadPictureResult;}/*** 封装返回结果** @param originalFilename* @param file* @param uploadPath* @param imageInfo        对象存储返回的图片信息* @return*/private UploadPictureResult buildResult(String originalFilename, File file, String uploadPath, ImageInfo imageInfo) {// 计算宽高int picWidth = imageInfo.getWidth();int picHeight = imageInfo.getHeight();double picScale = NumberUtil.round(picWidth * 1.0 / picHeight, 2).doubleValue();// 封装返回结果UploadPictureResult uploadPictureResult = new UploadPictureResult();uploadPictureResult.setUrl(cosClientConfig.getHost() + "/" + uploadPath);uploadPictureResult.setPicName(FileUtil.mainName(originalFilename));uploadPictureResult.setPicSize(FileUtil.size(file));uploadPictureResult.setPicWidth(picWidth);uploadPictureResult.setPicHeight(picHeight);uploadPictureResult.setPicScale(picScale);uploadPictureResult.setPicFormat(imageInfo.getFormat());uploadPictureResult.setPicColor(imageInfo.getAve());// 返回可访问的地址return uploadPictureResult;}/*** 清理临时文件** @param file*/public void deleteTempFile(File file) {if (file == null) {return;}// 删除临时文件boolean deleteResult = file.delete();if (!deleteResult) {log.error("file delete error, filepath = {}", file.getAbsolutePath());}}
}

2） 使用泛型。

/*** 使用泛型实现的图片上传模板* * 这种方式通过在类定义时声明类型参数T，使得整个模板类及其抽象方法都能针对具体的输入源类型进行编译时的类型检查，* 增强了代码的类型安全性，并且避免了使用Object类型可能导致的类型转换问题。*/
@Slf4j
public abstract class PictureUploadTemplate<T> {@Resourceprivate CosClientConfig cosClientConfig;@Resourceprivate CosManager cosManager;/*** 上传图片* * @param inputSource      输入源，类型由子类确定，如 File、URL 等* @param uploadPathPrefix 上传路径前缀* @return*/public UploadPictureResult uploadPicture(T inputSource, String uploadPathPrefix) {// 校验图片validPicture(inputSource);// 生成唯一标识和上传文件名String uuid = RandomUtil.randomString(16);String originalFilename = getOriginFilename(inputSource);String uploadFilename = String.format("%s_%s.%s", DateUtil.formatDate(new Date()), uuid,FileUtil.getSuffix(originalFilename));String uploadPath = String.format("/%s/%s", uploadPathPrefix, uploadFilename);File file = null;try {// 创建临时文件file = File.createTempFile(uploadPath, null);// 处理输入源，生成本地临时文件processFile(inputSource, file);// 上传临时文件到对象存储PutObjectResult putObjectResult = cosManager.putPictureObject(uploadPath, file);// 获取上传后图片的相关信息ImageInfo imageInfo = putObjectResult.getCiUploadResult().getOriginalInfo().getImageInfo();ProcessResults processResults = putObjectResult.getCiUploadResult().getProcessResults();List<CIObject> objectList = processResults.getObjectList();if (CollUtil.isNotEmpty(objectList)) {// 获取压缩图和缩略图信息CIObject compressedCiObject = objectList.get(0);CIObject thumbnailCiObject = compressedCiObject;if (objectList.size() > 1) {thumbnailCiObject = objectList.get(1);}return buildResult(originalFilename, compressedCiObject, thumbnailCiObject, imageInfo);}return buildResult(originalFilename, file, uploadPath, imageInfo);} catch (Exception e) {log.error("图片上传到对象存储失败", e);throw new BusinessException(ErrorCode.SYSTEM_ERROR, "上传失败");} finally {// 清理临时文件deleteTempFile(file);}}/*** 校验输入源* * @param inputSource 输入源，类型由子类确定*/protected abstract void validPicture(T inputSource);/*** 获取输入源的原始文件名* * @param inputSource 输入源，类型由子类确定* @return 原始文件名*/protected abstract String getOriginFilename(T inputSource);/*** 处理输入源并生成本地临时文件* * @param inputSource 输入源，类型由子类确定* @param file        临时文件* @throws Exception*/protected abstract void processFile(T inputSource, File file) throws Exception;/*** 封装返回结果（压缩图和缩略图处理情况）*/private UploadPictureResult buildResult(String originalFilename, CIObject compressedCiObject, CIObject thumbnailCiObject,ImageInfo imageInfo) {int picWidth = compressedCiObject.getWidth();int picHeight = compressedCiObject.getHeight();double picScale = NumberUtil.round(picWidth * 1.0 / picHeight, 2).doubleValue();UploadPictureResult uploadPictureResult = new UploadPictureResult();uploadPictureResult.setUrl(cosClientConfig.getHost() + "/" + compressedCiObject.getKey());uploadPictureResult.setPicName(FileUtil.mainName(originalFilename));uploadPictureResult.setPicSize(compressedCiObject.getSize().longValue());uploadPictureResult.setPicWidth(picWidth);uploadPictureResult.setPicHeight(picHeight);uploadPictureResult.setPicScale(picScale);uploadPictureResult.setPicFormat(compressedCiObject.getFormat());uploadPictureResult.setPicColor(imageInfo.getAve());uploadPictureResult.setThumbnailUrl(cosClientConfig.getHost() + "/" + thumbnailCiObject.getKey());return uploadPictureResult;}/*** 封装返回结果（只处理单张图片上传，无压缩、缩略图生成情况）*/private UploadPictureResult buildResult(String originalFilename, File file, String uploadPath, ImageInfo imageInfo) {int picWidth = imageInfo.getWidth();int picHeight = imageInfo.getHeight();double picScale = NumberUtil.round(picWidth * 1.0 / picHeight, 2).doubleValue();UploadPictureResult uploadPictureResult = new UploadPictureResult();uploadPictureResult.setUrl(cosClientConfig.getHost() + "/" + uploadPath);uploadPictureResult.setPicName(FileUtil.mainName(originalFilename));uploadPictureResult.setPicSize(FileUtil.size(file));uploadPictureResult.setPicWidth(picWidth);uploadPictureResult.setPicHeight(picHeight);uploadPictureResult.setPicScale(picScale);uploadPictureResult.setPicFormat(imageInfo.getFormat());uploadPictureResult.setPicColor(imageInfo.getAve());return uploadPictureResult;}/*** 清理临时文件*/public void deleteTempFile(File file) {if (file == null) {return;}boolean deleteResult = file.delete();if (!deleteResult) {log.error("file delete error, filepath = {}", file.getAbsolutePath());}}
}

总结

• 使用 Object 类型：适用于输入源类型不确定或多样化的场景，代码简单直接，但缺乏类型安全性，容易在运行时出现类型转换错误。

• 使用泛型：适用于输入源类型明确的场景，提供了编译时的类型检查，增强了代码的类型安全性和可读性，但增加了代码的复杂性。

适用场景

• 使用 Object 类型：适合在输入源类型不确定、多样化或需要兼容老旧代码的场景下使用。

• 使用泛型：适合在输入源类型明确、需要类型安全性和代码可读性的场景下使用