c)缓存真正需要的数据。不要觉外存是无限的，所以就可以什么都存，要知道，多则繁，繁则乱。曾经有一同事，每天存几百MB的用户数据(所有用户的性别、 age、联系方式等等)，而PM需要的只是一个每日数户的活跃数据报表，于是最后改为缓存每天的用户分析报表数据即可(才10几KB)。

d)给缓存文件加密。最简单就是去掉文件的扩展名，这也算加密，当然，你可以把服务端文件加密，然后在内存中解密。这就看项目的需求而定，我的经验也不足，一般就是改改扩展名之类的。

网络图片在开发过程中，一般都将图片缓存到本地sd卡中（经常要使用的图片），方便下次直接引用而不再次请求网络耗费资源。而如果是自己开发搜索功能里有涉及到图片的显示，可以直接Map<String, SoftReference<Drawable>>，即软引用。软引用重要代码代码：package com.test.load;import java.lang.ref.SoftReference;import java.net.URL;import java.util.HashMap;import java.util.Map;import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message;public class ThreadImgLoader {private Map<String, SoftReference<Drawable>> imageCache=new HashMap<String, SoftReference<Drawable>>();public Drawable loadDrawable(final String imgUrl, final ImageCallback callback){if (imageCache.containsKey(imgUrl)) {SoftReference<Drawable> sf=imageCache.get(imgUrl);if (sf.get()!=null) {return sf.get();}}final Handler handler=new Handler(){public void handleMessage(Message msg) {callback.imageLoaded((Drawable) msg.obj);}};new Thread(){public void run() {Drawable drawable=loadImgFromUrl(imgUrl);if (drawable!=null) {imageCache.put(imgUrl, new SoftReference<Drawable>(drawable));Message msg=handler.obtainMessage(0, drawable);handler.sendMessage(msg);}}}.start();return null;}public Drawable loadImgFromUrl(String imgUrl) {try {return Drawable.createFromStream(new URL(imgUrl).openStream(), "src");} catch (Exception e) {return null;}}public interface ImageCallback{public void imageLoaded(Drawable drawable);}}下面是缓存到SD卡的重要代码，当然你也可以搜索一下，这方面的东西很多。WeakHashMap也是使用了软引用，你可以去看它的源代码：package com.test;import java.io.File;import java.io.FileOutputStream;import java.io.OutputStream;import java.util.WeakHashMap;import android.graphics.Bitmap;import android.graphics.Bitmap.CompressFormat;import android.graphics.BitmapFactory;import android.os.Environment;public class MyImgCache extends WeakHashMap<String, Bitmap> {private static MyImgCache myImgCache=new MyImgCache();private static final String CACHE_FILE="/MyXiaoCaiImg";public static MyImgCache getInstance(){return myImgCache;}public boolean isBitmapExist(String url) {boolean isexist=false;String name=changeUrlName(url);String filePath=isMakeFile();File file=new File(filePath, name);if (containsKey(url)) {isexist=true;}else if (file.exists()) {String path=file.getAbsolutePath();System.out.println(path);Bitmap bitmap=BitmapFactory.decodeFile(path);if (bitmap!=null) {put(url, bitmap, false);isexist=true;}}return isexist;}private String changeUrlName(String url) {String name = url.replaceAll(":", "_");name = name.replaceAll("//", "_");name = name.replaceAll("/", "_");name = name.replaceAll("=", "_");name = name.replaceAll(",", "_");name = name.replaceAll("&", "_");return name;}private String isMakeFile() {String rootpath = null;if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {rootpath = Environment.getExternalStorageDirectory().toString();}String filepath = rootpath + CACHE_FILE;File file = new File(filepath);if (!file.exists()) {file.mkdirs();}return filepath;}public Bitmap put(String key, Bitmap value) {String name=changeUrlName(key);String filePath=isMakeFile();File file = new File(filePath, name);OutputStream outputStream = null;try {outputStream = new FileOutputStream(file);value.compress(CompressFormat.JPEG, 100, outputStream);outputStream.flush();outputStream.close();outputStream = null;} catch (Exception e) {e.printStackTrace();}return super.put(key, value);}public Bitmap put(String key, Bitmap value, boolean b) {if (b) {return this.put(key, value);}else {return super.put(key, value);}}}