spring boot 渲染文件下载 by kotlin

字符串输出文件

   fun renderFile(fileName: String, data: String): ResponseEntity<InputStreamResource> {
        return ResponseEntity.ok()
                .headers(fileHeaders(fileName))
                .contentLength(data.length.toLong())
                .body(InputStreamResource(data.byteInputStream()))
    }

    private fun fileHeaders(fileName: String): HttpHeaders {
        val headers = HttpHeaders()
        headers.add("Cache-Control", "no-cache, no-store, must-revalidate")
        headers.add("Content-Disposition", "attachment; filename=\"$fileName\"")
        headers.add("Pragma", "no-cache")
        headers.add("Expires", "0")
        return headers
    }

输出 excel 文件

当手动拼 csv 文件字符串，再通过上面的方法输出的文件在 windows 上会乱码，输出的文件是给编辑的，要保证在 Excel 中打开没有问题才行，最简单可靠的办法就是引入专门的 csv lib 包来处理了

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-csv</artifactId>
            <version>1.5</version>
        </dependency>

代码如下

    //返回文件路径
    fun statistic(fileName: String): String {

        val filePath = "${System.getProperty("java.io.tmpdir")}/$fileName"
        val writer = FileWriter(filePath)
        //这个是写 utf8 bom 文件的头，不加的话 excel 打开文件的中文就是乱码
        writer.write(String(byteArrayOf(0xEF.toByte(), 0xBB.toByte(), 0xBF.toByte())))

        val csvPrinter = CSVFormat.EXCEL.withHeader("公众号", "数据量", "有效数据").print(writer)

        val infoMap = wechatDao.countByAuthor().map { it.author to it.num }.toMap()
        val importInfoMap = wechatDao.countImportedByAuthor().map { it.author to it.num }.toMap()

        infoMap.entries.forEach({ csvPrinter.printRecord(it.key, it.value, importInfoMap[it.key] ?: 0) })

        csvPrinter.printRecord("----- 统计 -----", infoMap.values.sum(), importInfoMap.values.sum())

        writer.flush()
        writer.close()
        log.info("微信统计写入文件 $filePath")
        return filePath
    }

Controller 中调用

    @GetMapping("/wechat/statistic")
    fun statistic(): ResponseEntity<InputStreamResource> {
        val dataStr = LocalDate.now().toString()
        val fileName = "wechat_$dataStr.csv"
        val filePath = wechatService.statistic(fileName)

        return ResponseEntity.ok()
                .headers(fileHeaders(fileName))
                .body(InputStreamResource(FileInputStream(filePath)))
    }

kotlin 真是越用越觉得爽