优先存储SDCard ，无sdcard存在手机内存中！

思路：重写SQLiteOpenHelper  getWritableDatabase和getReadableDatabase方法，子类继承实现
package com.c35.mtd.oa.database;
import java.io.File;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.util.Log;
/**
 * @title: 移动OA
 * @description: sdcard数据库操作类
 * @company: 三五互联
 * @author sunny
 * @version 1.0
 * @created on 2011-4-12
 */
public abstract class SQLiteOpenHelper { private static final String TAG = "SDSQLiteOpenHelper";
 private final Context mContext;
 private final String mName;
 private final CursorFactory mFactory;
 private final int mNewVersion;
 private SQLiteDatabase mDatabase = null;
 private boolean mIsInitializing = false;
 public SQLiteOpenHelper(Context context, String name,
   CursorFactory factory, int version) {  if (version < 1)
   throw new IllegalArgumentException("Version must be >= 1, was "
     + version);  mContext = context;
  mName = name;
  mFactory = factory;
  mNewVersion = version;
 }
 public synchronized SQLiteDatabase getWritableDatabase() {
  if (mDatabase != null && mDatabase.isOpen() && !mDatabase.isReadOnly()) {
   return mDatabase; // The database is already open for business
  }
  if (mIsInitializing) {
   throw new IllegalStateException(
     "getWritableDatabase called recursively");  }
  // If we have a read-only database open, someone could be using it
  // (though they shouldn't), which would cause a lock to be held on
  // the file, and our attempts to open the database read-write would
  // fail waiting for the file lock. To prevent that, we acquire the
  // lock on the read-only database, which shuts out other users.
  boolean success = false;
  SQLiteDatabase db = null;
  try {
   mIsInitializing = true;
   if (mName == null) {
    db = SQLiteDatabase.create(null);
   } else {
    if(SDCardUtils.isSdCard()){//获得SDCard 数据库
     String path = getDatabasePath(mName).getPath();
     db = SQLiteDatabase.openOrCreateDatabase(path, mFactory);
     Log.i("sunny", "create database in sdcard");
    }else{//获得手机数据库
     db = mContext.openOrCreateDatabase(mName, 0, mFactory);
    }
   }   int version = db.getVersion();
   if (version != mNewVersion) {
    db.beginTransaction();
    try {
     if (version == 0) {
      onCreate(db);
     } else {
      onUpgrade(db, version, mNewVersion);
     }
     db.setVersion(mNewVersion);
     db.setTransactionSuccessful();
    } finally {
     db.endTransaction();
    }
   }
   onOpen(db);
   success = true;
   return db;
  } finally {
   mIsInitializing = false;
   if (success) {
    if (mDatabase != null) {
     try {
      mDatabase.close();
     } catch (Exception e) {
     }    }
    mDatabase = db;
   } else {
    if (db != null)
     db.close();   }
  }
 }
 public synchronized SQLiteDatabase getReadableDatabase() {
  if (mDatabase != null && mDatabase.isOpen()) {
   return mDatabase; // The database is already open for business
  }
  if (mIsInitializing) {
   throw new IllegalStateException(
     "getReadableDatabase called recursively");  }
  try {
   return getWritableDatabase();
  } catch (SQLiteException e) {
   if (mName == null)
    throw e; // Can't open a temp database read-only!   Log.e(TAG, "Couldn't open " + mName
     + " for writing (will try read-only):", e);  }
  SQLiteDatabase db = null;
  try {
   mIsInitializing = true;
   String path = "";
   if(SDCardUtils.isSdCard()){//获得SDCard 数据库
    path = mContext.getDatabasePath(mName).getPath();
    db = SQLiteDatabase.openOrCreateDatabase(path, mFactory);
   }else{
    path = getDatabasePath(mName).getPath();
    db = SQLiteDatabase.openDatabase(path, mFactory,
      SQLiteDatabase.OPEN_READWRITE);
   }
      if (db.getVersion() != mNewVersion) {
    throw new SQLiteException(
      "Can't upgrade read-only database from version " +      db.getVersion() + " to " + mNewVersion + ": " + path);
   }
   onOpen(db);
   Log.w(TAG, "Opened " + mName + " in read-only mode");
   mDatabase = db;
   return mDatabase;
  } finally {
   mIsInitializing = false;
   if (db != null && db != mDatabase)
    db.close();  }
 }
 public synchronized void close() {
  if (mIsInitializing)
   throw new IllegalStateException("Closed during initialization");
  if (mDatabase != null && mDatabase.isOpen()) {
   mDatabase.close();
   mDatabase = null;
  }
 } public File getDatabasePath(String name) {
  return new File("/sdcard/" + name);
 } public abstract void onCreate(SQLiteDatabase db);
 public abstract void onUpgrade(SQLiteDatabase db, int oldVersion,
   int newVersion); public void onOpen(SQLiteDatabase db) {
 }}