图片的LruCache缓存和DiskLruCache缓存

本文主要是介绍图片的LruCache缓存和DiskLruCache缓存，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

LruCache中内置LRU算法，LRU是Least Recently Used的缩写，即最近最少使用页面置换算法，这个算法会把最少使用的部分删除，保留使用次数最多的部分。

DiskLruCache采用本地文件缓存，把一部分图片缓存在本地，等再次用到直接从本地加载，无需从网络上下载图片；

很好的结合使用两种缓存，可以加快图片的加载，减少网络请求次数，节省手机流量；

加载图片先从LruCache中查找，没有，再从DiskLruCache中找，没有，最后再异步加载请求网络图片；

ImageUtils.java

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Environment;
import android.util.LruCache;
import android.widget.ImageView;
import android.widget.Toast;import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;/*** Created by Administrator on 2016/5/15.*/
public class ImageUtils {public int cacheSize;//缓存的大小public int maxSize;//最大缓存public final static int MAXCOUNT=20;//文件缓存的最大数量public LruCache<String,Bitmap> lruCache;//初始化LruCachepublic int currentCount=0;//当前缓存的数量public ImageUtils() {//获得运行时的最大缓存maxSize= (int) Runtime.getRuntime().maxMemory();cacheSize=maxSize/8;//LruCache的初始化lruCache=new LruCache<String, Bitmap>(cacheSize){@Overrideprotected int sizeOf(String key, Bitmap value) {return value.getByteCount();}};}public void LoadImage(Context context,String url,ImageView imageView) {if (isNetWorkConnected(context)) {//从LruCache中找图片if (lruCache.get(url) != null) {Bitmap bitmap = lruCache.get(url);imageView.setImageBitmap(bitmap);} else {//从缓存在本地的文件中找图片Bitmap bitmap = readFileToBitmap(context, url);if (bitmap != null) {//找到后加载到LruCachelruCache.put(url, bitmap);deleteFileOnDisk(context, url);imageView.setImageBitmap(bitmap);} else {//从网络中获取图片new ImageAsyncTask(context, url, imageView).execute(url);}}} else {Toast.makeText(context, "当前网络不可用", Toast.LENGTH_LONG).show();if (lruCache.get(url) != null) {imageView.setImageBitmap(lruCache.get(url));} else {Bitmap bitmap = readFileToBitmap(context, url);if (bitmap != null) {//deleteFileOnDisk(context, url);lruCache.put(url, bitmap);imageView.setImageBitmap(bitmap);} else {return;}}}}/*** 判断网络是否可用*/public boolean isNetWorkConnected(Context context){ConnectivityManager cm= (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);NetworkInfo netWorkInfo=cm.getActiveNetworkInfo();return netWorkInfo!=null&&netWorkInfo.isConnectedOrConnecting();}/*** 从文件夹中读取图片* @return*/public Bitmap readFileToBitmap(Context context, String url){File file=new File(getDiskCacheDir(context,url));Bitmap bitmap=null;try {FileInputStream fileInputStream=new FileInputStream(file);bitmap=BitmapFactory.decodeStream(fileInputStream);} catch (FileNotFoundException e) {bitmap=null;}return bitmap;}/*** 从本地文件中删除* @param context* @param url*/public void deleteFileOnDisk(Context context,String url){File file=new File(getDiskCacheDir(context,url));file.delete();}/***保存图片到文件中*/public void addToDiskCache(Context context,String url,Bitmap bitmap){File file=new File(getDiskCacheDir(context,url));FileOutputStream fileOP=null;try {file.createNewFile();fileOP=new FileOutputStream(file);bitmap.compress(Bitmap.CompressFormat.JPEG,64,fileOP);fileOP.flush();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {try {if(fileOP!=null) {fileOP.close();}} catch (IOException e) {e.printStackTrace();}}}/*** 根据有无内存卡，获取保存文件的路径* @param context* @param fileName* @return*/public String getDir(Context context, String fileName){String diskCacheDir;if(Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())&&!Environment.isExternalStorageRemovable()){diskCacheDir=context.getExternalCacheDir().getPath();}else {diskCacheDir=context.getCacheDir().getPath();}diskCacheDir=diskCacheDir+ File.separator+fileName;return diskCacheDir;}/*** 获取本地缓存路径* @param context* @param url* @return*/public String getDiskCacheDir(Context context, String url){String fileDir=hashkeyForDisk(url);fileDir= getDir(context,fileDir);return fileDir;}/*** 获取url的hashkey* @param url* @return*/public String hashkeyForDisk(String url){String fileName;try {MessageDigest messageDigest=MessageDigest.getInstance("MD5");messageDigest.update(url.getBytes());fileName=bytesToHexString(messageDigest.digest());} catch (NoSuchAlgorithmException e) {fileName=String.valueOf(url.hashCode());}return fileName;
}/*** 和16进制进行&运算* @param bytes* @return*/public String bytesToHexString(byte bytes[]){StringBuilder stringBuilder =new StringBuilder();for(int i=0;i<bytes.length;i++){String hex=Integer.toHexString(0xFF&bytes[i]);if(hex.length()==1){stringBuilder.append('0');}stringBuilder.append(hex);}return stringBuilder.toString();}/*** 异步加载图片*/class ImageAsyncTask extends AsyncTask<String,Void,Bitmap>{private ImageView imageView;private String url;private Context context;public ImageAsyncTask(Context context,String url,ImageView imageView) {this.imageView = imageView;this.context=context;this.url = url;}@Overrideprotected Bitmap doInBackground(String... params) {InputStream inputStream=HttpUtils.getInputStream(params[0]);return BitmapFactory.decodeStream(inputStream);}@Overrideprotected void onPostExecute(Bitmap bitmap) {super.onPostExecute(bitmap);if(bitmap!=null&&imageView!=null) {//根据Tag设置图片，防止图片错乱if (imageView.getTag()==url) {imageView.setImageBitmap(bitmap);//把加载的图片放入LruCache中lruCache.put(url, bitmap);if(currentCount<MAXCOUNT) {//放入硬盘缓存中addToDiskCache(context, url, bitmap);currentCount++;}}}}}
}

HttpUtils.java

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;/*** Created by Administrator on 2016/5/15.*/
public class HttpUtils {public static InputStream getInputStream(String url){InputStream inputStream=null;try {URLConnection urlConnection= new URL(url).openConnection();inputStream =urlConnection.getInputStream();} catch (IOException e) {e.printStackTrace();}return inputStream;}}

如有错误，欢迎指出

参考博客地址：http://blog.csdn.net/guolin_blog/article/details/28863651

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