标签：缓存 disklrucache oom lrucache
上次讲了使用内存缓存LruCache去加载很多图片而不造成OOM，而这种缓存的特点是在应用程序运行时管理内存中的资源（图片）的存储和释放，如果LruCache中有一张图片被释放了，再次加载该图片时需要重新从网络上下载下来，这就显得废流量不说，而且费时，网络不好的状况下用户需要等待，而且在没有网络的情况下不会显示任何数据。
那么怎样才能解决这种情况呢？答案就是加入硬盘缓存DiskLruCache。
/**
* @param cacheDirName - 缓存的最终目录文件夹名称
* @return - 获取硬盘缓存的目录
*/
private File getDiskLruCacheDir(Context context, String cacheDirName) {
String cachePath;
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
|| !Environment.isExternalStorageRemovable()) {
cachePath = context.getExternalCacheDir().getPath();
} else {
cachePath = context.getCacheDir().getPath();
}
File file = new File(cachePath + "/" + cacheDirName);
if (!file.exists()) {
file.mkdirs();
}
return file;
}
public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize)需要传入四个参数，意思分别为：
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0); int versionID = info.versionCode;
DiskLruCache mBitmapDiskLruCache = null;
File file = getDiskLruCacheDir(this, "bitmap");
int versionID = getAppVersionNum(this);
try {
mBitmapDiskLruCache = DiskLruCache.open(file, versionID, 1, 10 * 1024 * 1024);
} catch (IOException e) {
e.printStackTrace();
}getDiskLruCacheDir(): private File getDiskLruCacheDir(Context context, String cacheDirName) {
String cachePath;
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
|| !Environment.isExternalStorageRemovable()) {
cachePath = context.getExternalCacheDir().getPath();
} else {
cachePath = context.getCacheDir().getPath();
}
File file = new File(cachePath + "/" + cacheDirName);
if (!file.exists()) {
file.mkdirs();
}
return file;
}getAppVersionNum():private int getAppVersionNum(Context context) {
try {
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
return info.versionCode;
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
}
return 1;
}好了，DiskLruCache对象就创建好了，接下来就是根据我们创建的DiskLruCache对象来对进行数据的一系列操作了。public Editor edit(String key)可以看到我们需要传入一个key值，这就是缓存文件的名称了，这个key值一般情况下我们会采用md5(url)的形式，就是把数据(图片等)对应的url进行md5进行编码加密后即可。
public class String2MD5Tools {
/**
* @param key
* @return
* 对key进行MD5加密并返回加密过的散列值
*/
public static String hashKeyForDisk(String key) {
String cacheKey;
try {
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(key.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
} catch (NoSuchAlgorithmException e) {
cacheKey = String.valueOf(key.hashCode());
}
return cacheKey;
}
private static String bytesToHexString(byte[] bytes) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < bytes.length; i++) {
String hex = Integer.toHexString(0xFF & bytes[i]);
if (hex.length() == 1) {
sb.append('0');
}
sb.append(hex);
}
return sb.toString();
}
}
然后通过调用hashKeyForDisk就可以对url进行编码了：String key = String2MD5Tools.hashKeyForDisk(url);好了，回到edit()方法上，该方法返回的是一个DiskLruCache.Editor类型的对象，Editor是DiskLruCache的一个成员内部类：
DiskLruCache.Editor editor = mBitmapDiskLruCache.edit(String2MD5Tools.hashKeyForDisk(url));
if (editor != null) {
OutputStream outputStream = editor.newOutputStream(0);//得到输出流，往里面写数据
bitmap = downloadBitmap(url, outputStream);//把刚刚下载的图片存入硬盘缓存中，对应的key值为md5(url)
if (bitmap != null) {
editor.commit();//提交表示写入缓存成功
}else{
editor.abort();//表示放弃此次写入
}
}
/**
* 从网络上下载图片,下载时候把下载的图片写入OutputStream中
* @param urlStr
* @return
*/
private Bitmap downloadBitmap(String urlStr, OutputStream outputStream) {
HttpURLConnection connection = null;
BufferedOutputStream bufferedOutputStream;
Bitmap bitmap = null;
try {
URL url = new URL(urlStr);
connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5000);
connection.setReadTimeout(5000);
connection.setDoInput(true);
connection.setDoOutput(true);
connection.connect();
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream mInputStream = connection.getInputStream();
bitmap = BitmapFactory.decodeStream(mInputStream);
bufferedOutputStream = new BufferedOutputStream(outputStream);
int len=-1;
byte[] by = new byte[1024];
while ((len = mInputStream.read(by)) != -1) {
bufferedOutputStream.write(by, 0, len);
}
bufferedOutputStream.flush();
bufferedOutputStream.close();
mInputStream.close();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
}
return bitmap;
}当然，上述写入数据到缓存的过程需要放到另外一个线程中去执行，原因肯定不用我多说，因为有请求网络的操作。public synchronized Snapshot get(String key)可知它需要传入一个key值，这里我想都知道怎么传入这个key值吧，就是我们通过md5(url)编码后的key值，该方法是根据我们传入的key值来查找对应了缓存文件名称，如果找到了key和缓存文件名一样那就返回一个Snapshot类型的对象，如果没找到就返回null。
DiskLruCache.Snapshot snapshot = mBitmapDiskLruCache.get(String2MD5Tools.hashKeyForDisk(url));
if (snapshot != null) {//如果硬盘缓存中存在该缓存文件
InputStream inputStream = snapshot.getInputStream(0);//获得该缓存文件的输入流
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);//把输入流解析成Bitmap
if (bitmap != null) {
mImageView.setImageBitmap(bitmap);
}else{
//硬盘缓存中不存在图片缓存则开启一个线程去下载图片
//do sthing
}
public synchronized boolean remove(String key)代码很简单，传入指定的key即可删除对应名称的缓存文件：
boolean flag = mBitmapDiskCache.remove(String2MD5Tools.hashKeyForDisk(url));
if(flag){
//删除成功
}else{
//删除失败
}
long totalCacheSize = mBitmapDiskLruCache.size();像很多应用都会在设置界面下显示该app的缓存大小，其实就是通过它得到的，然后我们可以手动清除它，清除全部的缓存数据是使用：
mBitmapDiskLruCache.delete();来清空缓存数据。
mBitmapDiskLruCache.flush();完成的，通常我们会在OnPause()方法中调用它，表示操作全部结束后进行同步记录。
mBitmapDiskLruCache.close();通常我们会在onDestroy()方法中调用它，那么完整的代码为：
@Override
protected void onPause() {
super.onPause();
try {
if (mBitmapDiskLruCache != null) {
mBitmapDiskLruCache.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
protected void onDestroy() {
super.onDestroy();
try {
if (mBitmapDiskLruCache != null) {
mBitmapDiskLruCache.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
public class MainActivity extends ActionBarActivity {
private ImageView mImageView;
private TextView mTextView;
private String url = "http://img.my.csdn.net/uploads/201507/21/1437459521_5133.jpg";
private DiskLruCache mBitmapDiskLruCache ;
private DiskLruCache mTextDiskLruCache;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mImageView = (ImageView) findViewById(R.id.imageView);
mTextView = (TextView) findViewById(R.id.textView);
initBitmapDiskLruCache();
initTextDiskLruCache();
loadBitmap(url, mBitmapDiskLruCache,mTextDiskLruCache);
}
//初始化硬盘缓存，得到缓存对象
public void initBitmapDiskLruCache() {
File file = getDiskLruCacheDir(this, "bitmap");
int versionID = getAppVersionNum(this);
try {
mBitmapDiskLruCache = DiskLruCache.open(file, versionID, 1, 10 * 1024 * 1024);
} catch (IOException e) {
e.printStackTrace();
}
}
public void initTextDiskLruCache() {
File file = getDiskLruCacheDir(this, "text");
int versionID = getAppVersionNum(this);
try {
mTextDiskLruCache = DiskLruCache.open(file, versionID, 1, 10 * 1024 * 1024);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 加载图片和文本数据，先判断硬盘缓存中有木有，有则从硬盘缓存中取出设置，没有则开启线程下载数据
* @param url
* @param mBitmapDiskLruCache
* @param mTextDiskLruCache
*/
public void loadBitmap(String url, DiskLruCache mBitmapDiskLruCache,DiskLruCache mTextDiskLruCache) {
try {
//从硬盘缓存中加载图片
DiskLruCache.Snapshot snapshot = mBitmapDiskLruCache.get(String2MD5Tools.hashKeyForDisk(url));
if (snapshot != null) {//如果硬盘缓存中存在该缓存文件
InputStream inputStream = snapshot.getInputStream(0);
Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
if (bitmap != null) {
mImageView.setImageBitmap(bitmap);
}
}else{
//硬盘缓存中不存在图片缓存则开启一个线程去下载图片
DownloadTask task = new DownloadTask(mImageView, mTextView,mBitmapDiskLruCache,mTextDiskLruCache);
task.execute(url);
}
DiskLruCache.Snapshot snapshot1 = mTextDiskLruCache.get(String2MD5Tools.hashKeyForDisk(url));
if(snapshot1!=null){
InputStream inputStream = snapshot1.getInputStream(0);
if(inputStream!=null){
int len=-1;
byte[] by = new byte[1024];
StringBuilder builder = new StringBuilder();
while ((len=inputStream.read(by))!=-1){
builder.append(new String(by,0,len));
}
mTextView.setText(builder.toString());
}
}else{
//硬盘缓存中不存在文本缓存则开启一个线程去下载
DownloadTask task = new DownloadTask(mImageView, mTextView,mBitmapDiskLruCache,mTextDiskLruCache);
task.execute(url);
}
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* @param context
* @return - 得到应用的版本号
*/
private int getAppVersionNum(Context context) {
try {
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
return info.versionCode;
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
}
return 1;
}
/**
* @param cacheDirName - 缓存的最终目录文件夹名称
* @return - 获取硬盘缓存的目录
*/
private File getDiskLruCacheDir(Context context, String cacheDirName) {
String cachePath;
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
|| !Environment.isExternalStorageRemovable()) {
cachePath = context.getExternalCacheDir().getPath();
} else {
cachePath = context.getCacheDir().getPath();
}
File file = new File(cachePath + "/" + cacheDirName);
if (!file.exists()) {
file.mkdirs();
}
return file;
}
@Override
protected void onPause() {
super.onPause();
try {
if (mBitmapDiskLruCache != null) {
mBitmapDiskLruCache.flush();
}
if(mTextDiskLruCache!=null){
mTextDiskLruCache.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
protected void onDestroy() {
super.onDestroy();
try {
if (mBitmapDiskLruCache != null) {
mBitmapDiskLruCache.close();
}
if(mTextDiskLruCache!=null){
mTextDiskLruCache.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}异步下载类：public class DownloadTask extends AsyncTask<String, Void, Bitmap> {
private ImageView imageView;
private TextView mTextView;
private String url;
private DiskLruCache mBitmapDiskLruCache;
private DiskLruCache mTextDiskLruCache;
public DownloadTask(ImageView imageView,TextView mTextView, DiskLruCache mBitmapDiskLruCache,DiskLruCache mTextDiskLruCache) {
this.imageView = imageView;
this.mTextView = mTextView;
this.mBitmapDiskLruCache = mBitmapDiskLruCache;
this.mTextDiskLruCache = mTextDiskLruCache;
}
@Override
protected Bitmap doInBackground(String... params) {
url = params[0];
Bitmap bitmap=null;
boolean flag = false;
try {
//将下载的图片写入硬盘缓存中，bitmap目录下
DiskLruCache.Editor editor = mBitmapDiskLruCache.edit(String2MD5Tools.hashKeyForDisk(url));
if (editor != null) {
OutputStream outputStream = editor.newOutputStream(0);
flag = downloadBitmap(url,outputStream);
if(flag){
editor.commit();//提交表示写入缓存成功
}else{
editor.abort();//表示放弃此次写入
}
}
//从硬盘缓存中获取图片
DiskLruCache.Snapshot snapshot = mBitmapDiskLruCache.get(String2MD5Tools.hashKeyForDisk(url));
if(snapshot!=null){
InputStream inputStream = snapshot.getInputStream(0);
if(inputStream!=null){
bitmap = BitmapFactory.decodeStream(inputStream);//
}
}
//将图片的文本数据写入硬盘缓存，text目录下
DiskLruCache.Editor editor1 = mTextDiskLruCache.edit(String2MD5Tools.hashKeyForDisk(url));
if(editor1!=null){
OutputStream outputStream = editor1.newOutputStream(0);
if(bitmap!=null){
outputStream.write(("height=" + bitmap.getHeight() + ",width=" + bitmap.getWidth()).toString().getBytes());
editor1.commit();
}else{
editor1.abort();
}
}
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
if(imageView!=null&&bitmap!=null){
imageView.setImageBitmap(bitmap);
}
if(mTextView!=null&&bitmap!=null){
mTextView.setText(("height="+bitmap.getHeight()+",width="+bitmap.getWidth()).toString());
}
}
/**
* 从网络上下载图片
* @param urlStr
* @return
*/
private boolean downloadBitmap(String urlStr,OutputStream outputStream) {
HttpURLConnection connection = null;
Bitmap bitmap = null;
BufferedOutputStream bos;
try {
URL url = new URL(urlStr);
connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(5000);
connection.setReadTimeout(5000);
connection.setDoInput(true);
connection.setDoOutput(true);
connection.connect();
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream mInputStream = connection.getInputStream();
bos = new BufferedOutputStream(outputStream);
int len=-1;
byte[] by = new byte[1024];
while((len=mInputStream.read(by))!=-1){
bos.write(by,0,len);
bos.flush();
}
mInputStream.close();
return true;
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
}
return false;
}
}版权声明：本文为博主原创文章，未经博主允许不得转载。转载注明出处：http://blog.csdn.net/u010687392
标签：缓存 disklrucache oom lrucache
原文地址：http://blog.csdn.net/u010687392/article/details/47019505
