通过JSON文件获取图片URL，下载并显示在布局中

1.AsyncTask来实现网络的异步加载

2.获取JSON数据的图片地址，在用图片地址去下载图片

3.把下载下来的图片保存在文件里

4.加载到布局上

遗留问题：缓存怎么处理？

JSON代码：

{"status":1,"img":
	[
		{
			"id":"1",
			"imageurl":"http://192.168.31.152/image/b1.jpg"			
		},
		{
			"id":"2",
			"imageurl":"http://192.168.31.152/image/b2.jpg"				
		},
		{
			"id":"3",
			"imageurl":"http://192.168.31.152/image/b3.jpg"			
		},
		{
			"id":"4",
			"imageurl":"http://h.hiphotos.baidu.com/news/q%3D100/sign=d38d087d5bdf8db1ba2e78643921dddb/9345d688d43f87942b2f41cbd71b0ef41ad53a06.jpg"	
		},
	]
}

新建一个Bean类用来存储对应的属性

public class UrlBean {

    public String imgUrl;

}

获取JSON数据的方法，并返回Bean对象

    /**
     * 获取Json数据
     *
     * @return
     */

    private List<UrlBean> getJsonData(String url) {
        List<UrlBean> lists = new ArrayList<>();

        try {
            String jsonString = readStream(new URL(imgURL).openStream());
            JSONObject jsonObject;
            UrlBean urlBean;
            try {
                jsonObject = new JSONObject(jsonString);
                JSONArray jsonArray = jsonObject.getJSONArray("img");
                for (int i = 0; i < jsonArray.length(); i++) {
                    jsonObject = jsonArray.getJSONObject(i);
                    urlBean = new UrlBean();
                    urlBean.imgUrl = jsonObject.getString("imageurl");
                    lists.add(urlBean);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return lists;
    }

    /**
     * 输入流-字符输入流 返回字符串
     * @param is
     * @return
     */
    private String readStream(InputStream is) {
        InputStreamReader isr;
        String result = "";
        try {
            String line = "";
            isr = new InputStreamReader(is, "utf-8");
            BufferedReader bufferedReader = new BufferedReader(isr);
            while ((line = bufferedReader.readLine()) != null) {
                result += line;
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

用两个异步加载的方法分别读取JSON和循环读取每一张图片（应该又更好的方法把）

    /**
     * 异步加载
     * @return
     */

    class MyAsyncTask extends AsyncTask<String, Void, List<UrlBean>> {

        @Override
        protected List<UrlBean> doInBackground(String... params) {
            return getJsonData(params[0]);//URL获取JSON数据
        }

        @Override
        protected void onPostExecute(List<UrlBean> urlBeans) {
            super.onPostExecute(urlBeans);
            for (int i = 0 ; i<urlBeans.size(); i++) {
                new MyImageAsyncTask().execute(urlBeans.get(i).imgUrl);
            }
        }
    }

    //通过没一个图片的地址请求一次网络得到图片
    class MyImageAsyncTask extends AsyncTask<String, Void, View>{

        @Override
        protected View doInBackground(String... params) {

            Bitmap bitmap = getBitmapFromURL(params[0]);
            ImageView imageView = getImageView(bitmap);
            return imageView;
        }

        @Override
        protected void onPostExecute(View view) {
            super.onPostExecute(view);
            views.add(view);
            if (views.size()>3){
                setlayoutImage(views);
            }
        }
    };

通过JSON里的每一个图片的地址，来获取Bitmap对象。在得到输入流时，做了存入SD卡操作

    private File shen;
    private File sdcard;
    private int x;  //笨方法，动态循环更改文件名
    public Bitmap getBitmapFromURL(String urlString){
        Bitmap bitmap;
        InputStream is = null;
        FileOutputStream fos;
        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            is = new BufferedInputStream(connection.getInputStream());
            bitmap = BitmapFactory.decodeStream(is);

            //直接把输入流存到SD卡里
            if (Environment.getExternalStorageState().equals(
                    Environment.MEDIA_MOUNTED)) {

                sdcard = Environment.getExternalStorageDirectory();
                shen = new File(sdcard, "ss/a" + x + ".jpg");
                x = x+1;
                Log.i("ccc",  "ss/"+urlString);
                fos = new FileOutputStream(shen);
                byte[] b = new byte[2 * 1024];
                int len;
                if (is != null) {
                    while ((len = is.read(b)) != -1) {
                        fos.write(b, 0, len);
                    }
                }
                //只做了下载图片，没做缓存，暂时还不知道怎么做
                //bitmap = BitmapFactory.decodeFile(shen.getAbsolutePath());
            }

            connection.disconnect();
            return bitmap;
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

Bitmap 返回 ImageView

   public ImageView getImageView(Bitmap bitmap) {
        ImageView imageView = new ImageView(this);
        imageView.setImageBitmap(bitmap);
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        return imageView;
    }

把图片加载到布局中（这里或许可以不用List对象的 得到一个图加载一个图）

    public void setlayoutImage(List<View> views){
        LinearLayout ll = (LinearLayout) findViewById(R.id.linear);
        for (int i = 0; i<views.size(); i++){
            ll.addView(views.get(i));
        }
    }