refactor multi-thread downloading

Author: Viscaria233

group01/895457260/code/src/download/FileDownloader.java

@@ -17,10 +17,9 @@ public class FileDownloader {
 	private final int[] completedThreadCount = new int[1];
 
 	/**
-	 * 下载目录见 <code>Config</code>
+	 * 下载一个url指向的文件，下载目录见 <code>Config</code>
+	 *
 	 * @see Config#targetDirectory
-	 * @see #setConnectionManager(ConnectionManager)
-	 * @see #setListener(DownloadListener)
 	 * @see #execute()
 	 */
 	public FileDownloader(String url) {
@@ -201,7 +200,7 @@ public void setListener(DownloadListener listener) {
 
 	/**
 	 *
-	 * @param manager 通过url，打开连接
+	 * @param manager 通过url打开连接
 	 * @see ConnectionManager#open(String)
 	 */
 	public void setConnectionManager(ConnectionManager manager) {

group01/895457260/code/src/download/impl/ConnectionImpl.java

@@ -12,19 +12,19 @@ public class ConnectionImpl implements Connection {
 	private InputStream inputStream;
 
 	ConnectionImpl(String url) throws ConnectionException {
-		init(url);
-	}
-
-	private void init(String url) {
 		try {
-			connection = new URL(url).openConnection();
-			inputStream = new BufferedInputStream(connection.getInputStream());
-			inputStream.mark(connection.getContentLength()); // 标记在开头
+			init(url);
 		} catch (IOException e) {
-			e.printStackTrace();
+			throw new ConnectionException();
 		}
 	}
 
+	private void init(String url) throws IOException {
+		connection = new URL(url).openConnection();
+		inputStream = new BufferedInputStream(connection.getInputStream());
+		inputStream.mark(connection.getContentLength()); // 标记在开头
+	}
+
 	@Override
 	public byte[] read(int startPos, int endPos) throws IOException {
 		inputStream.reset(); // reset回到标记处