偶遇DiskLruCache（缓存策略解析）
浏览数：48 /
时间：2015年06月20日
根据郭神的博客写了个小demo，详细的方法都卸载注释里了，先上效果图：
布局代码：
<LinearLayout 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="com.example.disklrucache.MainActivity" >
<ScrollView
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/showSize"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="25sp" />
<Button
android:id="@+id/read"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="缓存图片" />
<Button
android:id="@+id/remove"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="移除缓存图片" />
<Button
android:id="@+id/delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="删除全部缓存（包括日志文件）"/>
<Button
android:id="@+id/show"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="显示图片" />
<ImageView
android:id="@+id/img"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
</ScrollView>
</LinearLayout>
主Activity代码
package com.example.disklrucache;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import libcore.io.DiskLruCache;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
String imageUrl = "http://img.my.csdn.net/uploads/201309/01/1378037235_7476.jpg";
private DiskLruCache lruCache = null ;
private TextView showSize ; //缓存区的大小
private ImageView img ;
private Button read,show ; //读取，与现实在屏幕上
private Button remove ; //移除缓存文件但是保留操作日志
private Button delete ; //删除缓存
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE) ;
setContentView(R.layout.activity_main);
this.read = (Button)findViewById(R.id.read) ;
this.remove = (Button)findViewById(R.id.remove) ;
this.show = (Button)findViewById(R.id.show) ;
this.delete = (Button)findViewById(R.id.delete) ;
this.showSize = (TextView) findViewById(R.id.showSize) ;
img = (ImageView) findViewById(R.id.img) ;
File file = getDiskCacheDir(MainActivity.this, "bitmap") ;
if(!file.exists()) {
file.mkdirs() ;
}
try {
lruCache = DiskLruCache.open(file, getAppVersion(MainActivity.this), 1, 10*1024*1024) ;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
this.show.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
getCacheBitmap();
showSize.setText("当前缓存尺寸："+lruCache.size());
}
});
this.read.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
new Thread(new Runnable() {
@Override
public void run() {
// TODO Auto-generated method stub
String key = hashKeyForDisk(imageUrl) ; //生成key
DiskLruCache.Editor editor;
try {
editor = lruCache.edit(key);
if(editor != null) {
OutputStream out = editor.newOutputStream(0) ;
if(downUrlToStream(imageUrl, out)) {
editor.commit();
} else {
editor.abort();
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} //将key传入editor
}
}).start();
}
});
this.remove.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
try {
String key = hashKeyForDisk(imageUrl);
lruCache.remove(key);
} catch (IOException e) {
e.printStackTrace();
}
}
});
this.delete.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
try {
lruCache.delete();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
//getCacheBitmap(); //读取下载的图片
}
/*
* 缓存的读取，主要借助get方法
*/
public void getCacheBitmap() {
try {
String key = hashKeyForDisk(imageUrl);
DiskLruCache.Snapshot snapShot = lruCache.get(key);
if (snapShot != null) {
InputStream is = snapShot.getInputStream(0);
Bitmap bitmap = BitmapFactory.decodeStream(is);
img.setImageBitmap(bitmap);
}
} catch (IOException e) {
e.printStackTrace();
}
}
/*
* 根据传入的url下载一张图片，并且将图片写入本地
*/
private boolean downUrlToStream(String url,OutputStream outputStream) {
HttpURLConnection httpurlcon = null ;
BufferedInputStream in = null ;
BufferedOutputStream out = null ;
URL mUrl;
try {
mUrl = new URL(url);
httpurlcon = (HttpURLConnection)mUrl.openConnection() ;
in = new BufferedInputStream(httpurlcon.getInputStream(),8*1024) ;
out = new BufferedOutputStream(outputStream,1024*8) ;
int b ;
while((b = in.read()) != -1) {
out.write(b);
}
return true ;
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (final IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally {
if(httpurlcon != null) {
httpurlcon.disconnect();
}
try {
if(in != null)
in.close();
if(out != null) {
out.close();
}
}catch(IOException e) {
e.printStackTrace();
}
}
return false ;
}
/*
* 调用MD5编码算法生成唯一的key
*/
public 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 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();
}
/*
* 用以获取cache目录，处理当内存卡有异常（如不在或者不可用）
*/
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);
}
/*
* 得到应用程序的版本号，作为参数传入DiskLruCache的open方法，DiskLruCache默认
* 程序版本号发生变化时移除全部缓存数据
*/
public int getAppVersion(Context context) {
PackageInfo version;
try {
version = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
return version.versionCode ;
} catch (NameNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return 1 ; //程序发生异常时返回初始版本号1.0
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
try {
lruCache.flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
super.onPause();
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
try {
lruCache.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
super.onDestroy();
}
}
最后不要忘了声明权限
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
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