期中考试 | 用Kotlin实现图片处理程序

git clone 之后，打开编译就报错，MultipleCompilationErrorsException 。把 gradle/wrapper/gradle-wrapper.properties 里面的 7.1 版本改成 7.2 之后重新编译就可以了。 有同样问题的同学可以参考一下。

// Image 添加方法，同时 去掉 pixels 的 private fun getHorArray(x: Int): Array<Color> { return pixels[x] } //// fun Image.flipHorizontal(): Image { for (i in (0 until this.height())) { this.getHorArray(i).reverse() } return this } fun Image.flipVertical(): Image { this.pixels.reverse() return this } fun Image.crop(startY: Int, startX: Int, width: Int, height: Int): Image { return Array(width - startY) { y -> Array(height - startX) { x -> Color(this.getPixel(x, y).rgb) } }.let { Image(it) } }

fun main() = runBlocking { File(BASE_PATH).mkdirs() downloadFile(URL, getPathFile("origin")) .loadImage() .also { it.flipVertical().writeToFile(getPathFile("vertical")) } .also { it.flipHorizontal().writeToFile(getPathFile("horizontal")) } .also { it.crop(0, 0, 100, 50).writeToFile(getPathFile("crop")) } delay(10L) }

图片下载功能 private val client = OkHttpClient.Builder() .build() /** * 挂起函数，以http的方式下载图片，保存到本地 */ suspend fun downloadImage(url: String, outputFile: File): Boolean = suspendCoroutine { con -> val request = Request.Builder() .url(url) .get() .build() client.newCall(request) .enqueue(object : Callback { override fun onFailure(call: Call, e: IOException) { e.printStackTrace() con.resume(false) } override fun onResponse(call: Call, response: Response) { if (response.isSuccessful) { response.body?.bytes()?.let { outputFile.writeBytes(it) } con.resume(true) } else { con.resume(false) } } }) } fun main() = runBlocking { val url = "http://img.netbian.com/file/2020/1202/smallaaa773e8cc9729977037e80b19f955891606922519.jpg" val file = File("${BASE_PATH}wallpaper.png") val success = downloadImage(url, file) println("Download file status is success：$success") }

// 先交作业，后看参考实现 // 图片处理 单测Case 较难实现，偷懒写本地肉眼看 /** * 写到本地，方便可看效果 */ fun Image.writeJPEG(outputFile: File): Boolean = ImageIO.write(BufferedImage(width(), height(), BufferedImage.TYPE_INT_RGB).apply { repeat(height) { y -> repeat(width) { x -> setRGB(x, y, getPixel(y, x).rgb) } } }, "JPEG", outputFile) /** * 图片裁切 */ fun Image.crop(startY: Int, startX: Int, width: Int, height: Int): Image = Array(height) { y -> Array(width) { x -> getPixel(y + startY, x + startX) } }.let { Image(it) } /** * 横向翻转图片 */ fun Image.flipHorizontal(): Image = Array(height()) { y -> Array(width()) { x -> getPixel(y, width() - x - 1) } }.let { Image(it) } /** * 纵向翻转图片 */ fun Image.flipVertical(): Image = Array(height()) { y -> Array(width()) { x -> getPixel(height() - y - 1, x) } }.let { Image(it) } /** * 挂起函数，以http的方式下载图片，保存到本地 */ suspend fun downloadImage(url: String, outputFile: File): Boolean = withContext(Dispatchers.IO) { OkHttpClient.Builder().build().run { newCall(Request.Builder().apply { url(url) get() }.build()).execute().run { if (!isSuccessful) { return@run false } return@run body?.byteStream()?.source()?.let { outputFile.sink().buffer().writeAll(it) > 0 } ?: false } } }

/** * 挂起函数，以http的方式下载图片，保存到本地 */ suspend fun downloadImage(url: String, outputFile: File) = withContext(Dispatchers.IO) { val client = OkHttpClient() val request = Request.Builder() .url(url) .build() val response = client .newCall(request) .execute() var size = 0L response.body?.byteStream()?.readAllBytes()?.let { bytes -> outputFile.writeBytes(bytes) size = bytes.size.toLong() } if (size == response.headersContentLength()) { return@withContext true } return@withContext false } /** * 主函数 */ fun main() = runBlocking { val url = "https://raw.githubusercontent.com/chaxiu/ImageProcessor/main/src/main/resources/images/android.png" val path = "./download.png" val success = downloadImage(url, File(path)) println(success) val image = loadImage(File(path)) println("Width = ${image.width()};Height = ${image.height()}") } 看到有同学使用 suspendCoroutine 函数处理，不知道和我这个方法比较有什么区别 👀

当然是要把第一部分和第二部分的内容结合起来啦： 首先自己创建一个获取图片的接口： @GetMapping("/{name}", produces = [MediaType.IMAGE_JPEG_VALUE]) fun picture(@PathVariable name: String): ByteArray { return pictureService.getPicture(name) } 然后用之前的KtCall发请求： @GET("/picture/mountain") fun image(): KtCall<ByteArray> suspend fun downloadImage() = runBlocking { val deferred = async { KtHttpProxy.create(ApiService::class.java) .image() .await() } println("still in progress") return@runBlocking deferred.await() }

使用系统自带的 api 下载文件 suspend fun downloadImage(url: String, outputFile: File): Boolean = withContext(Dispatchers.IO) { kotlin.runCatching { URL(url).openStream().use { outputFile.writeBytes(it.readAllBytes()) } } }.isSuccess