SQLite数据库创建时自定义路径

前言

在新建数据库sqlite的时候,我们已经知道了数据库默认路径为

/data/data/com.example.pei.textdemo/databases/test_demo.db

那么,如果我们想在创建数据库时,自定义一个自己的路径该如何处理呢,需要涉及到三步

  • 自定义Context,重写sqlite存储路径
  • 修改继承于SQLiteOpenHelper的DBOpenHelper类
  • 数据库的调用
    下面就来讲讲具体操作。
一.自定义Context,重写sqlite存储路径

我们在创建数据库的时候,会涉及到一个类SQLiteOpenHelper,一般建数据库的时候,都要继承SQLiteOpenHelper实现一个自己的helper类,这里,我写一个自己的helper来继承SQLiteOpenHelper,部分代码如下:

public class DBOpenHelper extends SQLiteOpenHelper{
......
}

然后在DBOpenHelper这个类中,我们会有两个构造方法

   public DBOpenHelper(Context context) {
        this(context, DB_NAME, null, 1);
        this.mContext= context;
    }

    public DBOpenHelper(Context context, String dbName, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, dbName, factory, version);
    }

其中 mContext为Context,Context类会涉及到sqlite的储存路径,为了自定义数据库路径,我们需要实现一个自己的context,来自定义数据库路径,然而Context有一个子类ContextWrapper,可以方便用户对Context进行自定义,看源码中ContextWrapper继承关系如下:


/**
 * Proxying implementation of Context that simply delegates all of its calls to
 * another Context.  Can be subclassed to modify behavior without changing
 * the original Context.
 */
public class ContextWrapper extends Context {
    Context mBase;

    public ContextWrapper(Context base) {
        mBase = base;
    }

那么,我们就写一个类ContextWrapper来继承ContextWrapper实现自己的context,代码如下:

package com.example.pei.textdemo.sqlite;

import android.content.Context;
import android.content.ContextWrapper;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;

import com.example.pei.textdemo.util.SDCardUtil;

import java.io.File;

/**
 * Title:
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/20
 */
public class DataBaseContext extends ContextWrapper {

    private Context mContext;

    public DataBaseContext(Context context){
        super(context);
        this.mContext=context;
    }

    /**重写数据库路径方法**/
    @Override
    public File getDatabasePath(String name) {
//        String path1= SDCardUtil.getDiskFilePath(name);
//        String dirPath=path1.replace(name,"");

        String dirPath=SDCardUtil.getInnerSDCardPath();

        String path=null;
        File parentFile=new File(dirPath);
        if(!parentFile.exists()){
            parentFile.mkdirs();
        }
        String parentPath=parentFile.getAbsolutePath();
        if(parentPath.lastIndexOf("\\/")!=-1){
            path=dirPath + File.separator + name;
        }else{
            path=dirPath+name;
        }
        File file = new File(path);

        return file;
    }

    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
        return SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), factory);
    }

    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory, DatabaseErrorHandler errorHandler) {
        return SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name).getAbsolutePath(),factory,errorHandler);
    }

}

其中我们需要重写getDatabasePath(String name)方法来自定义自己的数据库存储路径,然后重写ContextWrapper 的两个openOrCreateDatabase方法,代码中SDCardUtil.getInnerSDCardPath()方法代码如下

  /**获取内置sdcard路径(数据会保存,应用删除的时候,数据不会被清理掉)**/
    public static String getInnerSDCardPath(){
        if(isSdcardExist()){
            //------/storage/emulated/0/
            return Environment.getExternalStorageDirectory() + File.separator;
        }
        return null;
    }
二.编写继承于SQLiteOpenHelper的DBOpenHelper类

我们需要用自己定义的DataBaseContext 来代替之前的 Context,代码如下:

package com.example.pei.textdemo.sqlite;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * Title:创建数据库
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/16
 */
public class DBOpenHelper extends SQLiteOpenHelper{

    private static final String DB_NAME = "tf_demo.db";//数据库文件名
    private static SQLiteDatabase INSTANCE;
    private DataBaseContext mContext;

    public SQLiteDatabase getInstance(){
        if (INSTANCE == null) {
            INSTANCE = new DBOpenHelper(mContext).getWritableDatabase();
        }
        return INSTANCE;
    }

    public DBOpenHelper(Context context) {
        this(context, DB_NAME, null, 1);
        this.mContext= (DataBaseContext) context;
    }

    public DBOpenHelper(Context context, String dbName, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, dbName, factory, version);
    }


    /**获取数据库路径**/
    public String getDBPath(){
        return mContext.getDatabasePath(DB_NAME).getAbsolutePath();
    }

    //首次创建数据库时调用,一般进行建库建表操作
    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE IF NOT EXISTS user(_id integer NOT NULL PRIMARY KEY AUTOINCREMENT,\n" +
                "                                name text,\n" +
                "                                sex text,\n" +
                "                                age integer);";
        //创建表
        db.execSQL(createTable);
    }

    //当数据库的版本发生变化的时候会自动执行,禁止人为调用
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

}

三.在DBHelper中调整DBOpenHelper的调用

代码如下:

package com.example.pei.textdemo.sqlite;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.example.pei.textdemo.app.AppContext;

import java.util.List;

/**
 * Title:数据库增删改查帮助类
 * Description:
 * <p>
 * Created by pei
 * Date: 2017/11/16
 */
public abstract class DBHelper {

    protected DBOpenHelper mDBOpenHelper;

    private DBOpenHelper getDBOpenHelper(){
        if(mDBOpenHelper==null){
//            mDBOpenHelper=new DBOpenHelper(AppContext.getInstance());
            mDBOpenHelper=new DBOpenHelper(new DataBaseContext(AppContext.getInstance()));
        }
        return mDBOpenHelper;
    }


    /**获取数据库对象**/
    protected SQLiteDatabase getDateBase(){
        return getDBOpenHelper().getInstance();
    }

    /**关闭数据库**/
    protected void closeDB(){
        SQLiteDatabase db = getDateBase();
        if(db!=null){
            db.close();
        }
    }

    /**
     * 判断表是否存在
     * @param tableName:表名
     * @return
     */
    protected boolean isTableExist(String tableName){
        Cursor cursor = getDateBase().rawQuery("select name from sqlite_master where type='table';", null);
        while(cursor.moveToNext()){
            //遍历出表名
            String name = cursor.getString(0);
            if(name.equals(tableName)){
                return true;
            }
        }
        return false;
    }

    /**查询**/
    protected abstract List<?> checkAll();
    /**添加**/
    protected abstract void insert(Object obj);
    /**删除**/
    protected abstract void delete(Object obj);
    /**更新**/
    protected abstract void update(Object obj);
}

然后,写一个自己的UserDBHelper类去继承DBHelper,来实现具体的增删改查,就可以愉快的调用了,以下是我写的一个UserDBHelper范例:

public class UserDBHelper extends DBHelper{

    private UserDBHelper() {
    }

    private static class Holder {
        private static UserDBHelper instance = new UserDBHelper();
    }

    public static UserDBHelper getInstance() {
        return Holder.instance;
    }

    @Override
    protected List<Person> checkAll() {
            List<Person> list = new ArrayList<>();
            //COLLATE NOCASE 忽略大小写查询
//            Cursor cursor = getDateBase().rawQuery("select * from T_cpz where isqy='True' COLLATE NOCASE;", null);
            Cursor cursor = getDateBase().rawQuery("select * from user", null);
            while (cursor.moveToNext()) {
                String name = cursor.getString(cursor.getColumnIndex("name"));
                String sex = cursor.getString(cursor.getColumnIndex("sex"));
                int age=cursor.getInt(cursor.getColumnIndex("age"));

                Person person=new Person();
                person.setName(name);
                person.setSex(sex);
                person.setAge(age);
                list.add(person);
            }
            cursor.close();
        return list;
    }

    @Override
    protected void insert(Object obj){
        Person person= (Person) obj;
        String sql="INSERT INTO user(name,sex,age) VALUES('"+ person.getName()+"','"+ person.getSex()+"','"+ person.getAge()+"');";
        getDateBase().execSQL(sql);
    }

    @Override
    protected void delete(Object obj) {
        Person person = (Person) obj;
        String sql = "DELETE FROM user WHERE name='" + person.getName() + "';";
        getDateBase().execSQL(sql);
    }

    @Override
    protected void update(Object obj) {
        Person person = (Person) obj;
        String sql="UPDATE user SET age="+person.getAge()+" WHERE name='"+person.getName()+"';";
        getDateBase().execSQL(sql);
    }

}

然后在activity中,你可以这样获取数据库存储路径

  String dbPath=UserDBHelper.getInstance().getDataBasePath();
  LogUtil.e("=====dbPath===000=="+dbPath);

当然,由于你自定义路径会涉及到存储的读写问题,所以要在mainfast总增加相应权限:

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

还要在代码中添加Android7.0以上权限,关于代码授权,这里就不做介绍了。

ok,关于sqlite自定义数据库路径,今天就讲到这里了,谢谢!

    原文作者:奔跑的佩恩
    原文地址: https://www.jianshu.com/p/602e2ed91f94
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。
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