android中使用sqlite、复制assets下的数据库到SD卡、支持大于1M的文件

初学android，达人忽略，欢迎扔石头.

android中使用sqlite、复制assets下的数据库到SD卡、支持大于1M的文件

如果使用SD卡，需要在AndroidManifest.xml中设置权限

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--><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"></uses-permission>

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-->  1 package cn.arthur.common;
  2 
  3 import java.io.File;
  4 import java.io.FileOutputStream;
  5 import java.io.IOException;
  6 import java.io.InputStream;
  7 import java.io.OutputStream;
  8 
  9 import android.content.Context;
 10 import android.database.sqlite.SQLiteDatabase;
 11 import android.database.sqlite.SQLiteDatabase.CursorFactory;
 12 import android.database.sqlite.SQLiteException;
 13 import android.database.sqlite.SQLiteOpenHelper;
 14 
 15 /**
 16  * @author Joshua
 17  * 用法：
 18  * DBHelper dbHelper = new DBHelper(this);
 19  * dbHelper.createDataBase();
 20  * SQLiteDatabase db = dbHelper.getWritableDatabase();
 21  * Cursor cursor = db.query()
 22  * db.execSQL(sqlString);
 23  * 注意：execSQL不支持带;的多条SQL语句，只能一条一条的执行，晕了很久才明白
 24  * 见execSQL的源码注释 (Multiple statements separated by ;s are not supported.)
 25  * 将把assets下的数据库文件直接复制到DB_PATH，但数据库文件大小限制在1M以下
 26  * 如果有超过1M的大文件，则需要先分割为N个小文件，然后使用copyBigDatabase()替换copyDatabase()
 27  */
 28 public class DBHelper extends SQLiteOpenHelper {
 29     //用户数据库文件的版本
 30     private static final int DB_VERSION    = 1;
 31     //数据库文件目标存放路径为系统默认位置，cn.arthur.examples 是你的包名
 32     private static String DB_PATH        = "/data/data/cn.arthur.examples/databases/";
 33 /*
 34     //如果你想把数据库文件存放在SD卡的话
 35     private static String DB_PATH        = android.os.Environment.getExternalStorageDirectory().getAbsolutePath()
 36                                         + "/arthurcn/drivertest/packfiles/";
 37 */
 38     private static String DB_NAME         = "hello.db";
 39     private static String ASSETS_NAME     = "hello.db";
 40 
 41     private SQLiteDatabase myDataBase    = null;
 42     private final Context myContext;
 43 
 44      /** 
 45       * 如果数据库文件较大，使用FileSplit分割为小于1M的小文件
 46       * 此例中分割为 hello.db.101    hello.db.102    hello.db.103
 47       */
 48     //第一个文件名后缀
 49     private static final int ASSETS_SUFFIX_BEGIN    = 101;
 50     //最后一个文件名后缀
 51     private static final int ASSETS_SUFFIX_END        = 103;
 52     
 53     /**
 54      * 在SQLiteOpenHelper的子类当中，必须有该构造函数
 55      * @param context    上下文对象
 56      * @param name        数据库名称
 57      * @param factory    一般都是null
 58      * @param version    当前数据库的版本，值必须是整数并且是递增的状态
 59      */
 60     public DBHelper(Context context, String name, CursorFactory factory, int version) {
 61         //必须通过super调用父类当中的构造函数
 62         super(context, name, null, version);
 63         this.myContext = context;
 64     }
 65     
 66     public DBHelper(Context context, String name, int version){
 67         this(context,name,null,version);
 68     }
 69 
 70     public DBHelper(Context context, String name){
 71         this(context,name,DB_VERSION);
 72     }
 73     
 74     public DBHelper (Context context) {
 75         this(context, DB_PATH + DB_NAME);
 76     }
 77     
 78     public void createDataBase() throws IOException{
 79         boolean dbExist = checkDataBase();
 80         if(dbExist){
 81             //数据库已存在，do nothing.
 82         }else{
 83             //创建数据库
 84             try {
 85                 File dir = new File(DB_PATH);
 86                 if(!dir.exists()){
 87                     dir.mkdirs();
 88                 }
 89                 File dbf = new File(DB_PATH + DB_NAME);
 90                 if(dbf.exists()){
 91                     dbf.delete();
 92                 }
 93                 SQLiteDatabase.openOrCreateDatabase(dbf, null);
 94                 // 复制asseets中的db文件到DB_PATH下
 95                 copyDataBase();
 96             } catch (IOException e) {
 97                 throw new Error("数据库创建失败");
 98             }
 99         }
100     }
101     
102     //检查数据库是否有效
103     private boolean checkDataBase(){
104         SQLiteDatabase checkDB = null;
105         String myPath = DB_PATH + DB_NAME;
106         try{            
107             checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
108         }catch(SQLiteException e){
109             //database does't exist yet.
110         }
111         if(checkDB != null){
112             checkDB.close();
113         }
114          return checkDB != null ? true : false;
115     }
116  
117     /**
118      * Copies your database from your local assets-folder to the just created empty database in the
119      * system folder, from where it can be accessed and handled.
120      * This is done by transfering bytestream.
121      * */
122     private void copyDataBase() throws IOException{
123         //Open your local db as the input stream
124         InputStream myInput = myContext.getAssets().open(ASSETS_NAME);
125         // Path to the just created empty db
126         String outFileName = DB_PATH + DB_NAME;
127         //Open the empty db as the output stream
128         OutputStream myOutput = new FileOutputStream(outFileName);
129         //transfer bytes from the inputfile to the outputfile
130         byte[] buffer = new byte[1024];
131         int length;
132         while ((length = myInput.read(buffer))>0){
133             myOutput.write(buffer, 0, length);
134         }
135         //Close the streams
136         myOutput.flush();
137         myOutput.close();
138         myInput.close();
139     }
140     
141     //复制assets下的大数据库文件时用这个
142     private void copyBigDataBase() throws IOException{
143         InputStream myInput;
144         String outFileName = DB_PATH + DB_NAME;
145         OutputStream myOutput = new FileOutputStream(outFileName);
146         for (int i = ASSETS_SUFFIX_BEGIN; i < ASSETS_SUFFIX_END+1; i++) {
147             myInput = myContext.getAssets().open(ASSETS_NAME + "." + i);
148             byte[] buffer = new byte[1024];
149             int length;
150             while ((length = myInput.read(buffer))>0){
151                 myOutput.write(buffer, 0, length);
152             }
153             myOutput.flush();
154             myInput.close();
155         }
156         myOutput.close();
157     }
158     
159     @Override
160     public synchronized void close() {
161         if(myDataBase != null){
162             myDataBase.close();
163         }
164         super.close();
165     }
166     
167     /**
168      * 该函数是在第一次创建的时候执行，
169      * 实际上是第一次得到SQLiteDatabase对象的时候才会调用这个方法
170      */
171     @Override
172     public void onCreate(SQLiteDatabase db) {
173     }
174     
175     /**
176      * 数据库表结构有变化时采用
177      */
178     @Override
179     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
180     }
181 
182 }
183