一、概述
网络图片的加载在Android的开发中是一个必不可少的功能，今天我们就来聊聊网络图片加载三级缓存策略。
所谓的三级缓存策略是指通过网络、本地、内存三级来缓存图片，减少不必要的网络交互，避免浪费流量。
内存缓存, 优先加载, 速度最快本地缓存, 次优先加载, 速度快网络缓存, 不优先加载, 速度慢, 浪费流量
二、核心代码
网络图片加载工具类ImageLoader.java
package com.czhappy.helloimageloader;import android.graphics.Bitmap;import android.widget.ImageView;import com.czhappy.helloimageloader.core.LocalCacheUtils;import com.czhappy.helloimageloader.core.MemoryCacheUtils;import com.czhappy.CacheUtils;import com.czhappy.helloimageloader.utils.LogUtil;import com.czhappy.helloimageloader.utils.Utils;/*** Description:网络图片加载工具类* User: chenzheng* Date: /2/11 0011* Time: 11:21*/public class ImageLoader {private static ImageLoader mInstance = null;private NetCacheUtils mNetCacheUtils;private LocalCacheUtils mLocalCacheUtils;private MemoryCacheUtils mMemoryCacheUtils;public static ImageLoader getInstance(){if(mInstance==null){synchronized (ImageLoader.class){if(mInstance==null){mInstance = new ImageLoader();}}}return mInstance;}private ImageLoader(){mMemoryCacheUtils=new MemoryCacheUtils();mLocalCacheUtils=new LocalCacheUtils();mNetCacheUtils=new NetCacheUtils(mLocalCacheUtils,mMemoryCacheUtils);}/*** 加载网络图片* @param mImageView* @param url*/public void loadImageView(ImageView mImageView, String url) {mImageView.setImageResource(R.drawable.empty_photo);if(Utils.isEmpty(url)){return;}Bitmap bitmap;//内存缓存LogUtil.i("尝试从内存中获取图片...");bitmap=mMemoryCacheUtils.getBitmapFromMemory(url);if (bitmap!=null){mImageView.setImageBitmap(bitmap);return;}//本地缓存LogUtil.i("尝试从本地获取图片...");bitmap = mLocalCacheUtils.getBitmapFromLocal(url);if(bitmap !=null){mImageView.setImageBitmap(bitmap);//从本地获取图片后,保存至内存中mMemoryCacheUtils.setBitmapToMemory(url,bitmap);return;}//网络缓存LogUtil.i("尝试从网络获取图片...");mNetCacheUtils.getBitmapFromNet(mImageView,url);}}
内存缓存MemoryCacheUtils.java
package com.czhappy.helloimageloader.core;import android.graphics.Bitmap;import android.util.LruCache;/*** Description: 内存缓存* User: chenzheng* Date: /2/11 0011* Time: 11:15*/public class MemoryCacheUtils {private LruCache<String,Bitmap> mMemoryCache;public MemoryCacheUtils(){long maxMemory = Runtime.getRuntime().maxMemory()/8;//得到手机最大允许内存的1/8,即超过指定内存,则开始回收//需要传入允许的内存最大值,虚拟机默认内存16M,真机不一定相同mMemoryCache=new LruCache<String,Bitmap>((int) maxMemory){//在每次存入缓存的时候调用,用于计算每个条目的大小@Overrideprotected int sizeOf(String key, Bitmap value) {int byteCount = value.getByteCount();return byteCount;}};}/*** 从内存中读图片* @param url*/public Bitmap getBitmapFromMemory(String url) {Bitmap bitmap = mMemoryCache.get(url);return bitmap;}/*** 往内存中写图片* @param url* @param bitmap*/public void setBitmapToMemory(String url, Bitmap bitmap) {mMemoryCache.put(url,bitmap);}}
本地缓存LocalCacheUtils.java
package com.czhappy.helloimageloader.core;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.Environment;import com.czhappy.helloimageloader.utils.MD5Util;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;/*** Description: 本地缓存* User: chenzheng* Date: /2/11 0011* Time: 11:15*/public class LocalCacheUtils {private static final String CACHE_PATH= Environment.getExternalStorageDirectory().getAbsolutePath()+"/HelloImageLoader";/*** 从本地读取图片* @param url*/public Bitmap getBitmapFromLocal(String url){String fileName = null;//把图片的url当做文件名,并进行MD5加密try {fileName = MD5Util.GetMD5Code(url);File file=new File(CACHE_PATH,fileName);if(file.exists()){Bitmap bitmap = BitmapFactory.decodeStream(new FileInputStream(file));return bitmap;}} catch (Exception e) {e.printStackTrace();}return null;}/*** 从网络获取图片后,保存至本地缓存* @param url* @param bitmap*/public void setBitmapToLocal(String url,Bitmap bitmap){try {String fileName = MD5Util.GetMD5Code(url);//把图片的url当做文件名,并进行MD5加密File file=new File(CACHE_PATH,fileName);//通过得到文件的父文件,判断父文件是否存在File parentFile = file.getParentFile();if (!parentFile.exists()){parentFile.mkdirs();}//把图片保存至本地press(pressFormat.JPEG,100,new FileOutputStream(file));} catch (Exception e) {e.printStackTrace();}}}
网络缓存NetCacheUtils.java
package com.czhappy.helloimageloader.core;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.widget.ImageView;import java.io.IOException;import .HttpURLConnection;import .URL;/*** Description: 网络缓存* User: chenzheng* Date: /2/11 0011* Time: 11:15*/public class NetCacheUtils {private LocalCacheUtils mLocalCacheUtils;private MemoryCacheUtils mMemoryCacheUtils;public NetCacheUtils(LocalCacheUtils localCacheUtils, MemoryCacheUtils memoryCacheUtils) {mLocalCacheUtils = localCacheUtils;mMemoryCacheUtils = memoryCacheUtils;}/*** 从网络下载图片* @param mImageView 显示图片的imageview* @param url 下载图片的网络地址*/public void getBitmapFromNet(ImageView mImageView, String url) {new BitmapTask().execute(mImageView, url);//启动AsyncTask}/*** AsyncTask就是对handler和线程池的封装* 第一个泛型:参数类型* 第二个泛型:更新进度的泛型* 第三个泛型:onPostExecute的返回结果*/class BitmapTask extends AsyncTask<Object, Void, Bitmap> {private ImageView mImageView;private String url;/*** 后台耗时操作,存在于子线程中* @param params* @return*/@Overrideprotected Bitmap doInBackground(Object[] params) {mImageView = (ImageView) params[0];url = (String) params[1];return downLoadBitmap(url);}/*** 更新进度,在主线程中* @param values*/@Overrideprotected void onProgressUpdate(Void[] values) {super.onProgressUpdate(values);}/*** 耗时方法结束后执行该方法,主线程中* @param result*/@Overrideprotected void onPostExecute(Bitmap result) {if (result != null) {mImageView.setImageBitmap(result);//从网络获取图片后,保存至本地缓存mLocalCacheUtils.setBitmapToLocal(url, result);//保存至内存中mMemoryCacheUtils.setBitmapToMemory(url, result);}}}/*** 网络下载图片* @param url* @return*/private Bitmap downLoadBitmap(String url) {HttpURLConnection conn = null;try {conn = (HttpURLConnection) new URL(url).openConnection();conn.setConnectTimeout(5000);conn.setReadTimeout(5000);conn.setRequestMethod("GET");int responseCode = conn.getResponseCode();if (responseCode == 200) {//图片压缩BitmapFactory.Options options = new BitmapFactory.Options();options.inSampleSize=2;//宽高压缩为原来的1/2options.inPreferredConfig=Bitmap.Config.ARGB_4444;Bitmap bitmap = BitmapFactory.decodeStream(conn.getInputStream(),null,options);return bitmap;}} catch (IOException e) {e.printStackTrace();} finally {conn.disconnect();}return null;}}
测试类
package com.czhappy.helloimageloaderdemo;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.widget.ImageView;import com.czhappy.helloimageloader.ImageLoader;public class MainActivity extends AppCompatActivity {private ImageView my_image;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);my_image = (ImageView) findViewById(R.id.my_image);}public void beginLoad(View view){String url = "/images/1112/tooopen_sy_185726882764.jpg";ImageLoader.getInstance().loadImageView(my_image, url);}}
三、实现效果图
