Android开发之数据库备份
Android开发之数据库备份
用过市面上刷题App/诸如驾考宝典这样的App/的用户应该知道，离线状态也是可以刷题的，这就表明了题库并不是在服务器或者云端数据库上，而是用本地的SQLite数据库存储的。可是如果别人给你的题库是个Excel表格，让你去开发成个App，该如何去做呢？接下来就以我曾经做过的C语言刷题App为例手把手教你如何读取Excel表格，并备份数据库。
1 自定义实体类
这个就好理解了，咱这回存的是题目，就自定义一个保存题目信息的实体类，具体里面存放什么信息因需求而定。
public class Question {
private int questionId;
private String questionContent;
private String answerA;
private String answerB;
private String answerC;
private String answerD;
private int answerNum;
private String coment;
private String answerE;
private String answerF;
private int answerCorrect;
private int answerChoose;
private int haveFinished;
private int isTrue;
private int chapter;
public Question(){}
public int getQuestionId() {
return questionId;
}
public void setQuestionId(int questionId) {
this.questionId = questionId;
}
public String getQuestionContent() {
return questionContent;
}
public void setQuestionContent(String questionContent) {
this.questionContent = questionContent;
}
public String getAnswerA() {
return answerA;
}
public void setAnswerA(String answerA) {
this.answerA = answerA;
}
public String getAnswerB() {
return answerB;
}
public void setAnswerB(String answerB) {
this.answerB = answerB;
}
public String getAnswerC() {
return answerC;
}
public void setAnswerC(String answerC) {
this.answerC = answerC;
}
public String getAnswerD() {
return answerD;
}
public void setAnswerD(String answerD) {
this.answerD = answerD;
}
public int getAnswerNum() {
return answerNum;
}
public void setAnswerNum(int answerNum) {
this.answerNum = answerNum;
}
public String getComent() {
return coment;
}
public void setComent(String coment) {
this.coment = coment;
}
public String getAnswerE() {
return answerE;
}
public void setAnswerE(String answerE) {
this.answerE = answerE;
}
public String getAnswerF() {
return answerF;
}
public void setAnswerF(String answerF) {
this.answerF = answerF;
}
public int getAnswerCorrect() {
return answerCorrect;
}
public void setAnswerCorrect(int answerCorrect) {
this.answerCorrect = answerCorrect;
}
public int getAnswerChoose() {
return answerChoose;
}
public void setAnswerChoose(int answerChoose) {
this.answerChoose = answerChoose;
}
public int getHaveFinished() {
return haveFinished;
}
public void setHaveFinished(int haveFinished) {
this.haveFinished = haveFinished;
}
public int getIsTrue() {
return isTrue;
}
public void setIsTrue(int isTrue) {
this.isTrue = isTrue;
}
public int getChapter() {
return chapter;
}
public void setChapter(int chapter) {
this.chapter = chapter;
}
}
2 封装对SQLite数据库操作的工具类
public class questionOpenHelper extends SQLiteOpenHelper{
/*
* Sqlite数据库
* 包括数据库的创建、备份
* */
public static final String CREATE_QUESTION="create table Question (" +
"questionId integer primary key autoincrement," +
"questionContent text," +
"answerA text," +
"answerB text," +
"answerC text," +
"answerD text," +
"answerE text," +
"answerF text," +
"coment text," +
"answerCorrect integer," +
"answerChoose integer," +
"answerNum integer," +
"haveFinished integer," +
"isTrue integer," +
"chapter integer)";
private Context context;
public questionOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
this.context=context;
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_QUESTION);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}public class QuestionDB {
private static final String DB_NAME="English";
private static final int VERSION=1;
private static QuestionDB questionDB;
private SQLiteDatabase db;
private QuestionDB(Context context) {
questionOpenHelper helper = new questionOpenHelper(context, DB_NAME, null, VERSION);
db = helper.getWritableDatabase();
}
public synchronized static QuestionDB getInstance(Context context){
if(questionDB==null){
questionDB=new QuestionDB(context);
}
return questionDB;
}
public void saveQuestion(Question question){
if(question!=null){
ContentValues values=new ContentValues();
values.put("questionContent",question.getQuestionContent());
values.put("answerA",question.getAnswerA());
values.put("answerB",question.getAnswerB());
values.put("answerC",question.getAnswerC());
values.put("answerD",question.getAnswerD());
values.put("answerNum",question.getAnswerNum());
values.put("answerE",question.getAnswerE());
values.put("answerF",question.getAnswerF());
values.put("answerChoose",question.getAnswerChoose());
values.put("answerCorrect",question.getAnswerCorrect());
values.put("coment",question.getComent());
values.put("haveFinished",question.getHaveFinished());
values.put("isTrue",question.getIsTrue());
values.put("chapter",question.getChapter());
db.insert("Question", null, values);
}
}
}这种封装数据库的写法是沿袭了《第一行代码》中对于SQLite的封装写法，questionOpenHelper继承SQLiteOpenHelper，完成数据库的生成，QuestionDB写成单例，里面可以写对于数据库的各种操作，本例中只写了对于数据库数据的存储。
3 读取Excel表格，生成原始SQLite数据库 
那tm怎么读取Excel表格呢？
好吧！其实是有解决这个的相应工具类库。
jxl.jar 直接百度搜这个 在CSDN免费下载
然后把 jxl.jar 导入到工程，把Excel表格放在assets文件夹下，如果没这个文件夹就在main文件夹下新建assets文件夹，此处说的是Android studio的相应方法，eclipse肯定是有类似操作的，但是不是和as一样就不晓得了。
准备工作做好了，接下来就是读取Excel表格了，我的做法是写一个辅助Activity去处理这些并不需要让用户使用的功能，也就是说这个Activity也就是在开发时用，在以后开发完成之后不将其写进AndroidManifest中，这个Activity的布局也就很简单 ，线性放几个按钮就行了，反正也不是给用户看的。
public class AssistActivity extends Activity{
/*
* 这个界面并没有用上，只是作为辅助界面用的
* */
private Toast toast;
private Button read_btn;
private QuestionDB questionDB;
private Question question;
private void tips(String str){
toast.setText(str);
toast.show();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.assist_layout);
toast=Toast.makeText(this,"",Toast.LENGTH_SHORT);
read_btn=(Button)findViewById(R.id.read_btn);
questionDB=QuestionDB.getInstance(this);
read_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//读取Excel表格
try {
InputStream mInputStream = getResources().getAssets().open("problem3.xls");
Workbook wb = Workbook.getWorkbook(mInputStream);
Sheet mSheet = wb.getSheet(0);
int row = mSheet.getRows();
Cell temp;
for(int i= 1 ; i < row ; i ++){
question=new Question();
temp = mSheet.getCell(1, i);
question.setQuestionContent(temp.getContents());
question.setAnswerNum(4);
temp=mSheet.getCell(3,i);
question.setAnswerA(temp.getContents());
temp=mSheet.getCell(4,i);
question.setAnswerB(temp.getContents());
temp=mSheet.getCell(5,i);
question.setAnswerC(temp.getContents());
temp=mSheet.getCell(6,i);
question.setAnswerD(temp.getContents());
temp=mSheet.getCell(9,i);
if(temp.getContents().equals("A")){
question.setAnswerCorrect(1);
}else if(temp.getContents().equals("B")){
question.setAnswerCorrect(2);
}else if(temp.getContents().equals("C")){
question.setAnswerCorrect(3);
}else if(temp.getContents().equals("D")){
question.setAnswerCorrect(4);
}
temp=mSheet.getCell(10,i);
question.setComent(temp.getContents());
temp=mSheet.getCell(11,i);
int cha;
try {
cha = Integer.parseInt(temp.getContents());
}catch (Exception e){
cha=9;
}
question.setChapter(cha-1);
question.setIsTrue(0);
question.setHaveFinished(0);
questionDB.saveQuestion(question);
}
wb.close();
mInputStream.close();
} catch (BiffException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IndexOutOfBoundsException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
布局文件就不贴出来了，简单的不能再简单的就是一个按钮 按一下 ，然后就开始从Excel中读取信息，生成初试SQLite数据库，其实我这块代码写的还是挺有问题的，因为读取操作和存储操作都是耗时操作，点击按钮 的时候可以明显感到手机卡顿了好几秒，其实这里开辟一个子线程去处理更加合适一点，不过毕竟不是给用户用的，所以只要没ANR也就无所谓了。
4 备份SQLite数据库
其实这之前大段大段的都是怎么通过Excel生成初始的SQLite数据库，既然生成了初始数据库，就把它备份下来。
依然是在上一步中的辅助Activity中，加一个按钮，然后把下面这段代码写在按钮的触发操作中
file_btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
File dbFile = getDatabasePath("English");
File file = new File(Environment.getExternalStorageDirectory(), "English");
if (!file.exists()) {
try {
file.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
}
FileInputStream is = new FileInputStream(dbFile);
FileOutputStream out = new FileOutputStream(file);
byte[] buff = new byte[1024];
int n = 0;
while ((n = is.read(buff)) > 0) {
Log.e("tag", "len=" + n);
out.write(buff, 0, n);
}
is.close();
out.close();
}catch (Exception e){}
}
});这段代码就是在sd卡中生成一个名为English的File，然后把数据库中的信息通过流导入到File中，这样先点击read_btn，生成SQLite数据库，再点击file_btn，在sd卡中生成file，这里因为涉及到了对于sd卡的操作，得在AndroidMainfests中写入相应的权限。在手机的sd卡中找到名叫English的File，把File传给电脑，然后依然是把这个File放在assets目录下，数据库的备份到这算结束了。
5 修改数据库工具类，实现第一次打开App时，导入已经初始化的SQLite数据库信息
public class questionOpenHelper extends SQLiteOpenHelper{
/*
* Sqlite数据库
* 包括数据库的创建、备份
* */
private static String DB_PATH = "/data/data/com.example.cjm.englishlearn/databases/";
private static final String DB_NAME="English";
public static final String CREATE_QUESTION="create table Question (" +
"questionId integer primary key autoincrement," +
"questionContent text," +
"answerA text," +
"answerB text," +
"answerC text," +
"answerD text," +
"answerE text," +
"answerF text," +
"coment text," +
"answerCorrect integer," +
"answerChoose integer," +
"answerNum integer," +
"haveFinished integer," +
"isTrue integer," +
"chapter integer)";
private Context context;
public questionOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
this.context=context;
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_QUESTION);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if(dbExist){
return;
}else{
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
private void copyDataBase() throws IOException {
InputStream myInput = context.getAssets().open(DB_NAME);
String outFileName = DB_PATH + DB_NAME;
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
}
public class QuestionDB {
private static final String DB_NAME="English";
private static final int VERSION=1;
private static QuestionDB questionDB;
private SQLiteDatabase db;
private QuestionDB(Context context) {
questionOpenHelper helper = new questionOpenHelper(context, DB_NAME, null, VERSION);
try {
helper.createDataBase();
} catch (IOException e) {}
db = helper.getWritableDatabase();
}
/*省略n行代码*/
}当调用QuestionDB时，会先通过checkDataBase()检测是否已经生成了SQLite数据库，如果没生成，即App是第一次打开，通过流从存放在assets目录下的English导入到新生成的SQLite中，实现数据库的初始化。
尾记：
因为最早App是打算做成英语单选的刷题App，所以中间好多东西的起名字都用了English，其实这跟英语基本上没半毛钱关系，自行忽略就好。