Android数据库

importandroid.content.ContentValues;

importandroid.content.Context;

importandroid.database.Cursor;

importandroid.database.sqlite.SQLiteDatabase;

importandroid.database.sqlite.SQLiteOpenHelper;

importandroid.os.Handler;

importandroid.os.Message;

 

/**

 * 缓存数据库

 * @author lu

 *

 */

publicclass CacheHelper extendsSQLiteOpenHelper {

 

    privatestatic final String tableName = "JSONCACHE";

    privatestatic final String URL = "URL";

    privatestatic final String JSON = "JSON";

    privatestatic final String DATE = "DATE";

 

    publicCacheHelper(Context context) {

        super(context,"cache.db",null,1);

    }

 

    @Override

    publicvoid onCreate(SQLiteDatabase db) {

        //建表jsoncache，字段：请求地址url、缓存数据json、时间date

        db.execSQL("CREATE TABLE "+tableName+" (ID INTEGER PRIMARY KEY AUTOINCREMENT, "+URL+" TEXT NOT NULL, "+JSON+" TEXT NOT NULL, "+DATE+" INTEGER NOT NULL )");

    }

 

    @Override

    publicvoid onUpgrade(SQLiteDatabase db, intoldVersion, intnewVersion) {

    }

     

    privatestatic CacheHelper helper = null;

    publicstatic CacheHelper init(Context context){

        if(helper==null) {

            helper = newCacheHelper(context);

        }

        returnhelper;

    }

     

    /**储存缓存json*/

    publicvoid setJson(finalString url0,finalString json){

        newThread(){

            publicvoid run() {

                String url = urlEncode(url0);

                ContentValues cv = newContentValues();

                cv.put(URL, url);

                cv.put(JSON, json);

                cv.put(DATE, System.currentTimeMillis());

                helper.getReadableDatabase().delete(tableName, URL+"=?",newString[]{url});

                helper.getReadableDatabase().insert(tableName,null, cv);

            }

        }.start();

    }

     

    /**获取缓存json，以handler的obj返回（懒得写监听器了）*/

    publicvoid getJson(finalString url0,finalHandler handler){

        newThread(){

            publicvoid run() {

                String url = urlEncode(url0);

                String result = null;

                Cursor c =

                helper.getReadableDatabase().query(tableName,

                        null,

                        URL+"=?",

                        newString[]{url},

                        null,

                        null,

                        null);

                if(c.moveToNext()) {

                    result = c.getString(c.getColumnIndex(JSON));

                }

                Message msg = Message.obtain();

                msg.obj = result;

                handler.sendMessage(msg);

            }

        }.start();

    }

     

    /**缓存需要定时清空*/

    publicvoid clear(){

        newThread(){

            publicvoid run() {

                helper.getReadableDatabase().delete(tableName,"ID>?",newString[]{"0"});

            }

        }.start();

    }

     

    /**url需要去掉token*/

    privateString urlEncode(String url){

        String result = url.replaceAll("accessToken.*?\\&","");

        if(result.contains("accessToken")) {//如果还没去掉，说明是在尾部

            result = result.replaceAll("\\&accessToken.*?$","");

        }

        returnresult;

    }

 

}