Android本地缓存DiskLruCache完整详细学习示例

浏览数：72 / 时间：2015年06月11日
MainActivity如下:
package cc.vv;

import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;

import libcore.io.DiskLruCache;
import libcore.io.Utils;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
/**
 * Demo描述:
 * DiskLruCache学习示例
 * 
 * DiskLruCache用于本地缓存.
 * 比如在网络可用时加载一张网络图片，当网络不可用时依然可以显示该图片。
 * 实现的原理是将图片保存到本地；当网络不可用时从本地加载图片。
 * 在此简单模拟该过程，步骤如下:
 * 1 从网络下载图片且保存至DiskLruCache
 * 2 从DiskLruCache中获取缓存图片进行显示
 * 
 * 
 * 学习备注:
 * 1 DiskLruCache的本地缓存文件路径为:
 *   /sdcard/Android/data/<application package>/cache
 *   当应用被卸载时该文件亦会被删除
 * 2 新闻类APP一般的做法.从新闻列表(ListView)中点击某条新闻跳转到详细画面.
 *   在详细画面一般有图片和文字.此时可以将图片和文字用同一个key存到不同的缓存文件夹下.
 *   在断网时浏览该新闻时候依据该key分别取出对应的图片和文字即可.
 * 3 在示例中用到了DiskLruCache的存和取的相关API.在此对其余重要API简要整理:
 *   3.1 remove(String key) 删除某个已缓存的对象.
 *   3.2 size() 得到缓存路径下缓存的总大小.这个很常见.许多APP都提示当前有多少缓存.
 *   3.3 flush() 将内存中的操作记录同步到日志文件(也就是journal文件)中
 *       一般在Activity的onPause()中调用该方法.
 *   3.4 close() 关闭DiskLruCache.该方法与open方法对应.
 *       一般在Activity的onDestory()中调用该方法.
 *   3.5 delete() 将缓存数据全部删除.
 *   
 * 
 * 学习资源:
 * http://blog.csdn.net/guolin_blog/article/details/28863651
 * Thank you very much
 */
public class MainActivity extends Activity {
	private ImageView mImageView;
    private DiskLruCache mDiskLruCache;
    private Context mContext;
    //DiskLruCache中对于图片的最大缓存值.
    private int maxSize=20*1024*1024;
    private String mImagePath="http://www.baidu.com/img/bdlogo.png";
    private Handler mHandler;
    private final int FINISH=9527;
    
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		init();
	}
	
	private void init(){
		try {
			mHandler = new Handler() {
				@Override
				public void handleMessage(Message msg) {
					super.handleMessage(msg);
					if (msg.what==FINISH) {
						getDataFromDiskLruCache();
					}
				}
			};
			mContext=this;
			mImageView=(ImageView) findViewById(R.id.imageView);
			
			initDiskLruCache();
			
		} catch (Exception e) {
			// TODO: handle exception
		}
	}
	
	
	/**
	 * 初始化DiskLruCache
	 */
	private void initDiskLruCache(){
		try {
			File cacheDir=Utils.getDiskLruCacheDir(mContext, "bitmap");
			if (!cacheDir.exists()) {
				cacheDir.mkdirs();
			}
			int versionCode=Utils.getAppVersionCode(mContext);
			mDiskLruCache=DiskLruCache.open(cacheDir, versionCode, 1, maxSize);
			
			saveDataToDiskLruCache();
			
		} catch (Exception e) {
			// TODO: handle exception
		}
	}
	
	
	// 将数据写入DiskLruCache
	private void saveDataToDiskLruCache() {
		new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					//第一步:获取将要缓存的图片的对应唯一key值.
					String key = Utils.getStringByMD5(mImagePath);
					//第二步:获取DiskLruCache的Editor
					DiskLruCache.Editor editor = mDiskLruCache.edit(key);
					if (editor!=null) {
						//第三步:从Editor中获取OutputStream
						OutputStream outputStream=editor.newOutputStream(0);
						//第四步:下载网络图片且保存至DiskLruCache图片缓存中
						boolean isSuccessfull=Utils.getBitmapFromNetWorkAndSaveToDiskLruCache(mImagePath, outputStream);
						if (isSuccessfull) {
							editor.commit();
							mHandler.sendEmptyMessage(FINISH);
						}else{
							editor.abort();
						}
						mDiskLruCache.flush();
					}
				} catch (Exception e) {
					
				}

			}
		}).start();
	}
	
	
	//从DiskLruCache中读取数据
	private void getDataFromDiskLruCache(){
		try {
			//第一步:获取已缓存的图片的对应唯一key值.
			String key = Utils.getStringByMD5(mImagePath);
			//第二步:依据key获取到其对应的snapshot
			DiskLruCache.Snapshot snapshot=mDiskLruCache.get(key);
			if (snapshot!=null) {
				//第三步:从snapshot中获取到InputStream
				InputStream inputStream=snapshot.getInputStream(0);
				Bitmap bitmap=BitmapFactory.decodeStream(inputStream);
				mImageView.setImageBitmap(bitmap);
			}
		} catch (Exception e) {
			
		}
		
	}

}

Utils如下:

package libcore.io;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.http.HttpStatus;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Environment;

public class Utils {

	/**
	 * 获取DiskLruCache的缓存文件夹
	 * 注意第二个参数dataType
	 * DiskLruCache用一个String类型的唯一值对不同类型的数据进行区分.
	 * 比如bitmap,object等文件夹.其中在bitmap文件夹中缓存了图片.
	 * 
	 * 缓存数据的存放位置为:
	 * /sdcard/Android/data/<application package>/cache 
	 * 如果SD卡不存在时缓存存放位置为:
	 * /data/data/<application package>/cache
	 * 
	 */
	public static File getDiskLruCacheDir(Context context, String dataType) {
		String dirPath;
		File cacheFile = null;
		if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
			!Environment.isExternalStorageRemovable()) {
			dirPath=context.getExternalCacheDir().getPath();
		} else {
			dirPath=context.getCacheDir().getPath();
		}
		cacheFile=new File(dirPath+File.separator+dataType);
		return cacheFile;
	}
	
	
	
	/**
	 * 获取APP当前版本号
	 * @param context
	 * @return
	 */
	public static int getAppVersionCode(Context context){
		int versionCode=1;
		try {
			String packageName=context.getPackageName();
			PackageManager packageManager=context.getPackageManager();
			PackageInfo packageInfo=packageManager.getPackageInfo(packageName, 0);
			versionCode=packageInfo.versionCode;
		} catch (NameNotFoundException e) {
			e.printStackTrace();
		}
		return versionCode;
	}
	
	
	/**
	 * 将字符串用MD5编码.
	 * 比如在改示例中将url进行MD5编码
	 */
	public static String getStringByMD5(String string) {
		String md5String = null;
		try {
			// Create MD5 Hash
			MessageDigest messageDigest = MessageDigest.getInstance("MD5");
			messageDigest.update(string.getBytes());
			byte messageDigestByteArray[] = messageDigest.digest();
			if (messageDigestByteArray == null || messageDigestByteArray.length == 0) {
				return md5String;
			}

			// Create hexadecimal String
			StringBuffer hexadecimalStringBuffer = new StringBuffer();
			int length = messageDigestByteArray.length;
			for (int i = 0; i < length; i++) {
				hexadecimalStringBuffer.append(Integer.toHexString(0xFF & messageDigestByteArray[i]));
			}
			md5String = hexadecimalStringBuffer.toString();
			return md5String;
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		return md5String;
	}
	
	
	/**
	 * 从网络获取图片且保存至SD卡中的缓存
	 */
	public static boolean getBitmapFromNetWorkAndSaveToDiskLruCache(String imageUrl,OutputStream outputStream){
		boolean isSuccessfull=false;
		URL url=null;
		HttpURLConnection httpURLConnection=null;
		BufferedOutputStream bufferedOutputStream=null;
		InputStream inputStream=null;
		BufferedInputStream bufferedInputStream=null;
		try {
			url=new URL(imageUrl);
			httpURLConnection=(HttpURLConnection) url.openConnection();
			httpURLConnection.setConnectTimeout(5*1000);
			httpURLConnection.setReadTimeout(10*1000);
			httpURLConnection.setDoInput(true);
			httpURLConnection.setDoOutput(true);
			if (httpURLConnection.getResponseCode()==HttpStatus.SC_OK) {
				bufferedOutputStream=new BufferedOutputStream(outputStream);
				inputStream=httpURLConnection.getInputStream();
				bufferedInputStream=new BufferedInputStream(inputStream);
				int len=0;
				byte [] buffer=new byte[1024];
				while((len=bufferedInputStream.read(buffer))!=-1){
					bufferedOutputStream.write(buffer, 0, len);
					bufferedOutputStream.flush();
				}
				isSuccessfull=true;
			} else {
				isSuccessfull=false;
				System.out.println("图片请求失败");
			}
		} catch (Exception e) {
			    isSuccessfull=false;
			    System.out.println("e="+e.toString());
		}finally{
			try {
				if (bufferedOutputStream!=null) {
					bufferedOutputStream.close();
				}
				if (inputStream!=null) {
					inputStream.close();
				}
				if (bufferedInputStream!=null) {
					bufferedInputStream.close();
				}
				if (httpURLConnection!=null) {
					httpURLConnection.disconnect();
				}
			} catch (Exception e) {
				 System.out.println("e="+e.toString());
			}
		}
		
		return isSuccessfull;
		
	}

}

main.xml如下: 

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" />

</RelativeLayout>


郑重声明：本站内容如果来自互联网及其他传播媒体，其版权均属原媒体及文章作者所有。转载目的在于传递更多信息及用于网络分享，并不代表本站赞同其观点和对其真实性负责，也不构成任何其他建议。

标签： Android iOS 移动互联 终端开发

相关文章

随机文章

您可能还喜欢

您可能还喜欢