urlconnection.connect
时间: 2023-05-01 13:03:24 浏览: 61
'b'urlconnection.connect' 是 Java 中用来建立网络连接的方法。它会尝试连接指定的 URL,如果连接成功,则返回一个 HttpURLConnection 对象,可用于发送请求和接收响应。如果连接失败,则抛出异常。在调用该方法前,可以使用 setDoOutput/setDoInput 方法设置是否启用输出/输入,以及使用 setRequestMethod 方法设置请求方法。
相关问题
class ImageDownloader (private val url: String, private val imageView: ImageView, private val progressBar: ProgressBar) : Handler.Callback { private val handler = Handler(Looper.getMainLooper(), this) override fun handleMessage(msg: Message): Boolean { if (msg.what == 0) { imageView.setImageBitmap(msg.obj as Bitmap) progressBar.visibility = View.GONE } else if (msg.what == 1) { progressBar.progress = msg.arg1 } return true } fun download() { Thread { val bitmap = downloadImageFromUrl(url) handler.sendMessage(handler.obtainMessage(0, bitmap)) }.start() } private fun downloadImageFromUrl(url: String): Bitmap? { var bitmap: Bitmap? = null try { val urlConnection = URL(url).openConnection() urlConnection.connect() val inputStream = urlConnection.inputStream val totalSize = urlConnection.contentLength val data = ByteArray(1024) var downloadedSize = 0 var bufferLength: Int while (inputStream.read(data).also { bufferLength = it } != -1) { downloadedSize += bufferLength val progress = (downloadedSize * 100 / totalSize) handler.sendMessage(handler.obtainMessage(1, progress, 0)) bitmap = BitmapFactory.decodeByteArray(data, 0, bufferLength) } inputStream.close() } catch (e: Exception) { Log.e("ImageDownloader", "Error downloading image", e) } return bitmap } } 报出Process: com.example.imagedownloader, PID: 4842 java.lang.NullPointerException: null cannot be cast to non-null type android.graphics.Bitmap错误 修改代码
在 `downloadImageFromUrl` 函数中,应该将 `BitmapFactory.decodeByteArray` 转换成可空类型,以避免在无法解码字节数组时抛出 `NullPointerException`。修改后的代码如下:
```
private fun downloadImageFromUrl(url: String): Bitmap? {
var bitmap: Bitmap? = null
try {
val urlConnection = URL(url).openConnection()
urlConnection.connect()
val inputStream = urlConnection.inputStream
val totalSize = urlConnection.contentLength
val data = ByteArray(1024)
var downloadedSize = 0
var bufferLength: Int
while (inputStream.read(data).also { bufferLength = it } != -1) {
downloadedSize += bufferLength
val progress = (downloadedSize * 100 / totalSize)
handler.sendMessage(handler.obtainMessage(1, progress, 0))
bitmap = BitmapFactory.decodeByteArray(data, 0, bufferLength)?.let { it } // 加上安全转换
}
inputStream.close()
} catch (e: Exception) {
Log.e("ImageDownloader", "Error downloading image", e)
}
return bitmap
}
```
URLConnection co = url.openConnection(); co.setConnectTimeout(20000); co.connect();如何查看网页加载时间
可以通过Java代码来记录网页加载时间,具体代码如下:
```
long startTime = System.currentTimeMillis();
URLConnection co = url.openConnection();
co.setConnectTimeout(20000);
co.connect();
long endTime = System.currentTimeMillis();
long pageLoadTime = endTime - startTime;
System.out.println("该网页加载用时:" + pageLoadTime + "毫秒");
```
其中,`startTime` 记录开始时间,`endTime` 记录结束时间,`pageLoadTime` 则为网页加载时间,可以通过 `System.out.println` 输出到控制台。