java EasyExcel面向Excel文档读写逻辑示例详解
目录
- 正文
- 1 快速上手
- 1.1 引入依赖
- 1.2 导入与导出
- 2 实现原理
- 2.1 @RequestExcel 与 @ResponseExcel 解析器
- 2.2 RequestMappingHandlerAdapter 后置处理器
- 3 总结
正文
EasyExcel
是一款由阿里开源的 Excel 处理工具。相较于原生的Apache POI
,它可以更优雅、快速地完成 Excel 的读写功能,同时更加地节约内存。
即使 EasyExcel 已经很优雅了,但面向 Excel 文档的读写逻辑几乎千篇一律,笔者索性将这些模板化的逻辑抽离出来,该组件已经发布到 maven 中央仓库,感兴趣的朋友可以体验一下。
1 快速上手
1.1 引入依赖
<dependency> <groupId>io.github.dk900912</groupId> <artifactId>easyexcel-spring-boot-starter</artifactId> <version>0.0.7</version> </dependency>
1.2 导入与导出
@RestController @RequestMapping(path = "/easyexcel") public class ExcelController { @PostMapping(path = "/v1/upload") public ResponseEntity<String> upload( @RequestExcel(sheets = { @Sheet(index = 0, headClazz = User.class, headRowNumber = 1), @Sheet(index = 1, headClazz = User.class, headRowNumber = 1), @Sheet(index = 2, headClazz = User.class, headRowNumber = 1) }) @Valid List<List<User>> users) { return ResponseEntity.ok("OK"); } @ResponseExcel( name="程序猿", sheets = { @Sheet(name = "sheet-0", headClazz = User.class), @Sheet(name = "sheet-1", headClazz = User.class), @Sheet(name = "sheet-2", headClazz = User.class) }, suffix = ExcelTypeEnum.XLSX) @GetMapping(path = "/v1/export") public List<List<User>> export() { List<User> data = Lists.newArrayList(); for (int i = 0; i < 10000; i++) { User user = User.builder().name("暴风赤红" + (i+1)) .birth(LocalDate.now()).address("江苏省苏州市科技城昆仑山路58号") .build(); data.add(user); } return ImmutableList.of(data, data, data); } @ResponseExcel(name="templates/程序猿.xlsx", scene = TEMPLATE) @GetMapping(path = "/v1/template") public void template() {} }
2 实现原理
一切 Java 程序都是基于 Thread 的,当一个 HTTP 请求到达后,Servlet Container 会从其线程池中捞出一个线程来处理该 HTTP 请求。具体地,该 HTTP 请求首先到达 Servlet Container 的FilterChain
中;然后,FilterChain 将该 HTTP 请求委派给DispatcherServlet
处理,而 DispatcherServlet 恰恰就是 Spring MVC 的门户。在 Spring MVC 中,所有 HTTP 请求都由 DispatcherServlet 进行路由分发。大致流程下图所示。
DispatcherServlet 在 HandlerMapping 的帮助下可以快速匹配到最终的 Controller,由于 Controller 大多由@RequestMapping
注解标注,那么RequestMappingHandlerMapping
最终脱颖而出。
RequestMappingHandlerMapping 会将 HTTP 请求映射到一个HandlerExecutionChain
实例中,每一个 HandlerExecutionChain 实例的内部维护了HandlerMethod
和List<HandlerInterceptor>
。
其中,HandlerMethod 实例持有一个Object
类型的 bean 变量和java.lang.reflect.Method
类型的 method 变量,bean 和 method 这俩成员变量组合起来最终可以确定究竟由哪一个 Controller 中的某一方法来处理当前 HTTP 请求。
此时已经知道目标方法了,那直接反射执行目标方法?是不可以的,因为通过反射来执行目标方法需要有参数才行,此外还需要对目标方法的执行结果进行加工处理。既然 HandlerMapping 没有解析请求体和处理目标执行结果的能力,只能再引入一层适配器了,它就是 HandlerAdapter。
在 Spring MVC 所提供的若干种 HandlerAdapter 中,能够适配 HandlerMethod 的只有RequestMappingHandlerAdapter
;
RequestMappingHandlerAdapter 实现了InitializingBean
接口,用于初始化HandlerMethodArgumentResolverComposite
类型的 argumentResolvers 成员变量和HandlerMethodReturnValueHandlerComposite
类型的 returnValueHandlers 成员变量,Composite 后缀表明这俩成员变量均是一种复合类,argumentResolvers 持有数十种HandlerMethodArgumentResolver
类型的方法参数解析器,而 returnValueHandlers 则持有数十种HandlerMethodReturnValueHandler
类型的方法返回值解析器。
重点来了!首先,我们需要一个实现 HandlerMethodArgumentResolver 接口的方法参数解析器,该解析器主要用于解析@RequestExcel
注解,以读取 Excel 文档;
此外,我们还需要一个实现 HandlerMethodReturnValueHandler 接口的方法返回值解析器,该解析器主要用于解析@ResponseExcel
注解,以将目标方法所返回的数据写入到 Excel 文档中;
最后,将这两个自定义的解析器分别添加到 RequestMappingHandlerAdapter 中的 argumentResolvers 与 returnValueHandlers 这俩成员变量中。
在 Spring MVC 中,由RequestResponseBodyMethodProcessor
负责处理@RequestBody
与@ResponseBody
注解。基于这一事实,笔者也没有单独设计两个解析器来分别应对 @RequestExcel 与 @ResponseExcel 注解,而是合二为一。
2.1 @RequestExcel 与 @ResponseExcel 解析器
public class RequestResponseExcelMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler { private final ResourceLoader resourceLoader; public RequestResponseExcelMethodProcessor(ResourceLoader resourceLoader) { this.resourceLoader = resourceLoader; } @Override public boolean supportsParameter(MethodParameter parameter) { return parameter.hasParameterAnnotation(RequestExcel.class); } @Override public boolean supportsReturnType(MethodParameter returnType) { return returnType.hasMethodAnnotation(ResponseExcel.class); } @Override public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { parameter = parameter.nestedIfOptional(); Object data = readWithMessageConverters(webRequest, parameter); validateIfNecessary(data, parameter); return data; } @Override public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception { // There is no need to render view mavContainer.setRequestHandled(true); writeWithMessageConverters(returnValue, returnType, webRequest); } // +----------------------------------------------------------------------------+ // | private method for read | // +----------------------------------------------------------------------------+ protected <T> Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter parameter) throws IOException, UnsatisfiedMethodSignatureException { validateArgParamOrReturnValueType(parameter); HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class); Assert.state(servletRequest != null, "No HttpServletRequest"); return readWithMessageConverters(servletRequest, parameter); } protected Object readWithMessageConverters(HttpServletRequest servletRequest, MethodParameter parameter) throws IOException { RequestExcelInfo requestExcelInfo = new RequestExcelInfo(parameter.getParameterAnnotation(RequestExcel.class)); InputStream inputStream; if (servletRequest instanceof MultipartRequest) { inputStream = ((MultipartRequest) servletRequest) .getMultiFileMap() .values() .stream() .flatMap(Collection::stream) .findFirst() .map(multipartFile -> { try { return multipartFile.getInputStream(); } catch (IOException e) { return null; } }) .get(); } else { inputStream = servletRequest.getInputStream(); } CollectorReadListener collectorReadListener = new CollectorReadListener(); try (ExcelReader excelReader = EasyExcel.read(inputStream).build()) { List<ReadSheet> readSheetList = requestExcelInfo.getSheetInfoList() .stream() .map(sheetInfo -> EasyExcel.readSheet(sheetInfo.getIndex()) .head(sheetInfo.getHeadClazz()) .registerReadListener(collectorReadListener) .build() ) .collect(Collectors.toList()); excelReader.read(readSheetList); } return collectorReadListener.groupByHeadClazz(); } protected void validateIfNecessary(Object data, MethodParameter parameter) throws ExcelCellContentNotValidException { if (parameter.hasParameterAnnotation(Validated.class) || parameter.hasParameterAnnotation(Valid.class)) { List<Object> flattenData = ((List<List<Object>>) data).stream() .flatMap(Collection::stream) .collect(Collectors.toList()); for (Object target : flattenData) { Set<ConstraintViolation<Object>> constraintViolationSet = ValidationUtil.validate(target); if (CollectionUtils.isNotEmpty(constraintViolationSet)) { String errorMsg = constraintViolationSet.stream() .map(ConstraintViolation::getMessage) .distinct() .findFirst() .get(); throw new ExcelCellContentNotValidException(errorMsg); } } } } // +----------------------------------------------------------------------------+ // | private method for write | // +----------------------------------------------------------------------------+ protected void writeWithMessageConverters(Object value, MethodParameter returnType, NativeWebRequest webRequest) throws IOException, HttpMessageNotWritableException, UnsatisfiedMethodSignatureException { HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class); Assert.state(response != null, "No HttpServletResponse"); ResponseExcelInfo responseExcelInfo = new ResponseExcelInfo(returnType.getMethodAnnotation(ResponseExcel.class)); final String fileName = responseExcelInfo.getName(); response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"); response.setCharacterEncoding(StandardCharsets.UTF_8.name()); if (TEMPLATE.equals(responseExcelInfo.getScene())) { response.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode( fileName.substring(fileName.indexOf("/") + 1), StandardCharsets.UTF_8.name())); BufferedInputStream bufferedInputStream = new BufferedInputStream(resourceLoader.getResource(CLASSPATH_URL_PREFIX + fileName).getInputStream()); BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(response.getOutputStream()); FileCopyUtils.copy(bufferedInputStream, bufferedOutputStream); } else { validateArgParamOrReturnValueType(returnType); response.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode( fileName, StandardCharsets.UTF_8.name()) + responseExcelInfo.getSuffix().getValue()); try (ExcelWriter excelWriter = EasyExcel.write(response.getOutputStream()).build()) { List<WriteSheet> writeSheetList = responseExcelInfo.getSheetInfoList() .stream() .map(sheetInfo -> EasyExcel.writerSheet(sheetInfo.getName()) .head(sheetInfo.getHeadClazz()) .build() ) .collect(Collectors.toList()); List<List<Object>> multiSheetData = (List<List<Object>>) value; for (int i = 0; i < writeSheetList.size(); i++) { WriteSheet writeSheet = writeSheetList.get(i); List<Object> singleSheetData = multiSheetData.get(i); excelWriter.write(singleSheetData, writeSheet); } } } } // +----------------------------------------------------------------------------+ // | common private method | // +----------------------------------------------------------------------------+ private void validateArgParamOrReturnValueType(MethodParameter target) throws UnsatisfiedMethodSignatureException { try { ResolvableType resolvableType = ResolvableType.forMethodParameter(target); if (!List.class.isAssignableFrom(resolvableType.resolve())) { throw new UnsatisfiedMethodSignatureException( "@RequestExcel or @ResponseExcel Must Be Annotated With List<List<>>"); } if (!List.class.isAssignableFrom(resolvableType.getGeneric(0).resolve())) { throw new UnsatisfiedMethodSignatureException( "@RequestExcel or @ResponseExcel Must Be Annotated With List<List<>>"); } } catch (Exception exception) { throw new UnsatisfiedMethodSignatureException( "@RequestExcel or @ResponseExcel Must Be Annotated With List<List<>>"); } } }
2.2 RequestMappingHandlerAdapter 后置处理器
public class RequestMappingHandlerAdapterPostProcessor implements BeanPostProcessor, PriorityOrdered, ResourceLoaderAware { private ResourceLoader resourceLoader; @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (!supports(bean)) { return bean; } RequestMappingHandlerAdapter requestMappingHandlerAdapter = (RequestMappingHandlerAdapter) bean; List<HandlerMethodArgumentResolver> argumentResolvers = requestMappingHandlerAdapter.getArgumentResolvers(); List<HandlerMethodReturnValueHandler> returnValueHandlers = requestMappingHandlerAdapter.getReturnValueHandlers(); Assert.notEmpty(argumentResolvers, "RequestMappingHandlerAdapter's argument resolver is empty, this is illegal state"); Assert.notEmpty(returnValueHandlers, "RequestMappingHandlerAdapter's return-value handler is empty, this is illegal state"); List<HandlerMethodArgumentResolver> copyArgumentResolvers = new ArrayList<>(argumentResolvers); RequestResponseExcelMethodProcessor argumentResolver4RequestExcel = new RequestResponseExcelMethodProcessor(null); copyArgumentResolvers.add(0, argumentResolver4RequestExcel); requestMappingHandlerAdapter.setArgumentResolvers(Collections.unmodifiableList(copyArgumentResolvers)); List<HandlerMethodReturnValueHandler> copyReturnValueHandlers = new ArrayList<>(returnValueHandlers); RequestResponseExcelMethodProcessor returnValueHandler4ResponseExcel = new RequestResponseExcelMethodProcessor(resourceLoader); copyReturnValueHandlers.add(0, returnValueHandler4ResponseExcel); requestMappingHandlerAdapter.setReturnValueHandlers(Collections.unmodifiableList(copyReturnValueHandlers)); return requestMappingHandlerAdapter; } @Override public int getOrder() { return Ordered.LOWEST_PRECEDENCE; } @Override public void setResourceLoader(ResourceLoader resourceLoader) { this.resourceLoader = resourceLoader; } private boolean supports(Object bean) { return bean instanceof RequestMappingHandlerAdapter; } }
3 总结
目前该版本仅支持针对单个 Excel 文档的导入与导出(多Sheet是支持的哈),所以由 @RequestExcel 注解修饰的方法参数必须是一个List<List<>>类型,而由 @RequestExcel 注解修饰的方法返回类型也必须是一个List<List<>>类型,否则将抛出UnsatisfiedMethodSignatureException
类型的自定义异常。
坦白来说,该组件的设计初衷只是为了帮助大家从公式化、模板化的Excel 读写逻辑中解放出来,从而专注于核心业务逻辑的开发,并不是为了增强 EasyExcel,后续也不会朝着这一方向演进。
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