Java InputStream在循环上崩溃
出于某种原因,每当我试图将数据库从我的资产文件夹复制到模拟器或某些手机(适用于大多数手机)上的数据库目录时,我都会崩溃。我已经把范围缩小到这段代码Java InputStream在循环上崩溃,java,android,inputstream,outputstream,Java,Android,Inputstream,Outputstream,出于某种原因,每当我试图将数据库从我的资产文件夹复制到模拟器或某些手机(适用于大多数手机)上的数据库目录时,我都会崩溃。我已经把范围缩小到这段代码 //Open your local db as the input stream InputStream myInput = myContext.getAssets().open(DB_NAME); // Path to the just created empty db String outFileName
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
以下是helper类的全部代码
public class NewDbHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.bv.studyguide/databases/";
private static String DB_NAME = "studyguide.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
private static int DB_VERSION = 2;
private SQLiteDatabase db;
private Cursor cursor;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public NewDbHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if (dbExist) {
Log.v("DB Exists", "db exists");
// By calling this method here onUpgrade will be called on a
// writeable database, but only if the version number has been
// bumped
this.getWritableDatabase();
}
dbExist = checkDataBase();
if (!dbExist) {
// By calling this method and empty database will be created into
// the default system path of your application so we are gonna be
// able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE android_metadata (locale TEXT)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (newVersion > oldVersion)
Log.v("Database Upgrade","Database version higher than old.");
myContext.deleteDatabase(DB_NAME);
}
代码在到达实际while循环之前运行良好。根本不进入循环,只是在while行上崩溃并出现IO异常。我不知道这意味着什么,我不太熟悉InputStream和OutputStream,所以我不知道问题可能是什么。在我的Droid X和Droid 2上可以正常工作,但在Droid 1或LG670上不行。有人有什么想法吗
这里是堆栈跟踪:
java.lang.Error: Error copying database
at com.bv.studyguide.NewDbHelper.createDataBase(NewDbHelper.java:63)
at com.bv.studyguide.ArmyStudyGuide.onCreate(ArmyStudyGuide.java:39)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
at android.app.ActivityThread.access$2300(ActivityThread.java:125)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:893)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:651)
at dalvik.system.NativeStart.main(Native Method)
更新:
我也遇到了一个问题,与另一个应用程序相同的代码(实际上)。但复制数据库时不会出现异常。它复制整个数据库,但随后决定不在数据库中放入任何内容。因此它读取3072字节,但其中唯一的表是android_元数据表。我真的很困惑。这个字节数组是问题的根源吗?我找到了问题所在。在Gingerbread之前,Android不允许您访问资产文件夹中大于1GB的文件。因此,我只是将这些文件分段,并制作了一个方法,在运行时循环遍历这些文件并将htem放回一起。请包括异常。请提供异常详细信息。myInput可能会有一些问题,但如果附加异常“崩溃…带有IO异常。我不知道这意味着什么”,则会更清楚。我们也不知道这意味着什么,除非您发布异常,否则我们永远不会知道。您应该始终链接您的异常:
抛出新错误(“复制数据库时出错”,e)代码>因此您可以看到IOException
实际上是什么。我怀疑这是权限问题。它显然是在onCreate
中调用的。不幸的是,异常处理会从堆栈跟踪中删除任何有用的信息。不要只抛出新错误()
,或者重新抛出IOE,或者将其链接到错误
。