Android离线缓存

Posted 2020-08-28

android做到一定程度，需要考虑缓存的问题，不信可以掏出手机看看淘宝等一些app是否无网的情况下还可以浏览，不过大部分app并没有考虑到这些问题，解决Android的缓存有哪些方法呢

1.IO流读写文件

2.数据库

3.LruCache和DiskLruCache

个人比较喜欢sd卡文件读写的方式，原因自己可以去分析。

（1）权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"></uses-permission>
<!-- 在SDCard中创建与删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 往SDCard写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
（2）判断网络连接的状态，有什么用呢？自己想

if (isNetworkAvailable(MainActivity.this)) {
    Toast.makeText(getApplicationContext(), "当前有可用网络！", Toast.LENGTH_LONG).show();

} else {
    Toast.makeText(getApplicationContext(), "当前wu可用网络！", Toast.LENGTH_LONG).show();
}

public boolean isNetworkAvailable(Activity activity)
{
    Context context = activity.getApplicationContext();
    // 获取手机所有连接管理对象（包括对wi-fi,net等连接的管理）
    ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);

    if (connectivityManager == null)
    {
        return false;
    }
    else
    {
        // 获取NetworkInfo对象
        NetworkInfo[] networkInfo = connectivityManager.getAllNetworkInfo();

        if (networkInfo != null && networkInfo.length > 0)
        {
            for (int i = 0; i < networkInfo.length; i++)
            {
                System.out.println(i + "===状态===" + networkInfo[i].getState());
                System.out.println(i + "===类型===" + networkInfo[i].getTypeName());
                // 判断当前网络状态是否为连接状态
                if (networkInfo[i].getState() == NetworkInfo.State.CONNECTED)
                {
                    return true;
                }
            }
        }
    }
    return false;
}

（3）端口写入数据

    if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
    File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录
    File saveFile = new File(sdCardDir, "itcast.txt");
    FileOutputStream outStream = new FileOutputStream(saveFile);
    outStream.write(result.getBytes());
    outStream.close();
}
（4）读取数据

File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录
File saveFile1   = new File(sdCardDir, "itcast.txt");
BufferedReader br = null;
try {
    br = new BufferedReader(new FileReader(saveFile1));
    String readline = "";
    StringBuffer sb = new StringBuffer();
    while ((readline = br.readLine()) != null) {
        System.out.println("readline:" + readline);
        sb.append(readline);
    }
    String str = sb.toString();
(5)部分完整demo1

if (isNetworkAvailable(MainActivity.this)) {
    Toast.makeText(getApplicationContext(), "当前有可用网络！", Toast.LENGTH_LONG).show();

} else {
    Toast.makeText(getApplicationContext(), "当前wu可用网络！", Toast.LENGTH_LONG).show();
    File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录
    File saveFile1   = new File(sdCardDir, "itcast.txt");
    BufferedReader br = null;
    try {
        br = new BufferedReader(new FileReader(saveFile1));
        String readline = "";
        StringBuffer sb = new StringBuffer();
        while ((readline = br.readLine()) != null) {
            System.out.println("readline:" + readline);
            sb.append(readline);
        }
        String str = sb.toString();
        JSONObject jsonObject = new JSONObject(str);
        JSONArray jsonArray = jsonObject.getJSONArray("data");
        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject object = jsonArray.getJSONObject(i);
            String title = object.getString("name");
            String content = object.getString("description");
            String url = object.getString("picSmall");
            domainBean newsInfo = new domainBean(title, content, url);

            //String path = Environment.getExternalStorageDirectory() + "/" +  name;
            //ObjectOutputStream out =new ObjectOutputStream(new FileOutputStream(path));
            //out.writeObject(newsInfo);
            list.add(newsInfo);
            //新建适配器
            beanAdapter = new BeanAdapter(list, MainActivity.this);
            //配置适配器
            xListView.setAdapter(beanAdapter);
            br.close();

        }

    } catch (IOException e) {
        e.printStackTrace();
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

(6)部分完整demo2

 public String logoutPost(String URL){
        String result = "";
        try {
            String data = URLEncoder.encode("UTF-8");
// + "&password=" + URLEncoder.encode(password, "UTF-8");//传递的数据
            URL url = new URL(URL);
//2、url.openConnection()打开网络链接
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//3、设置请求的方式
            conn.setRequestMethod("POST");
            conn.setDoInput(true);//发送POST请求必须设置允许输出
            conn.setDoOutput(true);//发送POST请求必须设置允许输入
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            conn.setRequestProperty("Charset", "utf-8");
            conn.setRequestProperty("Content-Length", String.valueOf(data.getBytes().length));
//5、获取输出流
            OutputStream os = conn.getOutputStream();
            os.write(data.getBytes());
            os.flush();
            BufferedReader in=new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while((line=in.readLine())!=null){result+="\n"+line;}
                        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录
                File saveFile = new File(sdCardDir, "itcast.txt");
                FileOutputStream outStream = new FileOutputStream(saveFile);
                outStream.write(result.getBytes());
                outStream.close();
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }