Java 8 moving forward with functional programming... And how Scala copes with it.

• http://readwrite.com/2014/02/20/java-8-scala-competitors-bff...

Robochecker published on Google Code

We are proud to announce that the whole source code and documentation about our "lego robot playing draughts" is on Google Code, exactly here.

The software has been written in Java, using leJOS API for controlling the NXT Brick.
It is possible to use Java by flashing a custom firmware on it.

It has been a great chance to improve our programming knowledge in Java (in source code you'll find a lot of code as implementation of threading, class factories, interfaces) and have fun.

Android Developers. Thread Opened.

I choose to open a thread regarding Sun JavaMail, JAF and Android.
I hope it would be useful for all developers whose encountered issues or difficulties using JavaMail on Android.
There were few troubles:

• java.awt.Datatransfer class was missing (and related interfaces): they are available in the Apache Harmony SVN. There were some java.awt.Image dependancies, which have been removed.
  
• The lastest Sun JavaMail API was not working on Android: at build time, the APK popped up an error within an IMAP class. I downloaded source code of it (now Sun JM is opensource) and I fixed some classes.
• Sun JavaMail was working, but not at 100%: it was unable to manage Multipart elements of an email (so most of the email we receive). This API stored MIME-Types to/from Java Object association (a sort of mapping between them) in 2 files within the JAR file. Android is unable to read files in the classic way (due to security policy), so I decided to add the "MIME mapping" programmatically.

You can find the post on Android Developers here.

Android Developers Google Group - A focus on ContentProvider

As requested here, I'm posting some example code for implementing a ContentProvider on which is possible to call openOutputStream and openInputStream.
My only question is: why must I store file path in a database field called '_data', if openFile implementation is programmer's burden?

ElementProvider.java

/*
 Copyright (C) 2008  Luca Belluccini

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program.  If not, see .
*/

package polito.mailandroid;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashMap;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.net.Uri;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.os.ParcelFileDescriptor;
import android.text.TextUtils;

public class ElementProvider extends ContentProvider {
private static final String DATABASE_NAME = "poli";
private static final String DATABASE_TABLE = "elements";
private static final int DATABASE_VERSION = 1;
public static final String KEY_ID = "_id";
public static final String KEY_DATA = "_data";
public static final String KEY_MIMETYPE = "mimetype";

private DatabaseHelper mDbH;

 private static class DatabaseHelper extends SQLiteOpenHelper {
     DatabaseHelper(Context context) {
         super(context, DATABASE_NAME, null, DATABASE_VERSION);
     }
  
 public void onOpen(SQLiteDatabase db) {
  super.onOpen(db);
 }

 public void onCreate(SQLiteDatabase db) {
         db.execSQL("create table " + DATABASE_TABLE + " (" +
           KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
           KEY_MIMETYPE + " TEXT, " +
           KEY_DATA + " TEXT" +
           " );");
     }
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
         db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
         onCreate(db);
     }
 }



public static final int ELEMENTS = 1;
public static final int ELEMENT_ID = 2;
public static final Uri CONTENT_URI = Uri.parse("content://polito.mailandroid/elements");
private static final UriMatcher URI_MATCHER;
private static HashMap ELEMENTS_LIST_PROJECTION_MAP;
 static {
     URI_MATCHER = new UriMatcher(UriMatcher.NO_MATCH);
     URI_MATCHER.addURI("polito.mailandroid", "elements", ELEMENTS);
     URI_MATCHER.addURI("polito.mailandroid", "elements/#", ELEMENT_ID);

     ELEMENTS_LIST_PROJECTION_MAP = new HashMap();
     ELEMENTS_LIST_PROJECTION_MAP.put(KEY_ID, KEY_ID);
     ELEMENTS_LIST_PROJECTION_MAP.put(KEY_DATA, KEY_DATA);
     ELEMENTS_LIST_PROJECTION_MAP.put(KEY_MIMETYPE, KEY_MIMETYPE);
 }

public boolean onCreate() {
     mDbH = new DatabaseHelper(getContext());
     return true;
}

public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
 String[] projection = new String[] {
     ElementProvider.KEY_DATA
 };
 Cursor c = query(uri,projection,null,null,null);
 c.moveToFirst();
 String file = c.getString(c.getColumnIndexOrThrow(ElementProvider.KEY_DATA));
 c.close();
 File f = new File(file);
 int m = ParcelFileDescriptor.MODE_READ_ONLY;
 if (mode.equalsIgnoreCase("rw"))
  m = ParcelFileDescriptor.MODE_READ_WRITE;
 ParcelFileDescriptor pfd = ParcelFileDescriptor.open(f,m);
 return pfd;
 }

public Uri insert(Uri uri, ContentValues initialValues) {
     if (URI_MATCHER.match(uri) != ELEMENTS) {
      // !!!
     }
     ContentValues values;
     if (initialValues != null) {
         values = new ContentValues(initialValues);
     } else {
         values = new ContentValues();
     }
  
     if (!values.containsKey(KEY_MIMETYPE))
      values.put(KEY_MIMETYPE, "plain/text");

     SQLiteDatabase mDb = mDbH.getWritableDatabase();
     long rowID = mDb.insert(DATABASE_TABLE, "notnull", values);
     if (rowID > 0) {
         if (!values.containsKey(KEY_DATA)){
            try {
             String filename = rowID + "";
       getContext().openFileOutput(filename, Context.MODE_PRIVATE).close();
       String path = getContext().getFileStreamPath(filename).getAbsolutePath();
       values.put(KEY_DATA, path);
       update(uri,values,KEY_ID + "=" + rowID, null);
      } catch (Exception e) {
       // !!!
      }
         }
         Uri newUri = ContentUris.withAppendedId(ElementProvider.CONTENT_URI, rowID);
         getContext().getContentResolver().notifyChange(newUri, null);
         return newUri;
     }
     // !!!
     return null;
 }

public Cursor query(Uri uri, String[] projection, String selection,
         String[] selectionArgs, String sortOrder) {
     SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
     switch (URI_MATCHER.match(uri)) {
        case ELEMENTS:
            qb.setTables(DATABASE_TABLE);
            qb.setProjectionMap(ELEMENTS_LIST_PROJECTION_MAP);
            break;
        case ELEMENT_ID:
            qb.setTables(DATABASE_TABLE);
            qb.appendWhere(KEY_ID + "=" + uri.getPathSegments().get(1));
            break;
        default:
            throw new IllegalArgumentException("Unknown URL " + uri);
     }
     SQLiteDatabase mDb = mDbH.getReadableDatabase();
     Cursor c = qb.query(mDb, projection, selection, selectionArgs, null, null, "_id DESC");
     c.setNotificationUri(getContext().getContentResolver(), uri);
     return c;
 }

public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
     int code = URI_MATCHER.match(uri);
     int count = 0;
     SQLiteDatabase mDb = mDbH.getWritableDatabase();
     switch (code) {
      case ELEMENTS:
            count = mDb.update(DATABASE_TABLE, values, selection, selectionArgs);
            break;
        case ELEMENT_ID:
            String id = uri.getPathSegments().get(1);
            count =
                    mDb.update(DATABASE_TABLE, values, KEY_ID + "=" + id
                            + (!TextUtils.isEmpty(selection) ? " AND ("
                                    + selection + ')' : ""), selectionArgs);
            break;
        default:
            throw new IllegalArgumentException("Unknown URL " + uri);
     }
     getContext().getContentResolver().notifyChange(uri, null);
     return count;
}

public int delete(Uri uri, String where, String[] whereArgs) {
     int code = URI_MATCHER.match(uri);
     int count = 0;
     SQLiteDatabase mDb = mDbH.getWritableDatabase();
     switch (code) {
        case ELEMENTS:
         // !!! REMOVE ALL FILES
            count = mDb.delete(DATABASE_TABLE, where, whereArgs);
            break;
        case ELEMENT_ID:
            String id = uri.getPathSegments().get(1);
            // !!! REMOVE ASSOCIATED FILE
            count =
                    mDb.delete(DATABASE_TABLE, KEY_ID + "=" + id
                            + (!TextUtils.isEmpty(where) ? " AND (" + where
                                    + ')' : ""), whereArgs);
            break;
        default:
            // !!!
     }
     getContext().getContentResolver().notifyChange(uri, null);
     return count;
}

public String getType(Uri uri) {
 String[] projection = new String[] {
     ElementProvider.KEY_MIMETYPE
 };
 Cursor c = query(uri,projection,null,null,null);
 c.moveToFirst();
 String mimetype = c.getString(c.getColumnIndexOrThrow(ElementProvider.KEY_MIMETYPE));
 c.close();
     return mimetype;
}

}

Mail Android updated

In this screenshot is shown the content of a POP3 Folder. Notice that only Subject and From field were fetched from the entire message (less data to transfer).

Android

I'll write my monograph for deegree about Android!

Exactly, I will develop a mail client.

=)