三级缓存的原理代码实现
1.在activity中书写imageview的控件
2.调用工具类BitmapUtils；
在工具类中具体实现三级缓存的原理展示代码如下：
Context context;
//图片本地缓存路径
private final static String SDCARD_CACHE = Environment.getExternalStorageDirectory() + "/imagecache";
//图片存放文件夹
File fileDir = new File(SDCARD_CACHE);
private Map
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what) {
case 0:
ImageViewToBitmap imageViewToBitmap = (ImageViewToBitmap) msg.obj;
imageViewToBitmap.iv.setImageBitmap(imageViewToBitmap.bitmap);
break;
}
}
};
//构造方法
public BitmapUtils(Context context) {
this.context = context;
if (!fileDir.exists()) {
fileDir.mkdirs();
}
}
//加载图片的方法
public void display(ImageView iv, String url) {
//内存缓存
Bitmap bitmap = loadMemory(url);
if (bitmap != null) {
iv.setImageBitmap(bitmap);
} else {
//sdcard缓存
bitmap = loadSD(url);
if (bitmap != null) {
iv.setImageBitmap(bitmap);
} else {
//网络缓存
loadInternetImage(iv, url);
}
}
}
private Bitmap loadMemory(String url) {
SoftReference
if (value != null) {
Bitmap bitmap = value.get();
return bitmap;
}
return null;
}
//获取本地图片
private Bitmap loadSD(String url) {
String name = getFileName(url);
File file = new File(fileDir, name);
if (file.exists()) {
//BitmapFactory选项
BitmapFactory.Options options = new BitmapFactory.Options();
//加载图片宽高
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(name, options);
//获取图片和手机屏幕宽高
int outWidth = options.outWidth;
int outHeight = options.outHeight;
DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
int widthPixels = displayMetrics.widthPixels;
int heightPixels = displayMetrics.heightPixels;
//图片跟手机屏幕进行比对
int scale = 0;
int scaleX = outWidth / widthPixels;
int scaleY = outHeight / heightPixels;
scale = scaleX > scaleY ? scaleX : scaleY;
if (scale == 0) {
scale = 1;
}
options.inJustDecodeBounds = false;
options.inSampleSize = scale;
Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath(), options);
//内存缓存
SoftReference
map.put(name, value);
return bitmap;
}
return null;
}
//获取网络图片
private void loadInternetImage(ImageView iv, String url) {
//开子线程做耗时操作
new Thread(new DownloadImage(iv, url)).start();
}
private class DownloadImage implements Runnable {
ImageView iv;
String url;
private InputStream inputStream;
private FileOutputStream fos;
public DownloadImage(ImageView iv, String url) {
this.iv = iv;
this.url = url;
}
@Override
public void run() {
try {
HttpClient clent = new DefaultHttpClient();
HttpGet get = new HttpGet(url);
HttpResponse execute = clent.execute(get);
if (execute.getStatusLine().getStatusCode() == 200) {
inputStream = execute.getEntity().getContent();
String name = getFileName(url);
File file = new File(fileDir, name);
fos = new FileOutputStream(file);
byte[] buffer = new byte[1024];
int len = 0;
while ((len = inputStream.read(buffer)) != -1) {
fos.write(buffer, 0, len);
}
//sdcard缓存
Bitmap bitmap = loadSD(name);
//ImageView转换成Bitmap转换成Bitmap
ImageViewToBitmap ivtb = new ImageViewToBitmap(iv, bitmap);
Message message = Message.obtain(handler, 0, ivtb);
message.sendToTarget();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
fos.close();
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
//获取图片的名称
private String getFileName(String url) {
return Md5Utils.encode(url) + ".jpg";
}
//ImageView转换成Bitmap转换成Bitmap
private class ImageViewToBitmap {
ImageView iv;
Bitmap bitmap;
public ImageViewToBitmap(ImageView iv, Bitmap bitmap) {
this.iv = iv;
this.bitmap = bitmap;
}
}
}
4，在工具类中的缓存中需要使用MD5，所以需要在谢一个工具类
public class Md5Utils {
public static String encode(String password){
try {
MessageDigest digest = MessageDigest.getInstance("MD5");
byte[] result = digest.digest(password.getBytes());
StringBuffer sb = new StringBuffer();
for(byte b : result){
int number = (int)(b & 0xff) ;
String str = Integer.toHexString(number);
if(str.length()==1){
sb.append("0");
}
sb.append(str);
}
return sb.toString();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
//can't reach
return "";
}
}
}
5，最后我们在activity中调用方法就能用到我们刚刚封装的工具类
private String url = "http://d.hiphotos.baidu.com/zhidao/pic/item/72f082025aafa40fe871b36bad64034f79f019d4.jpg";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//找控件
ImageView iv = (ImageView) findViewById(R.id.iv);
//实例化图片加载框架
BitmapUtils bitmapUtils = new BitmapUtils(this);
bitmapUtils.display(iv, url);
}
以上就是三级缓存的原理实现