Android编程权威指南-第十七章挑战练习

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 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 loadCrimes() throws IOException, JSONException{
        ArrayList crimes = new ArrayList();
        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"/>