首先，我应该提一下，我试图在互联网上找到一个解决方案2天甚至更多，所以如果你想把我链接到另一个帖子，我很可能已经看过了。现在出现问题：
当我尝试下载图像时，使用某些链接我的代码可以正常工作，但有些会产生错误，例如，此链接会出错（以及我尝试从cdn.discordapp.com获取的所有其他链接）： https://cdn.discordapp.com/attachments/235200958974394368/256888406645145602/output.jpg
在您查看代码之前，我还应该提一下它使用外部API，但您仍然可以理解其中的大部分内容，此外，我的URL始终是图片网址。
这是我的代码：
try {
url = new URL(event.getMessage().getContent().substring(12));
openConnection = url.openConnection();
String userCredentials = "username:password";
String basicAuth = "Basic " + new String(new Base64().encode(userCredentials.getBytes()));
openConnection.setRequestProperty ("Authorization", basicAuth);
openConnection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0");
openConnection.setRequestProperty("Request Method", "POST");
// openConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
openConnection.setRequestProperty("Content-Language", "en-US");
openConnection.setUseCaches(false);
openConnection.setDoInput(true);
openConnection.setDoOutput(true);
if(openConnection.getContentLength() > 8000000) {
event.getChannel().sendMessage(event.getAuthor().getAsMention()+" file size is too big.").queue();
check = false;
}
} catch (Exception e) {
event.getChannel().sendMessage("Couldn't create a connection to the link, please recheck the link.").queue();
check = false;
e.printStackTrace();
}
if(check) {
BufferedImage img = null;
try {
InputStream in = new BufferedInputStream(url.openStream());
ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int n = 0;
while (-1 != (n=in.read(buf)))
{
out.write(buf, 0, n);
}
out.close();
in.close();
byte[] response = out.toByteArray();
img = ImageIO.read(new ByteArrayInputStream(response));
} catch (Exception e) {
event.getChannel().sendMessage(event.getAuthor().getAsMention()+" couldn't read an image from this link.").queue();
e.printStackTrace();
}
JPEGImageWriteParam jpegParams = new JPEGImageWriteParam(null);
jpegParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpegParams.setCompressionQuality(0.1f);
File file = new File("output.jpg");
try {
final ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next();
writer.setOutput(new FileImageOutputStream(file));
writer.write(null, new IIOImage(img, null, null), jpegParams);
event.getChannel().sendFile(file, null).queue();
file.delete();
} catch (IOException e) {
event.getChannel().sendMessage("Couldn't create/send the output image.").queue();
e.printStackTrace();
}
}
这是带有错误的堆栈跟踪（您可以忽略此行[23:21:06] [Fatal] [JDA]: One of the EventListeners had an uncaught exception及其中的任何内容）：
` java.io.IOException: Server returned HTTP response code: 403 for URL: https://cdn.discordapp.com/attachments/235200958974394368/256888406645145602/output.jpg
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source)
at java.net.URL.openStream(Unknown Source)
at discordBot.Jpegify.execute(Jpegify.java:73)
at discordBot.Christina.onMessageReceived(Christina.java:163)
at net.dv8tion.jda.core.hooks.ListenerAdapter.onEvent(ListenerAdapter.java:316)
at net.dv8tion.jda.core.hooks.InterfacedEventManager.handle(InterfacedEventManager.java:64)
at net.dv8tion.jda.core.handle.MessageCreateHandler.handleDefaultMessage(MessageCreateHandler.java:129)
at net.dv8tion.jda.core.handle.MessageCreateHandler.handleInternally(MessageCreateHandler.java:51)
at net.dv8tion.jda.core.handle.SocketHandler.handle(SocketHandler.java:38)
at net.dv8tion.jda.core.requests.WebSocketClient.handleEvent(WebSocketClient.java:665)
at net.dv8tion.jda.core.requests.WebSocketClient.onTextMessage(WebSocketClient.java:339)
at com.neovisionaries.ws.client.ListenerManager.callOnTextMessage(ListenerManager.java:352)
at com.neovisionaries.ws.client.ReadingThread.callOnTextMessage(ReadingThread.java:262)
at com.neovisionaries.ws.client.ReadingThread.callOnTextMessage(ReadingThread.java:240)
at com.neovisionaries.ws.client.ReadingThread.handleTextFrame(ReadingThread.java:965)
at com.neovisionaries.ws.client.ReadingThread.handleFrame(ReadingThread.java:748)
at com.neovisionaries.ws.client.ReadingThread.main(ReadingThread.java:110)
at com.neovisionaries.ws.client.ReadingThread.run(ReadingThread.java:66)
[23:21:06] [Fatal] [JDA]: One of the EventListeners had an uncaught exception
[23:21:06] [Fatal] [JDA]: Encountered an exception:
[23:21:06] [Fatal] [JDA]: java.lang.IllegalArgumentException: image == null!
at javax.imageio.IIOImage.<init>(Unknown Source)
at discordBot.Jpegify.execute(Jpegify.java:99)
at discordBot.Christina.onMessageReceived(Christina.java:163)
at net.dv8tion.jda.core.hooks.ListenerAdapter.onEvent(ListenerAdapter.java:316)
at net.dv8tion.jda.core.hooks.InterfacedEventManager.handle(InterfacedEventManager.java:64)
at net.dv8tion.jda.core.handle.MessageCreateHandler.handleDefaultMessage(MessageCreateHandler.java:129)
at net.dv8tion.jda.core.handle.MessageCreateHandler.handleInternally(MessageCreateHandler.java:51)
at net.dv8tion.jda.core.handle.SocketHandler.handle(SocketHandler.java:38)
at net.dv8tion.jda.core.requests.WebSocketClient.handleEvent(WebSocketClient.java:665)
at net.dv8tion.jda.core.requests.WebSocketClient.onTextMessage(WebSocketClient.java:339)
at com.neovisionaries.ws.client.ListenerManager.callOnTextMessage(ListenerManager.java:352)
at com.neovisionaries.ws.client.ReadingThread.callOnTextMessage(ReadingThread.java:262)
at com.neovisionaries.ws.client.ReadingThread.callOnTextMessage(ReadingThread.java:240)
at com.neovisionaries.ws.client.ReadingThread.handleTextFrame(ReadingThread.java:965)
at com.neovisionaries.ws.client.ReadingThread.handleFrame(ReadingThread.java:748)
at com.neovisionaries.ws.client.ReadingThread.main(ReadingThread.java:110)
at com.neovisionaries.ws.client.ReadingThread.run(ReadingThread.java:66)`
当然，非常感谢任何帮助，对于长篇文章感到抱歉，这个问题真的让我感到紧张......
答案 0 :(得分：2)
我明白了。你需要做几件事。首先，您需要在URLConnection上设置用户代理。然后你需要在URLConnection上打开openConnection。最后，如果您之前从URL获取流，则实际上需要从URLConnection获取getInputStream，因为这是您设置用户代理的位置。
这是我的代码，它的工作原理。将其复制并粘贴到名为Test.java的新文件中并尝试运行它。注意我注释掉了文件删除，因此您实际上可以看到文件下载
将它与您的活动和频道结合使用现在取决于您，祝您好运。
import java.awt.image.BufferedImage;
import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
import javax.imageio.stream.FileImageOutputStream;
public class Test {
public static void main(String[] args) throws MalformedURLException, IOException {
URL url = new URL("http://cdn.discordapp.com/attachments/235200958974394368/256888406645145602/output.jpg");
URLConnection openConnection = url.openConnection();
boolean check = true;
try {
openConnection.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11");
openConnection.connect();
if (openConnection.getContentLength() > 8000000) {
System.out.println(" file size is too big.");
check = false;
}
} catch (Exception e) {
System.out.println("Couldn't create a connection to the link, please recheck the link.");
check = false;
e.printStackTrace();
}
if (check) {
BufferedImage img = null;
try {
InputStream in = new BufferedInputStream(openConnection.getInputStream());
ByteArrayOutputStream out = new ByteArrayOutputStream();
byte[] buf = new byte[1024];
int n = 0;
while (-1 != (n = in.read(buf))) {
out.write(buf, 0, n);
}
out.close();
in.close();
byte[] response = out.toByteArray();
img = ImageIO.read(new ByteArrayInputStream(response));
} catch (Exception e) {
System.out.println(" couldn't read an image from this link.");
e.printStackTrace();
}
JPEGImageWriteParam jpegParams = new JPEGImageWriteParam(null);
jpegParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
jpegParams.setCompressionQuality(0.1f);
File file = new File("output.jpg");
try {
final ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next();
writer.setOutput(new FileImageOutputStream(file));
writer.write(null, new IIOImage(img, null, null), jpegParams);
// event.getChannel().sendFile(file, null).queue();
// file.delete();
} catch (IOException e) {
System.out.println("Couldn't create/send the output image.");
e.printStackTrace();
}
}
}
}