Android中图片的三级缓存机制

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<ImageView
android:id="@+id/iv_img"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@mipmap/ic_launcher"
android:layout_centerInParent="true"/>
<Button
android:id="@+id/btn_download"
android:layout_below="@+id/iv_img"
android:layout_centerHorizontal="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="加载图片"/>
</RelativeLayout>

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

package com.yztc.lx.cashimg;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
/**网络访问工具类
* Created by Lx on 2016/8/19.
*/
public class HttpUtils {
/**
* 判断网络连接是否通畅
* @param mContext
* @return
*/
public static boolean isNetConn(Context mContext) {
ConnectivityManager manager = (ConnectivityManager) mContext.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo info = manager.getActiveNetworkInfo();
if (info != null) {
return info.isConnected();
} else {
return false;
}
}
/**
* 根据path下载网络上的数据
* @param path 路径
* @return 返回下载内容的byte数据形式
*/
public static byte[] getDateFromNet(String path) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setDoInput(true);
conn.connect();
if (conn.getResponseCode()==200) {
InputStream is = conn.getInputStream();
byte b[] = new byte[1024];
int len;
while ((len=is.read(b))!=-1) {
baos.write(b, 0, len);
}
return baos.toByteArray();
}
} catch (IOException e) {
e.printStackTrace();
}
return baos.toByteArray();
}
}

package com.yztc.lx.cashimg;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
/**
* Created by Lx on 2016/8/20.
*/
public class ExternalStorageUtils {
/**
* 将传递过来的图片byte数组存储到sd卡中
* @param imgName 图片的名字
* @param buff byte数组
* @return 返回是否存储成功
*/
public static boolean storeToSDRoot(String imgName, byte buff[]) {
boolean b = false;
String basePath = Environment.getExternalStorageDirectory().getAbsolutePath();
File file = new File(basePath, imgName);
try {
FileOutputStream fos = new FileOutputStream(file);
fos.write(buff);
fos.close();
b = true;
} catch (IOException e) {
e.printStackTrace();
}
return b;
}
/**
* 从本地内存中根据图片名字获取图片
* @param imgName 图片名字
* @return 返回图片的Bitmap格式
*/
public static Bitmap getImgFromSDRoot(String imgName) {
Bitmap bitmap = null;
String basePath = Environment.getExternalStorageDirectory().getAbsolutePath();
File file = new File(basePath, imgName);
try {
FileInputStream fis = new FileInputStream(file);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte b[] = new byte[1024];
int len;
while ((len = fis.read(b)) != -1) {
baos.write(b, 0, len);
}
byte buff[] = baos.toByteArray();
if (buff != null && buff.length != 0) {
bitmap = BitmapFactory.decodeByteArray(buff, 0, buff.length);
}
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
}

package com.yztc.lx.cashimg;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.util.LruCache;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import java.lang.ref.SoftReference;
import java.util.LinkedHashMap;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private Button btn_download;
private ImageView iv_img;
private MyLruCache myLruCache;
private LinkedHashMap<String, SoftReference<Bitmap>> cashMap = new LinkedHashMap<>();
private static final String TAG = "MainActivity";
private String imgPath = "http://www.3dmgame.com/UploadFiles/201212/Medium_20121217143424221.jpg";
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
Bitmap bitmap = (Bitmap) msg.obj;
iv_img.setImageBitmap(bitmap);
Toast.makeText(MainActivity.this, "从网络上下载图片", Toast.LENGTH_SHORT).show();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
int totalMemory = (int) Runtime.getRuntime().maxMemory();
int size = totalMemory / 8;
myLruCache = new MyLruCache(size);
btn_download.setOnClickListener(this);
}
private void initView() {
btn_download = (Button) findViewById(R.id.btn_download);
iv_img = (ImageView) findViewById(R.id.iv_img);
}
@Override
public void onClick(View v) {
Bitmap b = getImgCache();
if (b != null) {
iv_img.setImageBitmap(b);
} else {
new Thread(new Runnable() {
@Override
public void run() {
if (HttpUtils.isNetConn(MainActivity.this)) {
byte b[] = HttpUtils.getDateFromNet(imgPath);
if (b != null && b.length != 0) {
Bitmap bitmap = BitmapFactory.decodeByteArray(b, 0, b.length);
Message msg = Message.obtain();
msg.obj = bitmap;
handler.sendMessage(msg);
myLruCache.put(imgPath, bitmap);
Log.d(TAG, "run: " + "缓存到强引用中成功");
boolean bl = ExternalStorageUtils.storeToSDRoot("haha.jpg", b);
if (bl) {
Log.d(TAG, "run: " + "缓存到本地内存成功");
} else {
Log.d(TAG, "run: " + "缓存到本地内存失败");
}
} else {
Toast.makeText(MainActivity.this, "下载失败！", Toast.LENGTH_SHORT).show();
}
} else {
Toast.makeText(MainActivity.this, "请检查你的网络！", Toast.LENGTH_SHORT).show();
}
}
}).start();
}
}
/**
* 从缓存中获取图片
*
* @return 返回获取到的Bitmap
*/
public Bitmap getImgCache() {
Bitmap bitmap = myLruCache.get(imgPath);
if (bitmap != null) {
Log.d(TAG, "getImgCache: " + "从LruCache获取图片");
} else {
SoftReference<Bitmap> sr = cashMap.get(imgPath);
if (sr != null) {
bitmap = sr.get();
myLruCache.put(imgPath, bitmap);
cashMap.remove(imgPath);
Log.d(TAG, "getImgCache: " + "从软引用获取图片");
} else {
bitmap = ExternalStorageUtils.getImgFromSDRoot("haha.jpg");
Log.d(TAG, "getImgCache: " + "从外部存储获取图片");
}
}
return bitmap;
}
/**
* 自定义一个方法继承系统的LruCache方法
*/
public class MyLruCache extends LruCache<String, Bitmap> {
/**
* 必须重写的构造函数，定义强引用缓存区的大小
* @param maxSize for caches that do not override {@link #sizeOf}, this is
* the maximum number of entries in the cache. For all other caches,
* this is the maximum sum of the sizes of the entries in this cache.
*/
public MyLruCache(int maxSize) {
super(maxSize);
}
//返回每个图片的大小
@Override
protected int sizeOf(String key, Bitmap value) {
//获取当前变量每行的字节数和行高度（基本是固定写法，记不住给我背！）
return value.getRowBytes() * value.getHeight();
}
/**
* 当LruCache中的数据被驱逐或是移除时回调的函数
*
* @param evicted 当LruCache中的数据被驱逐用来给新的value倒出空间的时候变化
* @param key 用来标示对象的键，一般put的时候传入图片的url地址
* @param oldValue 之前存储的旧的对象
* @param newValue 存储的新的对象
*/
@Override
protected void entryRemoved(boolean evicted, String key, Bitmap oldValue, Bitmap newValue) {
if (evicted) {
/**
* 将旧的值存到软引用中，因为强引用中可能有多个值被驱逐，
* 所以创建一个LinkedHashMap<String, SoftReference<Bitmap>>来存储软引用
* 基本也是固定写法
*/
SoftReference<Bitmap> softReference = new SoftReference<Bitmap>(oldValue);
cashMap.put(key, softReference);
}
}
}
}