android异步下载图片缓存到sdcard

从网络上加载XML资源，其中包括图片，我们要做的解析XML里面的数据，并且把图片缓存到本地一个cache目录里面，并且用一个自定义的Adapter去填充到LIstView：
对象类

public class Contact {        int id;        String image;        String name;                 public Contact() {                super();        }        public Contact(int id, String image, String name) {                this.id = id;                this.image = image;                this.name = name;        }        public int getId() {                return id;        }        public void setId(int id) {                this.id = id;        }        public String getImage() {                return image;        }        public void setImage(String image) {                this.image = image;        }        public String getName() {                return name;        }        public void setName(String name) {                this.name = name;        }         }

service类

public class ContactService {         /*         * 从服务器上获取数据         */        public List<Contact> getContactAll() throws Exception {                List<Contact> contacts = null;                String Parth = "http://10.0.2.2:8080/AsyncTaskTest/list.xml";                URL url = new URL(Parth);                HttpURLConnection conn = (HttpURLConnection) url.openConnection();                conn.setConnectTimeout(30000);                conn.setReadTimeout(30000);                conn.setRequestMethod("GET");                if (conn.getResponseCode() == HttpURLConnection.HTTP_OK) {                        InputStream is = conn.getInputStream();                        // 这里获取数据直接放在XmlPullParser里面解析                        contacts = xmlParser(is);                        return contacts;                } else {                        return null;                }        }         // 这里并没有下载图片下来，而是把图片的地址保存下来了        private List<Contact> xmlParser(InputStream is) throws Exception {                List<Contact> contacts = null;                Contact contact = null;                XmlPullParser parser = Xml.newPullParser();                parser.setInput(is, "UTF-8");                int eventType = parser.getEventType();                while ((eventType = parser.next()) != XmlPullParser.END_DOCUMENT) {                        switch (eventType) {                        case XmlPullParser.START_TAG:                                if (parser.getName().equals("contacts")) {                                        contacts = new ArrayList<Contact>();                                } else if (parser.getName().equals("contact")) {                                        contact = new Contact();                                        contact.setId(Integer.valueOf(parser.getAttributeValue(0)));                                } else if (parser.getName().equals("name")) {                                        contact.setName(parser.nextText());                                } else if (parser.getName().equals("image")) {                                        contact.setImage(parser.getAttributeValue(0));                                }                                break;                         case XmlPullParser.END_TAG:                                if (parser.getName().equals("contact")) {                                        contacts.add(contact);                                }                                break;                        }                }                return contacts;        }         /*         * 从网络上获取图片，如果图片在本地存在的话就直接拿，如果不存在再去服务器上下载图片         * 这里的path是图片的地址         */        public Uri getImageURI(String path, File cache) throws Exception {                String name = MD5.getMD5(path) + path.substring(path.lastIndexOf("."));                File file = new File(cache, name);                // 如果图片存在本地缓存目录，则不去服务器下载                 if (file.exists()) {                        return Uri.fromFile(file);//Uri.fromFile(path)这个方法能得到文件的URI                } else {                        // 从网络上获取图片                        URL url = new URL(path);                        HttpURLConnection conn = (HttpURLConnection) url.openConnection();                        conn.setConnectTimeout(5000);                        conn.setRequestMethod("GET");                        conn.setDoInput(true);                        if (conn.getResponseCode() == 200) {                                 InputStream is = conn.getInputStream();                                FileOutputStream fos = new FileOutputStream(file);                                byte[] buffer = new byte[1024];                                int len = 0;                                while ((len = is.read(buffer)) != -1) {                                        fos.write(buffer, 0, len);                                }                                is.close();                                fos.close();                                // 返回一个URI对象                                return Uri.fromFile(file);                        }                }                return null;        }}

自定义Adapter

public class ImageAdapter extends BaseAdapter {         protected static final int SUCCESS_GET_IMAGE = 0;        private Context context;        private List<Contact> contacts;        private File cache;        private LayoutInflater mInflater;         // 自己定义的构造函数        public ImageAdapter(Context context, List<Contact> contacts, File cache) {                this.context = context;                this.contacts = contacts;                this.cache = cache;                 mInflater = (LayoutInflater) context                                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);        }         @Override        public int getCount() {                return contacts.size();        }         @Override        public Object getItem(int position) {                return contacts.get(position);        }         @Override        public long getItemId(int position) {                return position;        }         @Override        public View getView(int position, View convertView, ViewGroup parent) {                // 1获取item,再得到控件                // 2 获取数据                // 3绑定数据到item                View view = null;                if (convertView != null) {                        view = convertView;                } else {                        view = mInflater.inflate(R.layout.item, null);                }                 ImageView iv_header = (ImageView) view.findViewById(R.id.imageView);                TextView tv_name = (TextView) view.findViewById(R.id.textView);                 Contact contact = contacts.get(position);                                 // 异步的加载图片 (线程池 + Handler ) ---> AsyncTask                asyncloadImage(iv_header, contact.image);                                 tv_name.setText(contact.name);                 return view;        }                 private void asyncloadImage(ImageView iv_header, String path) {                ContactService service = new ContactService();                AsyncImageTask task = new AsyncImageTask(service, iv_header);                task.execute(path);        }         private final class AsyncImageTask extends AsyncTask<String, Integer, Uri> {                 private ContactService service;                private ImageView iv_header;                 public AsyncImageTask(ContactService service, ImageView iv_header) {                        this.service = service;                        this.iv_header = iv_header;                }                 // 后台运行的子线程子线程                @Override                protected Uri doInBackground(String... params) {                        try {                                return service.getImageURI(params[0], cache);                        } catch (Exception e) {                                e.printStackTrace();                        }                        return null;                }                 // 这个放在在ui线程中执行                @Override                protected void onPostExecute(Uri result) {                        super.onPostExecute(result);                        // 完成图片的绑定                        if (iv_header != null && result != null) {                                iv_header.setImageURI(result);                        }                }        }}

public class MainActivity extends Activity {        protected static final int SUCCESS_GET_CONTACT = 0;        private ListView mListView;        private ImageAdapter mAdapter;        private File cache;             @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                 mListView = (ListView) findViewById(R.id.listView);                 //创建缓存目录，系统一运行就得创建缓存目录的，        cache = new File(Environment.getExternalStorageDirectory(), "cache");                 if(!cache.exists()){                cache.mkdirs();        }                 //获取数据，主UI线程是不能做耗时操作的，所以启动子线程来做        new Thread(){                public void run() {                        ContactService service = new ContactService();                        List<Contact> contacts = null;                                try {                                        contacts = service.getContactAll();                                } catch (Exception e) {                                        e.printStackTrace();                                }                                //子线程通过Message对象封装信息，并且用初始化好的，                                //Handler对象的sendMessage()方法把数据发送到主线程中，从而达到更新UI主线程的目的                        Message msg = new Message();                        msg.what = SUCCESS_GET_CONTACT;                        msg.obj = contacts;                        mHandler.sendMessage(msg);                };        }.start();    }         private Handler mHandler = new Handler(){                public void handleMessage(android.os.Message msg) {                        if(msg.what == SUCCESS_GET_CONTACT){                                List<Contact> contacts = (List<Contact>) msg.obj;                                mAdapter = new ImageAdapter(getApplicationContext(),contacts,cache);                                mListView.setAdapter(mAdapter);                        }                };        };         @Override    protected void onDestroy() {            super.onDestroy();            //清空缓存            File[] files = cache.listFiles();            for(File file :files){                    file.delete();            }            cache.delete();    }}

服务器xml文件

<?xml version="1.0" encoding="UTF-8"?><contacts>        <contact id="1">                <name>图标1</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/1.png" />        </contact>        <contact id="2">                <name>图标2</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/2.png" />        </contact>        <contact id="3">                <name>图标3</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/3.png" />        </contact>        <contact id="4">                <name>图标4</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/4.png" />        </contact>        <contact id="5">                <name>图标5</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/5.png" />        </contact>        <contact id="6">                <name>图标6</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/6.png" />        </contact>        <contact id="7">                <name>图标7</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/7.png" />        </contact>        <contact id="8">                <name>图标8</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/8.png" />        </contact>        <contact id="9">                <name>图标9</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/9.png" />        </contact>        <contact id="10">                <name>图标10</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/10.png" />        </contact>        <contact id="11">                <name>图标11</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/11.png" />        </contact>        <contact id="12">                <name>图标12</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/12.png" />        </contact>         <contact id="13">                <name>图标13</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/13.png" />        </contact>        <contact id="14">                <name>图标14</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/14.png" />        </contact>        <contact id="15">                <name>图标15</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/15.png" />        </contact>        <contact id="16">                <name>图标16</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/16.png" />        </contact>        <contact id="17">                <name>图标17</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/17.png" />        </contact>        <contact id="18">                <name>图标18</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/18.png" />        </contact>        <contact id="19">                <name>图标19</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/19.png" />        </contact>        <contact id="20">                <name>图标20</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/20.png" />        </contact>                 <contact id="21">                <name>图标21</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/1.png" />        </contact>        <contact id="22">                <name>图标22</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/2.png" />        </contact>        <contact id="23">                <name>图标23</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/3.png" />        </contact>        <contact id="24">                <name>图标24</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/4.png" />        </contact>        <contact id="25">                <name>图标25</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/5.png" />        </contact>        <contact id="26">                <name>图标26</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/6.png" />        </contact>        <contact id="27">                <name>图标27</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/7.png" />        </contact>        <contact id="28">                <name>图标28</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/8.png" />        </contact>        <contact id="29">                <name>图标29</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/9.png" />        </contact>        <contact id="30">                <name>图标30</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/10.png" />        </contact>        <contact id="31">                <name>图标31</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/11.png" />        </contact>        <contact id="32">                <name>图标32</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/12.png" />        </contact>         <contact id="33">                <name>图标33</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/13.png" />        </contact>        <contact id="34">                <name>图标34</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/14.png" />        </contact>        <contact id="35">                <name>图标35</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/15.png" />        </contact>        <contact id="36">                <name>图标36</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/16.png" />        </contact>        <contact id="37">                <name>图标37</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/17.png" />        </contact>        <contact id="38">                <name>图标38</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/18.png" />        </contact>        <contact id="39">                <name>图标39</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/19.png" />        </contact>        <contact id="40">                <name>图标40</name>                <image src="http://192.168.34.20:8080/AsyncTaskTest/image/20.png" />        </contact></contacts>

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