Android攻城狮读取了JSON实现图文混排

通过inputStream读取网页信息。
我们定义一个方法用于读取输入流：
public String readStream(InputStream is){
        InputStreamReader isr;
        String result="";
        try {
            String line="";
            isr = new InputStreamReader(is,"utf-8");
            BufferedReader br = new BufferedReader(isr);
            while((line = br.readLine())!=null){
                result += line;
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
其中，传进参数InputStream is 是字节流，InputStreamReader(is,"utf-8")将字节流转化为字符流，再通过BufferedReader封装，以BufferedReader形式读取出来，最终拼接到字符串result里面。这样就完成了整个数据的读取。
既然读取了JSON字符串，接下来把它转换为我们想要的数据。

格式转换：将 JSON 字符串转换为我们想要的数据。这里仅仅先实现字符串的获取。其中 Log.d("xys",jsonString)是把json字符串以日志的形式打印出来。
InputStream is由 new URL(url).openStream()获得。此句功能与url.openConnection.getInputStream()相同，可根据URL直接联网获取网络数据，简单粗暴！返回值类型为InputStream。
另外，不要忘记在配置文件中添加网络权限：<uses-permission android:name="android.permission.INTERNET"></uses>

public class MainActivity extends ActionBarActivity {
    private ListView listView;
    private static String URL = "http://www.imooc.com/api/teacher?type=4&num=30";
    NewAsyncTask task;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        listView = (ListView) findViewById(R.id.listtView1);
        task = new NewAsyncTask();
        task.execute(URL);
    }

    // 实现网络异步访问
    class NewAsyncTask extends AsyncTask<String, Void, List<NewsBean>> {
        @Override
        protected void onPostExecute(List<NewsBean> result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            NewAdapter adapter = new NewAdapter(MainActivity.this, result);
            listView.setAdapter(adapter);

        }

        @Override
        protected List<NewsBean> doInBackground(String... params) {
            // TODO Auto-generated method stub

            return getJsonData(params[0]);
        }

        // 将URL对应的Jeson格式数据转化为我们所封装的NewsBean对象
        private List<NewsBean> getJsonData(String URL) {
            // TODO Auto-generated method stub
            List<NewsBean> newsBeanlist = new ArrayList<NewsBean>();
            try {
                String jString = readstream(new java.net.URL(URL).openStream());
                // Log.i("--->>", jString);
                JSONObject jsonObject;
                NewsBean newsBean;
                try {
                    jsonObject = new JSONObject(jString);
                    JSONArray jsonArray = jsonObject.getJSONArray("data");
                    for (int i = 0; i < jsonArray.length(); i++) {
                        jsonObject = jsonArray.getJSONObject(i);
                        newsBean = new NewsBean();
                        newsBean.newsiconUrl = jsonObject.getString("picSmall");
                        newsBean.newsTitle = jsonObject.getString("name");
                        newsBean.newsContent = jsonObject
                                .getString("description");
                        newsBeanlist.add(newsBean);
                    }
 
                } catch (JSONException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return newsBeanlist;
        }

        // 通过InputStream解析返回数据
        private String readstream(InputStream iStream) {
            InputStreamReader isr;
            String result = "";
            try {
                String line = "";
                isr = new InputStreamReader(iStream, "utf-8");
                BufferedReader br = new BufferedReader(isr);
                try {
                    while ((line = br.readLine()) != null) {
                        result += line;

                    }
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            } catch (UnsupportedEncodingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return result;

        }

    }
}

------------------------------------------------------------

public class NewAdapter extends BaseAdapter {
    private List<NewsBean> mList;
    private LayoutInflater mInflater;
    private ImageLoader mImageLoader;

    public NewAdapter(Context context, List<NewsBean> data) {
        // TODO Auto-generated constructor stub
        mList = data;
        mInflater = LayoutInflater.from(context);
        mImageLoader = new ImageLoader();
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return mList.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return mList.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        viewHolder vHolder = null;
        if (convertView == null) {
            vHolder = new viewHolder();
            convertView = mInflater.inflate(R.layout.item_layout, null);
            vHolder.tvicon = (ImageView) convertView
                    .findViewById(R.id.imageview);
            vHolder.tvconten = (TextView) convertView
                    .findViewById(R.id.content);
            vHolder.tvtitle = (TextView) convertView.findViewById(R.id.title);

            convertView.setTag(vHolder);

        } else {
            vHolder = (viewHolder) convertView.getTag();
        }
        vHolder.tvicon.setImageResource(R.drawable.ic_launcher);

        String url = mList.get(position).newsiconUrl;
        vHolder.tvicon.setTag(url);
        // 多线程加载
        // new
        // ImageLoader().showImageByThread(vHolder.tvicon,mList.get(position).newsiconUrl);
        // 异步加载图片
        mImageLoader.ShowImageByAsycnTask(vHolder.tvicon, url);

        vHolder.tvtitle.setText(mList.get(position).newsTitle);
        vHolder.tvconten.setText(mList.get(position).newsContent);
        return convertView;
    }

    class viewHolder {
        public TextView tvtitle, tvconten;
        public ImageView tvicon;

    }

}

package com.example.zy_item;

public class NewsBean {
public String newsiconUrl;
public String newsTitle;
public String newsContent;
}

public class ImageLoader {
    private String murl;
    private ImageView mimageView;
    // 创建Cache
    private LruCache<String, Bitmap> mCache;

    public ImageLoader() {
        // TODO Auto-generated constructor stub
        // 获取最大可用内存
        int maxMemory = (int) Runtime.getRuntime().maxMemory();
        int CacheSize = maxMemory / 4;
        mCache=new LruCache<String, Bitmap>(CacheSize){
            
            @Override
            protected int sizeOf(String key, Bitmap value) {
                // TODO Auto-generated method stub
                return  value.getByteCount();
            }
        };
        

    }

    // 增加到缓存
    public void addBitmapToCache(String url, Bitmap bitmap) {
        if (getBitmapFromCache(url) == null) {
            mCache.put(url, bitmap);
        }
    }

    // 从缓存中获取数据
    public Bitmap getBitmapFromCache(String url) {
        return mCache.get(url);
    }

    private Handler mhandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            super.handleMessage(msg);
            if (mimageView.getTag().equals(murl))

                mimageView.setImageBitmap((Bitmap) msg.obj);
        }

    };

    // 多线程加载
    public void showImageByThread(ImageView imageView, final String url) {

        mimageView = imageView;
        murl = url;
        new Thread() {

            @Override
            public void run() {
                // TODO Auto-generated method stub
                super.run();
                Bitmap bitmap = getBitmapFromURL(url);
                Message message = Message.obtain();
                message.obj = bitmap;
                mhandler.sendMessage(message);
            }

        }.start();

    }

    public Bitmap getBitmapFromURL(String urlString) {
        Bitmap bitmap;
        InputStream iStream = null;

        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url
                    .openConnection();

            iStream = new BufferedInputStream(connection.getInputStream());
            bitmap = BitmapFactory.decodeStream(iStream);
            connection.disconnect();
            return bitmap;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {

            try {
                iStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

        return null;

    }

    // 基于AsycnTask加载：
    public void ShowImageByAsycnTask(ImageView imageView, String url) {
        // 从缓存中取出对应图片
        Bitmap bitmap = getBitmapFromCache(url);
        // 如果缓存中没有，那么必须去下载
        if (bitmap == null) {
            new NewAsyncTask(imageView, url).execute(url);
        }

        else {
            imageView.setImageBitmap(bitmap);
        }
    }

    private class NewAsyncTask extends AsyncTask<String, Void, Bitmap> {
        private ImageView mImageView;
        private String murl;

        public NewAsyncTask(ImageView imageView, String url) {
            // TODO Auto-generated constructor stub
            mImageView = imageView;
            murl = url;
        }
  
        @Override
        protected Bitmap doInBackground(String... params) {
            // TODO Auto-generated method stub
            // 从网络获取图片
            String ur =params[0];
            Bitmap bitmap = getBitmapFromURL(ur);
            if (bitmap != null) {
                // 将不在缓存的图片加入缓存
                addBitmapToCache(ur, bitmap);
            }
            return  bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap result) {
            // TODO Auto-generated method stub
            super.onPostExecute(result);
            if (mImageView.getTag().equals(murl))

                mImageView.setImageBitmap(result);
        }

    }

}

Android 异步加载的总结
1. 通过异步加载，避免阻塞UI线程，从而实现了网络的异步访问。这是基础，也是 Android 要求我们这么做的。
2. 通过 LruCache，将已经下载的图片放到内存中，以一个缓存避免多次重复的下载，提高用户的体验。当然，这里只介绍了内存缓存，我们还可以使用 DiskLruCache ，将内存中的图片保存到硬盘中，保存到存储器中，做为一个持久化的缓存，这也称作“二级缓存”。而内存缓存便叫做“一级缓存”。
3. 通过判断 ListView 的滑动状态，决定什么时候该加载图片，什么时候不该加载图片，而让ListView平滑地去滚动。在这一点上我们是通过对 ListView 的滑动状态的监听，去实现这样的操作，将加载图片的控制权由 getView() 转移到我们的滑动事件，从而让复杂的 ListView 也能实现流畅的异步加载。
4. 不仅仅是 ListView ,任何控件都可以使用异步加载，这里以 ListView 作为例子的原因是因为它比较常用。异步加载不仅仅用于获取网络图片，所有的耗时操作我们都可以认为是异步加载，通过异步的方式，去将这些耗时操作与主线程分开，从而提升用户体验，这也是异步加载的核心所在。