无网时数据库缓存_无网络数据库存储-优快云博客

本博客介绍了一个安卓应用如何实现网络数据的获取、解析及本地缓存功能。应用通过HTTP请求获取JSON格式的文章列表，并利用Gson库解析数据。此外，还实现了Pull-to-Refresh下拉刷新功能，并在无网络时自动读取本地数据库中缓存的数据。

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数据库

package com.bwie.com.moniyuekao01.db;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

/**
 * Created by Administrator on 2018/4/3.
 */

public class JsonDao {

    private final MyHelp myHelp;

    public JsonDao(Context context){
        myHelp = new MyHelp(context);

    }
    //添加的方法
    public void insertData(String path,String json){
        //得到一个可读可写的数据库
        SQLiteDatabase sqLiteDatabase = myHelp.getWritableDatabase();

        //先删除 后加入
        sqLiteDatabase.delete("JsonDao","urlpath=?",new String[]{path});

        ContentValues contentValues=new ContentValues();
        //key值是数据表中的列名
        contentValues.put("urlpath",path);
        contentValues.put("jsondata",json);

        //第二个参数 ，强制要插入的null值的列的列名
        long rowid = sqLiteDatabase.insert("JsonDao", null, contentValues);
        Log.d("zzz","插入的数据rowid:"+rowid);

    }
    //查询的方法
    public String questData(String path){
        Log.d("zzz","--正在查询数据--");
        String data="";
        SQLiteDatabase database = myHelp.getWritableDatabase();
        Cursor cursor = database.query("JsonDao", null, "urlpath=?", new String[]{path}, null, null, null);
        while (cursor.moveToNext()){
            data=cursor.getString(cursor.getColumnIndex("jsondata"));
        }
        return data;
    }

}

MyHelp类

package com.bwie.com.moniyuekao01.db;

import android.content.Context;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * Created by Administrator on 2018/4/4.
 */

public class MyHelp extends SQLiteOpenHelper {
    //构造数据库名
    public MyHelp(Context context) {
        super(context,"db",null, 1);
    }


    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL("create table JsonDao(id integer primary key autoincrement,urlpath text,jsondata text)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {

    }
}

主方法

package com.bwie.com.moniyuekao01;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import android.widget.Toast;

import com.bwie.com.moniyuekao01.db.JsonDao;
import com.bwie.com.moniyuekao01.utiles.NetStateUtil;
import com.bwie.com.moniyuekao01.utiles.StreamToString;
import com.google.gson.Gson;
import com.handmark.pulltorefresh.library.PullToRefreshBase;
import com.handmark.pulltorefresh.library.PullToRefreshListView;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private PullToRefreshListView ptrlv;
    private int pageIndex=1;
    private int operType=1;
    private String netUrl="https://api.tianapi.com/wxnew/?key=48a7d7193e11bd2dd4a683b6e2f90a4f&num=10&page="+pageIndex;
    private Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            List<ResultData.NewslistBean> newslist= (List<ResultData.NewslistBean>) msg.obj;
            showData(newslist);
        }


    };
    private List<ResultData.NewslistBean> alldata=new ArrayList<>();
    private JsonDao jsonDao;
    private MyAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ptrlv = findViewById(R.id.ptrlv);

       //构造Dao类
        jsonDao = new JsonDao(this);

        //初始化pulltoRefresh框架
        initPlv();

        requstData();

    }
    private void showData(List<ResultData.NewslistBean> list) {
        if(operType==1){
           alldata.clear();//清空集合中的所有数据
        }
        alldata.addAll(list);
        //设置适配器
        setLvAdapter();

        //关闭头尾刷新视图
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                ptrlv.onRefreshComplete();
            }
        },1000);

    }

    private void setLvAdapter() {
        if (adapter==null){
            adapter = new MyAdapter(MainActivity.this,alldata);
            ptrlv.setAdapter(adapter);
        }else {
            //刷新
            adapter.notifyDataSetChanged();
        }
    }

    private void initPlv() {
        ptrlv.setMode(PullToRefreshBase.Mode.BOTH);

        ptrlv.setOnRefreshListener(new PullToRefreshBase.OnRefreshListener2<ListView>() {
            @Override
            public void onPullDownToRefresh(PullToRefreshBase<ListView> pullToRefreshBase) {
                operType=1;
                pageIndex=1;
                netUrl="https://api.tianapi.com/wxnew/?key=48a7d7193e11bd2dd4a683b6e2f90a4f&num=10&page="+pageIndex;
                requstData();
            }

            @Override
            public void onPullUpToRefresh(PullToRefreshBase<ListView> pullToRefreshBase) {
                operType=2;
                pageIndex++;
                netUrl="https://api.tianapi.com/wxnew/?key=48a7d7193e11bd2dd4a683b6e2f90a4f&num=10&page="+pageIndex;
                requstData();
            }
        });

    }

    private void requstData() {
        //判断网络
       if (NetStateUtil.isConn(this)){
           new Thread(){
               @Override
               public void run() {
                   try {
                       URL url=new URL(netUrl);
                       HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                       urlConnection.setRequestMethod("GET");
                       urlConnection.setConnectTimeout(5000);
                       urlConnection.setReadTimeout(5000);

                       if (urlConnection.getResponseCode()==200){
                           InputStream inputStream = urlConnection.getInputStream();
                           String str = StreamToString.streamToString(inputStream);

                           //插入数据库
                           jsonDao.insertData(netUrl,str);

                           List<ResultData.NewslistBean> newslist = asyncJson(str);

                           Message msg = Message.obtain();
                           msg.obj=newslist;
                           handler.sendMessage(msg);

                       }
                   } catch (Exception e) {
                       e.printStackTrace();
                   }
               }
           }.start();;

       }else{
           //无网状态
           Log.d("zzz","---无网状态，查询数据库中的数据---");
           //NetStateUtil.showNoNetWorkDlg(this);
           Toast.makeText(this,"现在没有网络，请稍后重试！",Toast.LENGTH_SHORT).show();
           //根据现在的url查询出相应的json数据
           String s = jsonDao.questData(netUrl);

           //解析，展示
           List<ResultData.NewslistBean> newslistBeans = asyncJson(s);
           showData(newslistBeans);
       }

    }

    public   List<ResultData.NewslistBean> asyncJson(String json){
        Gson gson=new Gson();//json
        ResultData data=gson.fromJson(json, ResultData.class);
        //从对象中获取列表要显示的集体数据
        List<ResultData.NewslistBean> newslist = data.getNewslist();
        return  newslist;
    }
}

适配器

package com.bwie.com.moniyuekao01;

import android.content.Context;
import android.graphics.Bitmap;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.nostra13.universalimageloader.core.DisplayImageOptions;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.assist.ImageScaleType;

import java.util.List;

/**
 * Created by Administrator on 2018/4/3.
 */

class MyAdapter extends BaseAdapter{
    private Context context;
    private List<ResultData.NewslistBean> newslist;
    private DisplayImageOptions options;
    public MyAdapter(Context context, List<ResultData.NewslistBean> newslist) {
        this.context=context;
        this.newslist=newslist;
        options=new DisplayImageOptions.Builder()
                .cacheInMemory(true)//使用内存缓存
                .cacheOnDisk(true)//使用磁盘缓存
                .showImageOnLoading(R.mipmap.ic_launcher_round)//设置正在下载的图片
                .showImageForEmptyUri(R.mipmap.ic_launcher_round)//url为空或请求的资源不存在时
                .showImageOnFail(R.mipmap.ic_launcher_round)//下载失败时显示的图片
                .bitmapConfig(Bitmap.Config.RGB_565)//设置图片色彩模式
                .imageScaleType(ImageScaleType.EXACTLY)//设置图片的缩放模式
                .build();
    }

    @Override
    public int getCount() {
        return newslist.size();
    }

    @Override
    public Object getItem(int i) {
        return newslist.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        ViewHolder holder=null;
        if (view==null){
            view=View.inflate(context,R.layout.item,null);
            holder=new ViewHolder();
            holder.imageView=view.findViewById(R.id.img);
            holder.textView=view.findViewById(R.id.tv);
            view.setTag(holder);
        }else {
            holder= (ViewHolder) view.getTag();
        }
        holder.textView.setText(newslist.get(i).getTitle());
        ImageLoader.getInstance().displayImage(newslist.get(i).getPicUrl(),holder.imageView,options);


        return view;
    }
    class ViewHolder{
        ImageView imageView;
        TextView textView;
    }
}

网络获取的JSON串

package com.bwie.com.moniyuekao01;

import java.util.List;

/**
 * Created by Administrator on 2018/4/3.
 */

public class ResultData {

    /**
     * code : 200
     * msg : success
     * newslist : [{"ctime":"2018-04-03","title":"农业农村部专家建议：猪价年内不存在长期下跌基础","description":"养猪一家人","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904845.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MzAxMTUzMjEzMw==&idx=2&mid=2653001849&sn=375dc65ed31cdc19dc202470608bcfd7"},{"ctime":"2018-04-03","title":"车险没必要全买！划痕、自燃、涉水等都是花冤枉钱","description":"车早茶","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904772.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MzA4MTQxMjQyNA==&idx=4&mid=2650973250&sn=031b76ea141e780f629118fcb6325980"},{"ctime":"2018-04-03","title":"古训：三种忙不能帮，三种饭不能吃，三种钱不能花","description":"美闻参阅","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904970.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MzA3MDM5ODY4Ng==&idx=1&mid=2651359150&sn=6d754d47ece121154b47e6d03d8e364a"},{"ctime":"2018-04-01","title":"你见过凌晨四点的伦敦吗？英国人这样培养孩子的\u201c韧劲\u201d","description":"世界华人周刊","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62819366.static/640","url":"https://mp.weixin.qq.com/s?__biz=MjM5NDU5ODk2MQ==&idx=2&mid=2676936547&sn=6ab0c535241b2a6e201bb55987bb4b6b"},{"ctime":"2018-04-01","title":"登上《Cell》封面的AI医疗影像诊断系统：机器之心专访UCSD张康教授","description":"机器之心","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904354.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MzA3MzI4MjgzMw==&idx=1&mid=2650740213&sn=0c9b2be6c64f87386789238f640cf6f8"},{"ctime":"2018-04-01","title":"准王妃梅根的硬笔字，惊艳老外！这字绝对是临摹的范本啊啊啊|一周看点","description":"沪江英语","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62850217.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MjM5MjAxNTA0MA==&idx=1&mid=2655356945&sn=596b20d094b25c58333574e734cee553"},{"ctime":"2018-04-01","title":"热巴和赵丽颖是怎么穿印花裙的？","description":"世界时装之苑ELLE","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904155.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MTY3OTM1NTY2MQ==&idx=2&mid=2654353046&sn=e88e592b10de65d5f9007a57d4d68d1f"},{"ctime":"2018-04-01","title":"林清玄：活着，让自己高兴；做人，让别人舒服","description":"有书","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904117.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MjM5Nzg0MTQ3OQ==&idx=3&mid=2660641362&sn=f84de056fc7bd5d1a033ddcec1aea4ba"},{"ctime":"2018-04-01","title":"我保证,你原来吃的烤鱼都弱爆了！| 辣烤鲈鱼","description":"詹姆士的厨房","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-28192017.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MzA4NDc2Njc1NA==&idx=3&mid=2653958960&sn=81e09c2a7069ffa065b6ddd12f444078"},{"ctime":"2018-04-01","title":"500个离婚者的忠告：30岁以前别结婚","description":"有书","picUrl":"https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904036.jpg/640","url":"https://mp.weixin.qq.com/s?__biz=MjM5Nzg0MTQ3OQ==&idx=7&mid=2660641362&sn=937f4fd6ba2a067173b90fbc4fed028e"}]
     */

    private int code;
    private String msg;
    private List<NewslistBean> newslist;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public List<NewslistBean> getNewslist() {
        return newslist;
    }

    public void setNewslist(List<NewslistBean> newslist) {
        this.newslist = newslist;
    }

    public static class NewslistBean {
        /**
         * ctime : 2018-04-03
         * title : 农业农村部专家建议：猪价年内不存在长期下跌基础
         * description : 养猪一家人
         * picUrl : https://zxpic.gtimg.com/infonew/0/wechat_pics_-62904845.jpg/640
         * url : https://mp.weixin.qq.com/s?__biz=MzAxMTUzMjEzMw==&idx=2&mid=2653001849&sn=375dc65ed31cdc19dc202470608bcfd7
         */

        private String ctime;
        private String title;
        private String description;
        private String picUrl;
        private String url;

        public String getCtime() {
            return ctime;
        }

        public void setCtime(String ctime) {
            this.ctime = ctime;
        }

        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        public String getDescription() {
            return description;
        }

        public void setDescription(String description) {
            this.description = description;
        }

        public String getPicUrl() {
            return picUrl;
        }

        public void setPicUrl(String picUrl) {
            this.picUrl = picUrl;
        }

        public String getUrl() {
            return url;
        }

        public void setUrl(String url) {
            this.url = url;
        }
    }
}

工具类

网络判断工具类

package com.bwie.com.moniyuekao01.utiles;

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;

import com.bwie.com.moniyuekao01.R;


/**
 * 得到网络状态的工具类
 * Created by e531 on 2017/10/16.
 */
public class NetStateUtil {

    /*
 * 判断网络连接是否已开
 * true 已打开  false 未打开
 * */
    public static boolean isConn(Context context){
        boolean bisConnFlag=false;
        ConnectivityManager conManager = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo network = conManager.getActiveNetworkInfo();
        if(network!=null){
            bisConnFlag=network.isAvailable();
        }
        return bisConnFlag;
    }

    /**
     * 当判断当前手机没有网络时选择是否打开网络设置
     * @param context
     */
    public static void showNoNetWorkDlg(final Context context) {
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setIcon(R.mipmap.ic_launcher)         //
                .setTitle(R.string.app_name)            //
                .setMessage("当前无网络").setPositiveButton("设置", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // 跳转到系统的网络设置界面
                Intent intent = null;
                // 先判断当前系统版本
                if(android.os.Build.VERSION.SDK_INT > 10){  // 3.0以上
                    intent = new Intent(android.provider.Settings.ACTION_WIRELESS_SETTINGS);
                }else{
                    intent = new Intent();
                    intent.setClassName("com.android.settings", "com.android.settings.WirelessSettings");
                }
                context.startActivity(intent);

            }
        }).setNegativeButton("知道了", null).show();
    }
}

ImageLoader全局适配工具类

package com.bwie.com.moniyuekao01.utiles;

import android.app.Application;
import android.os.Environment;
import android.util.Log;
import android.widget.Toast;

import com.nostra13.universalimageloader.cache.disc.impl.UnlimitedDiscCache;
import com.nostra13.universalimageloader.cache.disc.naming.Md5FileNameGenerator;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;

import java.io.File;

/**
 * Created by Administrator on 2018/4/2.
 */

public class MyApp extends Application{
    @Override
    public void onCreate() {
        super.onCreate();

        Log.d("zzz","App入口");
        Toast.makeText(this,"app", Toast.LENGTH_SHORT).show();

        //自定义sd卡缓存目录 1.android默认cache-app被卸载时，缓存的目录一并被删除    2.自定义
//        File cachefile=getExternalCacheDir();
        File cachefile= new File(Environment.getExternalStorageDirectory().getPath()+"/images");
        //1.初使化--进行一下全局配置 Application
        ImageLoaderConfiguration configuration=new ImageLoaderConfiguration.Builder(this)
                .memoryCacheExtraOptions(400, 700)//缓存图片最大的长和宽
                .threadPoolSize(3)//线程池的数量
                .threadPriority(4)
                .memoryCacheSize(20*1024*1024)//设置内存缓存区大小
                .diskCacheSize(80*1024*1024)//设置sd卡缓存区大小
                .diskCache(new UnlimitedDiscCache(cachefile))//自定义sd卡缓存目录
                .writeDebugLogs()//打印日志内容
                .diskCacheFileNameGenerator(new Md5FileNameGenerator())//给缓存的文件名进行md5加密处理
                .build();
        ImageLoader.getInstance().init(configuration);
    }
}

数据流转换成字符串工具类

package com.bwie.com.moniyuekao01.utiles;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Created by Administrator on 2018/4/2.
 */

public class StreamToString {
    public static String streamToString(InputStream inputStream){
        ByteArrayOutputStream outputStream=null;
        try {
            outputStream = new ByteArrayOutputStream();
            byte[] b=new byte[1024];
            int len;
            while ((len=inputStream.read(b))!=-1){
                outputStream.write(b,0,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return outputStream.toString();
    }

}