多线程文件下载简单实现(1)

1.Connection接口

public interface Connection {    /**     * @Author xuyangyang     * @Describe  给定开始和结束位置， 读取数据， 返回值是字节数组     * @Date 2017/6/7     * @Params      * @Return      */    byte[] read(int startPos, int endPos) throws IOException ;    /**     * @Author xuyangyang     * @Describe 得到数据内容的长度     * @Date 2017/6/7     * @Params     * @Return     */    int getContentLength();    /**     * @Author xuyangyang     * @Describe  关闭连接     * @Date 2017/6/7     * @Params     * @Return     */    void close();}

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2.ConnectionManager管理接口

public interface ConnectionManager {    /**     * @Author xuyangyang     * @Describe 给定一个url , 打开一个连接     * @Date 2017/6/7     * @Params      * @Return      */    Connection open(String url) throws ConnectionException;}

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3.实现ConnectionManager,根据url打开一个连接,返回Connection对象

public class ConnectionManagerImpl implements ConnectionManager {    @Override    public Connection open(String url) throws ConnectionException {        return new ConnectionImpl(url);    }}

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4.具体的实现类

public class ConnectionImpl implements Connection {    URL url;    static final int BUFFER_SIZE = 1024;    public ConnectionImpl(String _url) {        try {            url = new URL(_url);        } catch (MalformedURLException e) {            e.printStackTrace();        }    }    @Override    public byte[] read(int startPos, int endPos) throws IOException {        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();        httpURLConnection.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);        InputStream in = httpURLConnection.getInputStream();        byte[] bytes = new byte[BUFFER_SIZE];        int totalLen = endPos - startPos + 1;        ByteArrayOutputStream baos = new ByteArrayOutputStream();        while (baos.size() < totalLen) {            int len = in.read(bytes);            if (len < 0) {                break;            }            baos.write(bytes, 0, len);        }        if (baos.size() > totalLen) {            byte[] data = baos.toByteArray();            return Arrays.copyOf(data, totalLen);        }        return baos.toByteArray();    }    @Override    public int getContentLength() {        URLConnection con;        try {            con = url.openConnection();            return con.getContentLength();        } catch (IOException e) {            e.printStackTrace();        }        return -1;    }    @Override    public void close() {    }}

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5.简单的测试

public class ConnectionTest {    @Before    public void setUp() throws Exception {    }    @After    public void tearDown() throws Exception {    }    @Test    public void testContentLength() throws Exception{        ConnectionManager connMan = new ConnectionManagerImpl();        Connection conn = connMan.open("http://www.hinews.cn/pic/0/13/91/26/13912621_821796.jpg");        Assert.assertEquals(35470, conn.getContentLength());    }    @Test    public void testRead() throws Exception{        ConnectionManager connMan = new ConnectionManagerImpl();        Connection conn = connMan.open("http://www.hinews.cn/pic/0/13/91/26/13912621_821796.jpg");        byte[] data = conn.read(0, 35469);        Assert.assertEquals(35470, data.length);        data = conn.read(0, 1023);        Assert.assertEquals(1024, data.length);        data = conn.read(1024, 2023);        Assert.assertEquals(1000, data.length);        // 测试不充分，没有断言内容是否正确    }}