Android利用DiskLruCache和LruCache实现简单的照片墙

柔光的暖阳◎ 2021-11-08 22:36 416阅读 0赞

现在很多App的某些功能会把图片以及内容缓存在本地，即使是没有网络的情况下也还是可以加载出之前浏览过的内容来，这些功能就是使用了DiskLruCache技术；

LruCache负责管理内存中图片的存储与释放，如果图片从内存中被移除的话，那么又需要从网络上重新加载一次图片，这显然非常耗时，所以Google又提供了一套硬盘缓存的解决方案：DiskLruCache；  
DiskLruCache并没有限制数据的缓存位置，可以自由地进行设定，不过一般来说会存储在SD卡中， 当SD卡存在或者SD卡不可被移除的时候，就调用getExternalCacheDir()方法来获取缓存路径，否则就调用getCacheDir()方法来获取缓存路径。 前者获取到的就是 /sdcard/Android/data//cache 这个路径 而后者获取到的是 data/data/<application - package>/cache这个路径,接下来就用一个简单的照片墙demo来阐述DiskLruCache以及LruCache缓存技术吧；

先附上我的项目结构  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyODg5NDc2_size_16_color_FFFFFF_t_70]

DiskLruCache这个类并没有在android api中，所以需要从网上下载下来，然后加在项目中就可以了，这里我就附上链接了  
[https://download.csdn.net/download/qq\_42889476/11485240][https_download.csdn.net_download_qq_42889476_11485240]

因为图片的话是需要机密处理的，所以我们需要一个工具类----MD5转换工具类

package com.example.disklrucache_demo;
    
    import java.math.BigInteger;
    import java.security.MessageDigest;
    import java.security.NoSuchAlgorithmException;
    
    public class MD5Utils {
        //使用MD5加密算法
        public static String md5(String plainText){
            byte[] secretBytes = null;
    
            try {
                secretBytes = MessageDigest.getInstance("md5").digest(plainText.getBytes());
            } catch (NoSuchAlgorithmException e) {
                throw new RuntimeException("没有md5这个算法！");
            }
            //16进制
            String md5Code = new BigInteger(1,secretBytes).toString(16);
            // 如果生成数字未满32位，需要前面补0
            for (int i = 0; i < 32 - md5Code.length(); i++) {
                md5Code = "0" + md5Code;
            }
            return md5Code;
        }
    }

然后是数据集合

package com.example.disklrucache_demo;
    
    public class Images {
        public final static String[] imageThumbUrls = new String[]{
                "http://image.biaobaiju.com/uploads/20180211/01/1518283483-ZSaWgidtGK.jpg",
                "http://img.51ztzj.com/upload/image/20131024/dn201310242017_670x419.jpg",
                "http://image.biaobaiju.com/uploads/20180803/20/1533300593-nYwpoTMUEs.jpg",
                "http://img.juimg.com/tuku/yulantu/130316/267856-1303160U31010.jpg",
                "http://pic1.win4000.com/wallpaper/2017-10-18/59e7096016774.jpg",
                "http://gss0.baidu.com/-Po3dSag_xI4khGko9WTAnF6hhy/zhidao/pic/item/b64543a98226cffcad22c094ba014a90f603ea88.jpg",
                "http://img.pconline.com.cn/images/photoblog/1/0/1/5/10159318/200911/4/1257320021267_mthumb.jpg",
                "http://img3.duitang.com/uploads/item/201605/18/20160518232450_zxyFi.thumb.700_0.jpeg",
                "http://img.tukexw.com/img/252557a08a4ae4d1.jpg",
                "http://img4q.duitang.com/uploads/blog/201409/18/20140918211053_zaFRk.thumb.700_0.jpeg",
                "http://www.zhutizhijia.net/uploads/120323/24-120323155524102.jpg",
                "http://image.biaobaiju.com/uploads/20180706/04/1530821556-qYtMwiolae.jpg",
                "http://b-ssl.duitang.com/uploads/item/201302/17/20130217212232_xAK5C.jpeg",
                "http://b-ssl.duitang.com/uploads/item/201201/23/20120123195204_A8CRN.thumb.700_0.jpg",
                "http://image.yy.com/yywebalbumbs2bucket/28e43cdd19324941b73fe57c09046ddd_1487870799169.jpeg",
                "http://img5.duitang.com/uploads/blog/201508/10/20150810145410_5xEQJ.thumb.700_0.jpeg",
                "http://photocdn.sohu.com/20120704/Img347284777.jpg",
                "http://img4q.duitang.com/uploads/item/201411/03/20141103115630_HMhnU.jpeg",
                "http://img1.doubanio.com/pview/event_poster/raw/public/6eec72f07eb8c98.jpg",
                "http://img4q.duitang.com/uploads/item/201306/23/20130623230957_fmVV4.thumb.700_0.jpeg",
                "http://img2.ph.126.net/RJc77dzeQTv8z2CHGmzzgQ==/1828179973736115230.jpg",
                "http://s10.sinaimg.cn/middle/950ebfd0nb5be42e39a09&690",
                "http://g.hiphotos.baidu.com/zhidao/pic/item/ae51f3deb48f8c54fa5fd5673a292df5e1fe7fed.jpg",
                "http://img21.mtime.cn/mg/2010/09/14/162329.60324301.jpg",
                "http://i1.szhomeimg.com/n/2013/04/10/0410171600540.JPG",
                "http://b-ssl.duitang.com/uploads/item/201609/18/20160918141907_WBG2A.jpeg",
                "http://k.zol-img.com.cn/sjbbs/6319/a6318625_s.jpg",
                "http://b-ssl.duitang.com/uploads/item/201205/16/20120516125715_AfAiz.jpeg",
                "http://b-ssl.duitang.com/uploads/item/201206/15/20120615095518_UB3CS.jpeg",
                "http://i1.sinaimg.cn/edu/2012/0413/U7516P42DT20120413140544.jpg",
                "http://www.cnr.cn/newscenter/gjxw/list/201305/W020130516373227379082.jpg",
                "http://b-ssl.duitang.com/uploads/item/201204/12/20120412130056_kKxcd.jpeg",
                "http://img.boqiicdn.com/Data/BK/A/1301/23/img84111358931890_y.jpg",
                "http://img3.100bt.com/upload/ttq/20130323/1364004564120.png",
                "http://img01.tooopen.com/Downs/images/2011/7/19/sy_2011071921084512107.jpg",
                "http://img2.shangxueba.com/img/lady_Img/20140808/17/E7EACCFD9928B5B0064022F8E0E7DB36.jpg"
        };
    }

注：（如果程序跑起来了是默认的图片的话，建议自己去网上找一点图片的链接，然后再跑一遍就OK了）  
activity\_main.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">
    
        <GridView
            android:id="@+id/grid_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:numColumns="3"
            android:verticalSpacing="10dp"
            android:horizontalSpacing="10dp"
            android:columnWidth="90dp"
            android:stretchMode="columnWidth"
            android:gravity="center">
    
        </GridView>
    
    </RelativeLayout>

item\_activity.xml

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
    
    
        <ImageView
            android:id="@+id/img_photo"
            android:layout_width="120dp"
            android:layout_height="120dp" />
    
    </LinearLayout>

网格布局有了，子item也有了，接下来就需要一个适配器了  
流程：继承ArrayAdatper，在构造函数传入必要参数后，然后在getView方法中来设置图片源，首先先设置成一张默认的图片，然后根据图片的URL去缓存中找是否有相关联的资源，如果没找到在磁盘缓存中找，如果还是没找到再去网络上下载，然后保存在磁盘缓存里，下载资源的话是一个耗时的操作，所以开启了一个内部类Async异步类去完成，把所有的耗时操作都安排在doInBackground里执行，然后下载好了会缓存在内存和磁盘中  
这个适配器的其他功能我都用代码注释好了，就不一一讲解了

package com.example.disklrucache_demo;
    
    import android.content.Context;
    import android.content.pm.PackageInfo;
    import android.content.pm.PackageManager;
    import android.graphics.Bitmap;
    
    import android.graphics.BitmapFactory;
    import android.os.AsyncTask;
    import android.os.Environment;
    import android.util.Log;
    import android.util.LruCache;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.ArrayAdapter;
    import android.widget.GridView;
    import android.widget.ImageView;
    
    import java.io.BufferedInputStream;
    import java.io.BufferedOutputStream;
    import java.io.File;
    import java.io.IOException;
    import java.io.OutputStream;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.util.HashSet;
    import java.util.Set;
    
    import static com.example.disklrucache_demo.MainActivity.TAG;
    
    
    public class ImageAdapter extends ArrayAdapter {
    
        //声明LruCache缓存对象
        private LruCache<String, Bitmap> lruCache;
        // 声明DiskLruCache硬盘缓存对象
        private DiskLruCache diskLruCache;
        //任务列表
        private Set<LoadImageAsync> tasks;
        //声明GridView对象
        private GridView gridView;
    
        public ImageAdapter(Context context, int textViewResourceId,String[] objects,GridView gridView) {
            super(context, textViewResourceId,objects);
            this.gridView = gridView;
            tasks = new HashSet<LoadImageAsync>();
            //初始化内存缓存LruCache,获取应用最大可占内存
            int MaxMemory = (int) Runtime.getRuntime().maxMemory();
            //设置最大内存的八分之一作为图片资源的缓存大小
            int LruMemory = MaxMemory / 8;
            lruCache = new LruCache<String, Bitmap>(LruMemory){
                @Override
                protected int sizeOf(String key, Bitmap value) {
                    //返回Bitmap对象所占大小，单位：kb
                    return value.getByteCount();
                }
            };
    
            //初始化硬盘缓存DiskLruCache，获取硬盘的缓存路径，参数2为所在缓存路径的文件夹的名称
            File directory = getDiskCacheDir(getContext(),"bitmap");
            if (!directory.exists()){
                //若文件不存在，则创建新的文件夹
                directory.mkdirs();
            }
            //获取App版本号
            int appVersion = getAppVersion(getContext());
            //缓存1：缓存文件路径，参数2：系统版本号，参数3：一个缓存路径对几个文件，缓存4：缓存的空间大小
            try {
                diskLruCache = DiskLruCache.open(directory,appVersion,1,1024*1024*10);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        /**
         * @param context
         * @param uniqueName
         * @return
         *         当SD卡存在或者SD卡不可被移除的时候，就调用getExternalCacheDir()方法来获取缓存路径，否则就调用getCacheDir
         *         ()方法来获取缓存路径。 前者获取到的就是 /sdcard/Android/data/<application-
         *         package>/cache 这个路径 而后者获取到的是 data/data/application - package>/cache
         *         这个路径。
         */
    
        public File getDiskCacheDir(Context context,String uniqueName){
            String cachePath;
            if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !Environment.isExternalStorageRemovable()){
                cachePath = context.getExternalCacheDir().getPath();
            }else {
                cachePath = context.getCacheDir().getPath();
            }
            return new File(cachePath + File.separator + uniqueName);
        }
    
        /**
         * @param context
         * @return 获取系统版本号
         */
        public int getAppVersion(Context context){
            try {
                PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(),0);
                return info.versionCode;
            } catch (PackageManager.NameNotFoundException e) {
                e.printStackTrace();
            }
            return 1;
        }
    
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            //获取图片资源URL地址
            String path = (String) getItem(position);
            View view = null;
            if (convertView == null){
                //加载子布局
                view = LayoutInflater.from(getContext()).inflate(R.layout.item_activity,null);
            }else {
                view = convertView;
            }
            //获取控件实例
            ImageView imageView = view.findViewById(R.id.img_photo);
            //设置唯一一个标识符，避免异步加载时错位
            imageView.setTag(path);
            //设置默认显示图片
            imageView.setImageResource(R.drawable.timg);
            // 根据图片URL到缓存中去找图片资源并设置
            setImageFromLruCache(path, imageView);
            return view;
        }
        /**
         * 根据图片URL地址获取缓存中图片，若不存在去磁盘缓存中查找,磁盘中没有就进行网络下载
         *
         * @param path
         * @param imageView
         */
        private void setImageFromLruCache(String path,ImageView imageView){
            //获取图片的地址
            Bitmap bitmap = lruCache.get(path);
            if (bitmap != null){
                //有缓存，直接取出图片
                Log.d(TAG, "setImageFromLruCache: 在内存缓存中找到图片" );
                imageView.setImageBitmap(bitmap);
            }else {
                // 缓存不存在，先找硬盘缓存，没有的话就去网络下载（开启异步任务）
                LoadImageAsync loadImageAsync = new LoadImageAsync();
                loadImageAsync.execute(path);
                //添加在任务列表
                tasks.add(loadImageAsync);
            }
        }
        /**
         * 取消队列中准备下载和正在下载的任务
         */
        public void cancelTask(){
            for (LoadImageAsync task : tasks){
                task.cancel(false);
            }
        }
    
    
        /**
         * 同步内存操作到journal文件
         */
        public void flushCache() {
            if (diskLruCache != null) {
                try {
                    diskLruCache.flush();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    
        class LoadImageAsync extends AsyncTask<String,Void,Bitmap>{
    
            String path = null;
            @Override
            protected Bitmap doInBackground(String... strings) {
                //图片的下载地址
                this.path = strings[0];
                DiskLruCache.Snapshot snapshot = null;
                OutputStream outputStream = null;
                Bitmap bitmap = null;
                String pathMd5 = MD5Utils.md5(path);
                //根据图片的URL查找图片是否存在于硬盘
                try {
                    snapshot = diskLruCache.get(pathMd5);
                if (snapshot == null){
                    //在磁盘缓存里没有找到对应的图片资源
                    DiskLruCache.Editor editor = diskLruCache.edit(pathMd5);
                    if (editor != null){
                        outputStream = editor.newOutputStream(0);
                        // 开启异步网络任务获取图片，并存入磁盘缓存
                        if (DownLoadToStream(path,outputStream)){
                            //下载成功
    //                        Log.d(TAG, "doInBackground: DownLoad Image Suc" );
                            editor.commit();
                        }
                    }
                }
                // 图片写入磁盘缓存后，再一次的查找磁盘缓存
                snapshot = diskLruCache.get(pathMd5);
                if (snapshot != null){
                    // 若查找到，获取图片，并把图片资源写入内存缓存
                    bitmap = BitmapFactory.decodeStream(snapshot.getInputStream(0));
                    Log.d(TAG, "doInBackground: 在磁盘缓存中找到");
                }
                    if (bitmap != null) {
                        // 将Bitmap对象添加到内存缓存当中
                        lruCache.put(path,bitmap);
                    }
                    return bitmap;
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    if (outputStream != null) {
                        try {
                            outputStream.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
                return null;
            }
    
            @Override
            protected void onPostExecute(Bitmap bitmap) {
                super.onPostExecute(bitmap);
                //根据Tag获取控件对象并设置图片
                ImageView imageView = gridView.findViewWithTag(path);
                if (imageView != null && bitmap != null) {
                    //加载图片
                    imageView.setImageBitmap(bitmap);
                }
                tasks.remove(this);
            }
            /**
             * 根据图片URL地址下载图片,成功返回true，失败false
             *
             * @param urlString
             * @param outputStream
             * @return
             */
            private boolean DownLoadToStream(String urlString,OutputStream outputStream){
                HttpURLConnection connection = null;
                BufferedInputStream inputStream = null;
                BufferedOutputStream outputStream1 = null;
    
                try {
                    final URL url = new URL(urlString);
                    connection = (HttpURLConnection) url.openConnection();
                    inputStream = new BufferedInputStream(connection.getInputStream(),8*1024);
                    outputStream = new BufferedOutputStream(outputStream,8*1024);
                    int b;
                    //读
                    while ((b = inputStream.read()) != -1){
                        //写
                        outputStream.write(b);
                    }
                    return true;
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    if (connection != null) {
                        connection.disconnect();
                    }
                    try{
                        if (outputStream != null) {
                            outputStream.close();
                        }
                        if (inputStream != null) {
                            inputStream.close();
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                return false;
            }
        }
    }

MainActivity类  
在onPause方法里进行flush操作（更新磁盘缓存操作日志，磁盘缓存之所以能够被读取取决于日志文件

package com.example.disklrucache_demo;
    
    import androidx.appcompat.app.AppCompatActivity;
    
    import android.content.Intent;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;
    import android.widget.GridView;
    import android.widget.ImageView;
    import android.widget.TextView;
    import android.widget.Toast;
    
    import com.jakewharton.disklrucache.DiskLruCache;
    
    import org.greenrobot.eventbus.EventBus;
    import org.greenrobot.eventbus.Subscribe;
    import org.greenrobot.eventbus.ThreadMode;
    
    public class MainActivity extends AppCompatActivity {
    
        public static final String TAG = "MainActivity";
        private GridView gv_photo;
        private ImageAdapter adapter;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            gv_photo= findViewById(R.id.grid_view);
            adapter = new ImageAdapter(MainActivity.this,0,Images.imageThumbUrls,gv_photo);
            gv_photo.setAdapter(adapter);
        }
    
        @Override
        protected void onPause() {
            super.onPause();
            adapter.flushCache();
        }
    
        @Override
        protected void onDestroy() {
            super.onDestroy();
            adapter.cancelTask();
        }
    }

附上效果图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyODg5NDc2_size_16_color_FFFFFF_t_70 1]

最后的话附上一个Demo下载链接

[https://download.csdn.net/download/qq\_42889476/11485297][https_download.csdn.net_download_qq_42889476_11485297]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyODg5NDc2_size_16_color_FFFFFF_t_70]: /images/20211108/27d8d92b0aff451bb199ecd0df8cd674.png
[https_download.csdn.net_download_qq_42889476_11485240]: https://download.csdn.net/download/qq_42889476/11485240
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQyODg5NDc2_size_16_color_FFFFFF_t_70 1]: /images/20211108/b47aea19ef5a48c3b12cf138062e26de.png
[https_download.csdn.net_download_qq_42889476_11485297]: https://download.csdn.net/download/qq_42889476/11485297