android实现服务器图片本地缓存

情况：在做ostocy-jshop开源系统的时候，需要做一个关于android如何进行服务器图片本地缓存的功能。我使用了如下几个东西。

 

1,android 本地数据库SQLite

        2,android下载网络图片

3,正则截取

4,Bitmap保存到本地

 

那就一个一个来说说吧

 

1,android 本地数据库SQLite：我要建立一个本地数据库，用来存放服务器返回的数据，缓存起来，下次就读取这个SQLite数据库了。

 

看代码先，然后解释

 

public class DBHelper extends SQLiteOpenHelper {
	
	//数据库名称
	public static final String DB_NAME="jshopmactive.db";
	
	//商品表名称
	public static final String GOODS_TM_NAME="goods_tm";
	

	//创建商品sql
	private static final String CREATE_GOODS_TM="create table "
		+"goods_tm(_id integer primary key autoincrement,goodsCategoryTid text,goodsid text,goodsname text,memberprice text,pictureurl text)";
	
	
	private SQLiteDatabase db;
	
	
	
	public DBHelper(Context context) {
		super(context, DB_NAME, null, 3);
		// TODO Auto-generated constructor stub
	}
	@Override
	public void onCreate(SQLiteDatabase db) {
		this.db=db;
		db.execSQL(CREATE_GOODS_TM);
	}

	public void createDB(){
		db=this.getWritableDatabase();
		db.execSQL(CREATE_GOODS_TM);
	}
	
	
	/**
	 * 插入数据
	 * @param values
	 * @param tablename
	 */
	public void insert(String tablename,ContentValues values){
		SQLiteDatabase db=this.getWritableDatabase();
		db.insert(tablename, null, values);
		db.close();
	}
	
	/**
	 * 查询数据
	 * @param tablename
	 * @return
	 */
	public Cursor query(String tablename){
		SQLiteDatabase db=this.getWritableDatabase();
		Cursor c=db.query(tablename, null, null, null, null, null, null);
		return c;
	}
	
	/**
	 * 查询数据
	 * @param tablename
	 * @return
	 */
	public Cursor queryByParam(String tablename,String param){
		SQLiteDatabase db=this.getWritableDatabase();
		Cursor c=db.rawQuery("select * from "+tablename+" where goodsCategoryTid=?", new String[]{String.valueOf(param)}); 
		return c;
	}
	
	/**
	 * 删除数据
	 * @param talbename
	 * @param id
	 */
	public void delete(String talbename,String id){
		if(db==null){
			db=this.getWritableDatabase();
			db.delete(talbename, "_id=?", new String[]{String.valueOf(id)});
		}
	}
	/**
	 * 删除所有数据
	 * @param tablename
	 */
	public void deleteAll(String tablename){
		if(db==null){
			db=this.getWritableDatabase();
			db.delete(tablename, null, null);
		}
	}
	
	/**
	 * 删除数据库表
	 * @param tablename
	 */
	public void DropTable(String tablename){
		db=this.getWritableDatabase();
		db.execSQL("drop table "+tablename);
	}
	/**
	 * 删除数据库
	 * @param tablename
	 */
	public void DropDB(){
		db=this.getWritableDatabase();
//		db.execSQL("drop database jshopmactive");
		onUpgrade(db,3,4);
	}
	
	/**
	 * 关闭数据库连接
	 */
	public void close(){
		if(db!=null){
			db.close();
		}
	}
	
	
	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		// TODO Auto-generated method stub
		db.execSQL("DROP TABLE IF EXISTS "+TABLE_TM_NAME);
		db.execSQL("DROP TABLE IF EXISTS "+GOODS_CATEGORY_TM_NAME);
		db.execSQL("DROP TABLE IF EXISTS "+GOODS_TM_NAME);
        onCreate(db);
	}

}

 这里主要就是在建立数据表，抽取了一部分代码。

 

2,android下载网络图片：我通过android访问基于http的服务器方法，获取一个有图片的信息。

 

看代码

 

public ArrayList<HashMap<String, Object>> getGoodsList(String goodsCategoryTid) throws IOException {
		requestjsonstr = this.queryGoodsListForJshop(goodsCategoryTid);
		if (Validate.StrNotNull(requestjsonstr)) {
			JSONArray ja = (JSONArray) JSONValue.parse(requestjsonstr);
			for (int i = 0; i < ja.size(); i++) {
				HashMap<String, Object> map = new HashMap<String, Object>();
				JSONObject jo = (JSONObject) (ja.get(i));
				map.put("pictureurl",getPictureurlImg(JshopActivityUtil.BASE_URL+ jo.get("pictureurl").toString()));
				map.put("goodsname", jo.get("goodsname").toString());
				map.put("memberprice", "￥" + jo.get("memberprice").toString());
				map.put("goodsid", jo.get("goodsid").toString());
				map.put("goodsCategoryTid", goodsCategoryTid);
				map.put("pictureurlpath", downloadpcurl);
				goodslists.add(map);
			}
		}
		return goodslists;
	}

	private Bitmap getPictureurlImg(String pictureurl) throws IOException {
		URL url = new URL(pictureurl);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setRequestMethod("GET");
		conn.setConnectTimeout(5 * 1000);
		InputStream in = conn.getInputStream();
		Bitmap bm = BitmapFactory.decodeStream(in);
		// 保存本地图片
		String fileName=savePicturetoDeviceAndReturnFixedUrl(pictureurl);
		saveOnlinePictureToCard(bm,fileName);
		in.close();
		return bm;

	}

 

3,正则截取

 

/**
	 * 获取网络图片名称
	 * 
	 * @param pictureurl
	 * @return
	 */
	private String savePicturetoDeviceAndReturnFixedUrl(String pictureurl) {
		
		String regstr = "(http:|https:)\\/\\/[\\S\\.:/]*\\/(\\S*)\\.(jpg|png|gif)";
		String postfix = "", filename = "", resultstr = "";
		Pattern patternForImg = Pattern.compile(regstr,Pattern.CASE_INSENSITIVE);
		Matcher matcher = patternForImg.matcher(pictureurl);
		if (matcher.find()) {
			filename = matcher.group(2);
			postfix = matcher.group(3);
		}
		return resultstr = filename + "." + postfix;
	}

 

4,Bitmap保存到本地

 

private void saveOnlinePictureToCard(Bitmap bm, String fileName)
			throws IOException {
		File dirFile = new File(JshopMParams.SAVEPCPATH);
		if (!dirFile.exists()) {
			dirFile.mkdir();
		}
		String onlineFilePath = JshopMParams.SAVEPCPATH +fileName;
		File myOnlineFile = new File(onlineFilePath);
		BufferedOutputStream bos = new BufferedOutputStream(
				new FileOutputStream(myOnlineFile));
		bm.compress(Bitmap.CompressFormat.JPEG, 100, bos);
		bos.flush();
		bos.close();
		this.downloadpcurl = onlineFilePath;
	}

 

详情请见https://github.com/sdywcd/ostocy-jshop 开源项目