Android 文件下载

demo下载地址 http://download.youkuaiyun.com/detail/h9911/8385923

其实不管是java还是android，都可以把输入输出流归为字节流和字符串流两种，一般的文字传输属于字符串流，而图片或者文件则属于字节流。

至于什么是字符串流和字节流，请查阅其他资料

废话不多说，直接上代码

记住先在AndroidManifest.xml中添加权限

    <uses-permission android:name="android.permission.INTERNET" />

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

package org.hpg.weather.download;

import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;


public class MainActivity extends ActionBarActivity {
    private static final String TAG = "MainActivity";
    String downloadUrl = "http://www.baidu.com/link?url=jg03OiD0qdTvFXqDAVPIN5DEnHjZbmC1obcgd1cZEKbDVLuWqCneKfp0TFLjdA7-7jok_S_Xcr2cuC898SDawODBDRHjQthP7PmAedG6srK";
    String picUrl ="http://img01.mifile.cn/images/accs/xmjsb_11.jpg";
    private Button downloadButton;
    private ProgressBar progressBar ;
    private int length = 0;
    private TextView percentView ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        downloadButton = (Button) findViewById(R.id.download);
        percentView = (TextView) findViewById(R.id.percent);
        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        progressBar.setProgress(0);

        downloadButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        download();
                    }
                }).start();
            }
        });
    }


    //下载具体操作
    private void download() {
        int contentLength = 0;
        try {
            URL url = new URL(downloadUrl);
            //打开连接
            URLConnection conn = url.openConnection();
            //打开输入流
            InputStream is = conn.getInputStream();
            //获得长度
            contentLength = conn.getContentLength();
            Log.e(TAG, "contentLength = " + contentLength);
            //创建文件夹 MyDownLoad，在存储卡下
            String dirName = Environment.getExternalStorageDirectory() + "/MyDownLoad/";
            File file = new File(dirName);
            //不存在创建
            if (!file.exists()) {
                file.mkdir();
            }
            //下载后的文件名
            String fileName = dirName + "qq.apk";
            File file1 = new File(fileName);
            if (file1.exists()) {
                file1.delete();
            }
            //创建字节流
            byte[] bs = new byte[1024];
            int len;
            OutputStream os = new FileOutputStream(fileName);
            //写数据
            while ((len = is.read(bs)) != -1) {
                length  =length + len;
                os.write(bs, 0, len);
                Message message = handler.obtainMessage();

                message.arg1 = 100 * length/contentLength;
                handler.sendMessage(message);
            }
            //完成后关闭流
            Log.e(TAG, "download-finish");
            os.close();
            is.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    //更新UI
    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            Log.e(TAG,msg.arg1+"");
            progressBar.setProgress(msg.arg1);
            percentView.setText(msg.arg1+"%");
        }
    };
}

下面一个是后来的版本

        String[] name = mUrl.split("/");
        File file = new File(mPath);
//        //如果已经下载直接打开在外部已经判断
//        if (file.exists()) {
//            mHandler.onSuccess(file);
//            return;
//        }
        try {
            URL url = new URL(mUrl);
            HttpURLConnection connection = (HttpURLConnection)
                    url.openConnection();
            connection.setRequestMethod("GET");
            //是否允许输入
            connection.setDoInput(true);
            //是否允许输出
            connection.setDoOutput(false);
            connection.setUseCaches(false);
            connection.setConnectTimeout(5000);
            connection.setReadTimeout(5000);
            //实现连接
            connection.connect();

            Log.e(TAG, "connection.getResponseCode()=" + connection.getResponseCode());
            //连接失败
            if (connection.getResponseCode() != 200) {
                if (mHandler != null) {
                    mHandler.onFailed();
                    connection.disconnect();
                }
                return;
            }
            if (connection.getResponseCode() == 200) {
                InputStream is = connection.getInputStream();
                //以下为下载操作
                byte[] bytes = new byte[1];
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                BufferedOutputStream bos = new BufferedOutputStream(baos);
                int len = is.read(bytes);
                Log.e(TAG, len + "");
                while (len > 0) {
                    bos.write(bytes);
                    len = is.read(bytes);
                }
                bos.close();

                FileOutputStream fos = new FileOutputStream(file);
                fos.write(baos.toByteArray());
                fos.close();
                //关闭网络连接
                if (mHandler != null) {
                    mHandler.onSuccess(file);
                }
                connection.disconnect();
                Log.e(TAG, "下载完成");
            }
        } catch (IOException e) {
            // TODO: handle exception
            e.printStackTrace();
        }