Android基于HttpURLConnection的异步下载图片

来源：互联网发布：钢结构详图软件编辑：程序博客网时间：2024/05/21 15:47

总所周知在Android6.0以后抛弃了对HttpClient的支持，提倡使用HttpURLConnection来网络请求，今天要用的就是使用HttpURLConnection做的一个异步任务下载图片的例子，不罗嗦，上代码：

我这里有一张网络图片的地址

    private String image_Path = "http://e.hiphotos.baidu.com/image/pic/item/2fdda3cc7cd98d10b510fdea233fb80e7aec9021.jpg";

然后开始我们的异步任务之旅

public class MyTask extends AsyncTask<String ,Void,Bitmap>{    @Override    protected void onPostExecute(Bitmap bitmap) {        super.onPostExecute(bitmap);        iv_img.setImageBitmap(bitmap);    }    @Override    protected Bitmap doInBackground(String... params) {        URL url=null;        InputStream is=null;        Bitmap bitmap=null;        try{            //设置图片的路径            url=new URL(params[0]);            //开启连接            HttpURLConnection conn= (HttpURLConnection) url.openConnection();            //设置超时的时间            conn.setConnectTimeout(5000);            //设置请求方式为GET            conn.setRequestMethod("GET");            //响应码为200则返回成功            if(conn.getResponseCode()==200){                //获取连接的输入流即图片的输入流                is=conn.getInputStream();                //将流转换为Bitmap                bitmap=BitmapFactory.decodeStream(is);                is.close();            }        }        catch (Exception e){            e.printStackTrace();        }finally {            try {                //关闭流                if (is != null) {                    is.close();                }            } catch (Exception e) {                e.printStackTrace();            }        }        return bitmap;    }}

注释已经很详细不细说

下面就开始使用了

由于简单我就直接在Activity的Oncreate方法中调用

new MyTask().execute(image_Path);

导致一个简单的异步任务下载图片的例子就完成了，下面我要做的事使用HttpURLconnection下载图片并缓存到本地

public class MainActivity extendsActivity {  
   
    privateContext mContext;  
    privateImageView image;  
    // 加载成功 
    privatestatic final int LOAD_SUCCESS = 1; 
    // 加载失败 
    privatestatic final int LOAD_ERROR = -1; 
    // 用于异步的显示图片 
    privateHandler handler = newHandler() {  
        publicvoid handleMessage(Message msg) { 
   
            switch(msg.what) {  
            //下载成功 
            caseLOAD_SUCCESS:  
                // 获取图片的文件对象 
                File file =new File(Environment.getExternalStorageDirectory(),"pic.jpg");  
                FileInputStream fis =null;  
                try{  
                    fis =new FileInputStream(file); 
                    Bitmap bitmap = BitmapFactory.decodeStream(fis); 
                    image.setImageBitmap(bitmap); 
   
                }catch (FileNotFoundException e) { 
                    e.printStackTrace(); 
                } 
   
                break; 
                //下载失败 
            caseLOAD_ERROR:  
   
                Toast.makeText(mContext,"加载失败", 0).show(); 
   
                break; 
            } 
   
        }; 
    }; 
   
    @Override 
    protectedvoid onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        mContext =this;  
        setContentView(R.layout.activity_main); 
        image = (ImageView) findViewById(R.id.image); 
    } 
   
    // Button的点击事件 
    publicvoid show(View view) { 
        // 开启新的线程用于下载图片 
        newThread(new Runnable() {  
            publicvoid run() {  
   
                getPicture(); 
            } 
        }).start(); 
   
    } 
   
    //下载图片的主方法 
    privatevoid getPicture() {  
           
        URL url =null;  
        InputStream is =null;  
        FileOutputStream fos =null;  
        try{  
            //构建图片的url地址 
            url =new URL("http://avatar.csdn.net/C/6/8/1_bz419927089.jpg"); 
            //开启连接 
            HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
            //设置超时的时间，5000毫秒即5秒 
            conn.setConnectTimeout(5000); 
            //设置获取图片的方式为GET 
            conn.setRequestMethod("GET"); 
            //响应码为200，则访问成功 
            if(conn.getResponseCode() == 200) { 
                //获取连接的输入流，这个输入流就是图片的输入流 
                is = conn.getInputStream(); 
                //构建一个file对象用于存储图片 
                File file =new File(Environment.getExternalStorageDirectory(),"pic.jpg");  
                fos =new FileOutputStream(file); 
                intlen = 0; 
                byte[] buffer =new byte[1024]; 
                //将输入流写入到我们定义好的文件中 
                while((len = is.read(buffer)) != -1) { 
                    fos.write(buffer,0, len);  
                } 
                //将缓冲刷入文件 
                fos.flush(); 
                //告诉handler，图片已经下载成功 
                handler.sendEmptyMessage(LOAD_SUCCESS); 
            } 
        }catch (Exception e) { 
            //告诉handler，图片已经下载失败 
            handler.sendEmptyMessage(LOAD_ERROR); 
            e.printStackTrace(); 
        }finally {  
            //在最后，将各种流关闭 
            try{  
                if(is != null) { 
                    is.close(); 
                } 
                if(fos != null) { 
                    fos.close(); 
                } 
            }catch (Exception e) { 
                handler.sendEmptyMessage(LOAD_ERROR); 
                e.printStackTrace(); 
            } 
        } 
    } 
   
}

到此基于HttpURLconnection的下载图片的例子结束。

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