Android编程权威指南-第十七章挑战练习

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CriminalIntentJSONSerializer.java文件

package com.onevol.app;import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.OutputStreamWriter;import java.io.Writer;import java.util.ArrayList;import org.json.JSONArray;import org.json.JSONException;import org.json.JSONTokener;import android.content.Context;import android.os.Environment;public class CriminalIntentJSONSerializer {    private Context mContext;    private String mFilename;    public CriminalIntentJSONSerializer(Context c, String f){        mContext = c;        mFilename = f;    }    public void saveCrimes(ArrayList<Crime> crimes) throws JSONException, IOException{        JSONArray array = new JSONArray();        for(Crime c : crimes)            array.put(c.toJSON());        Writer writer = null;        try{            OutputStream out = null;            if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){//检测是否有sd卡                File sdCard = new File(Environment.getExternalStorageDirectory().getAbsolutePath(), mFilename);//获取sd卡的绝对路径，就是全部的路径。                out = new FileOutputStream(sdCard);            }else{                out = mContext.openFileOutput(mFilename, Context.MODE_PRIVATE);            }            writer = new OutputStreamWriter(out);            writer.write(array.toString());        } finally {            if(writer != null)                writer.close();        }    }    public ArrayList<Crime> loadCrimes() throws IOException, JSONException{        ArrayList<Crime> crimes = new ArrayList<Crime>();        BufferedReader reader = null;        try{            InputStream in = null;            if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){                File sdCard = new File(Environment.getExternalStorageDirectory().getAbsolutePath(), mFilename);                in = new FileInputStream(sdCard);            }else{                in = mContext.openFileInput(mFilename);            }            reader = new BufferedReader(new InputStreamReader(in));            StringBuilder jsonString = new StringBuilder();            String line = null;            while((line = reader.readLine()) != null){                jsonString.append(line);            }            JSONArray array = (JSONArray) new JSONTokener(jsonString.toString()).nextValue();            for(int i = 0; i < array.length(); i++){                crimes.add(new Crime(array.getJSONObject(i)));            }         }catch(FileNotFoundException e){            }finally{                if(reader != null)                    reader.close();            }        return crimes;    }}

并在AndroidManifest.xml文件中声明权限

<uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

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