在Android图片缓存

在Android中经常性的会用到加载图片的问题，那么为了不阻塞主线程，我们首先要考虑异步操作，为了用户更好地体验我们还需要考虑对图片进行缓存。

对图片进行缓存首先要了解softreference<Bitmap>软存储机制，还有就是硬存储的方式在手机端一般就是SD卡的存储。

那么如果当我们进行图片异步加载的时候就需要考虑内存中是否有，如果内存中有的话直接从内存中取出，如果内存中没有的话，再从网上去下载。

判断内存中是否有图片要先从softreference中判断,如果没有就从SD卡中读取，如果两者都没有则从网上下载

ImgLoader.java

package com.SQLiteTest;

import java.io.FileInputStream;
import java.lang.ref.SoftReference;
import java.util.Map;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;

public class PicManager {
    private Context context;
    private Map<String, SoftReference<Bitmap>> imgCache;
    private FileUtils fUtils=new FileUtils();

    /*
     * 构造函数
     */
    public PicManager(Context context,
            Map<String, SoftReference<Bitmap>> imgCache) {
        super();
        this.context = context;
        this.imgCache = imgCache;
    }

    /*
     * 先从缓存中读取，如果没有的话从文件读取
     */

    public Bitmap getFromCache(String url)
    {
        Bitmap bit=null;
        if(imgCache.containsKey(url))
        {

            synchronized (imgCache) {
                SoftReference<Bitmap> bitReference=imgCache.get(url);
                if(bitReference!=null)
                {
                    bit=bitReference.get();
                }

            }

        }
        else {
            bit=getFromSDcard(url);
            imgCache.put(url, new SoftReference<Bitmap>(bit));
        }
        return bit;
    }

    private Bitmap getFromSDcard(String url)
    {

        Bitmap bitmap=null;

        String filename=fUtils.getFName(url);

        System.out.println("PicManager-->"+filename);
        String path=Environment.getExternalStorageDirectory()+"/";
        try {
              FileInputStream fis=context.openFileInput(path+"picture/"+filename);
            //FileInputStream fis=new FileInputStream(path+"picture"+filename);
            bitmap=BitmapFactory.decodeStream(fis);
            fis.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return bitmap;
    }
}

 

PicManager.java

package com.SQLiteTest;

import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;

public class ImgLoader {

    private Context context;
    final  Map<String, SoftReference<Bitmap>> imgCache=
            new HashMap<String, SoftReference<Bitmap>>();

    public ImgLoader(Context context) {
        super();
        this.context = context;
    }

    private Handler mhandler=new Handler();
    private PicManager pm=new PicManager(context, imgCache);
    private FileUtils fuUtils=new FileUtils();
    private ExecutorService threadPool=Executors.newFixedThreadPool(5);
    private DownLoad dl=new DownLoad();

    public Bitmap loadImg(final String url,final ImgCallBack callBack)
    {
        Bitmap bitmap=null;
        try {

            bitmap=pm.getFromCache(url);
            System.out.println("ImgLoader--->执行？？？  ");
            if(bitmap==null)
            {
                System.out.println("ImgLoader--->什么时候执行");
                threadPool.submit(new Runnable() {

                    @Override
                    public void run() {
                        // TODO Auto-generated method stub
                        String fname=fuUtils.getFName(url);

                        dl.download(url,"picture/", fname);
                        final Bitmap bit=BitmapFactory.decodeStream(dl.getInput(url));
                        //imgCache.put(url,new SoftReference<Bitmap>(bit));
                        mhandler.post(new Runnable() {

                            @Override
                            public void run() {
                                // TODO Auto-generated method stub

                                callBack.refresh(bit);
                            }
                        });
                    }


                });
            }
        } catch (Exception e) {
            // TODO: handle exception
        }

        return bitmap;
    }

}

DownLoad.java

 

package com.SQLiteTest;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownLoad {


    public void download(String url,String path,String filename)
    {
        FileUtils fUtils=new FileUtils();
        InputStream input=null;

        if(!fUtils.isExist(filename))
        {
            try
            {
                input=getInput(url);
                System.out.println("DownLoad--->"+input);
                fUtils.write2SDCARD(path, filename, input);

            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }


        }


    }

    public InputStream getInput(String urlstr)
    {
        URL url=null;
        InputStream input=null;
        try {
            url = new URL(urlstr);
            HttpURLConnection hul=(HttpURLConnection)url.openConnection();
            input=hul.getInputStream();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return input;
    }
}

FileUtilts.java

 

package com.SQLiteTest;

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

import android.os.Environment;

public class FileUtils {

    private String SDPATH=Environment.getExternalStorageDirectory()+"/";

    public File creaPath(String path)
    {
        File file=new File(SDPATH+path);
        file.mkdir();
        return file;
    }

    public File creaFile(String fileName) throws Exception
    {
        File f=new File(SDPATH+fileName);
        f.createNewFile();
        return f;
    }

    public boolean isExist(String Filename)
    {
        File f=new File(SDPATH+Filename);
        return f.exists();
    }

    public void write2SDCARD(String path,String filename,InputStream input)
    {

        try {
            creaPath(path);
            File file =creaFile(path+filename);

            OutputStream output=new FileOutputStream(file);
            byte[] buffer=new byte[4*1024];
            int line=0;
            while((line=input.read(buffer))!=-1)
            {
                output.write(buffer,0, line);

            }
            output.flush();
            output.close();

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public String getFName(String url)
    {
        int start=url.lastIndexOf("/");

        String str=url.substring(start);
        return str;
    }


}

ImgCallBack.java

这是个接口主要负责刷新Bitmap

package com.SQLiteTest;

import android.graphics.Bitmap;

public interface ImgCallBack {

    public void refresh(Bitmap bitmap);

}