面向对象式手写数据库架构

android中使用sqlite作为数据库存储数据，操作数据库最常见的是继承SqliteOpenHelper实现数据库表的操作，网上也有很多框架比如litepal，GreenDao等等。
现在我们自己实现类似的数据库框架

大致框架图

主要用到泛型、反射、注解。

编写注解DbTable,获取实体类名上的表名

package com.tony.dbdemo.db.annotion;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * Created by Tony on 2017/6/4. *///TYPE:用在类名上@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)public @interface DbTable {    String value();}

编写注解DbField,获取实体类字段上的表的列名

package com.tony.dbdemo.db.annotion;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/** * Created by Tony on 2017/6/4. */@Target(ElementType.FIELD)@Retention(RetentionPolicy.RUNTIME)public @interface DbField {    String value();}

编写实体类User
字段不能为private修饰，否则反射Class.getFields()拿不到字段

import com.tony.dbdemo.db.annotion.DbTable;/** * Created by Tony on 2017/6/4. */@DbTable("tb_user")public class User {    @DbField("name")    public String name;    @DbField("password")    public String password;    public User(String name,String password){        this.name = name;        this.password = password;    }    public User(){    }}

定义接口IBaseDao.java

package com.tony.dbdemo.db;import java.util.List;/** * Created by Tony on 2017/6/4. */public interface IBaseDao<T> {    /**     * 插入对象到数据库     * @param entity     * @return             */    Long insert(T entity);    /**     * 修改数据     * @param entity     * @param where     * @return     */    int update(T entity,T where);    /**     * 删除数据     * @param where     * @return     */    int delete(T where);    /**     * 查询数据     */    List<T> query(T where);    List<T> query(T where,String orderBy,Integer startIndex,Integer limit);}

定义实现IBaseDao的类BaseDao.java

package com.tony.dbdemo.db;import android.content.ContentValues;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.text.TextUtils;import com.tony.dbdemo.db.annotion.DbField;import com.tony.dbdemo.db.annotion.DbTable;import java.lang.reflect.Field;import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;/** * Created by Administrator on 2017/1/9 0009. */public abstract class BaseDao<T> implements  IBaseDao<T> {    /**]     * 持有数据库操作类的引用     */    private SQLiteDatabase database;    /**     * 保证实例化一次     */    private boolean isInit=false;    /**     * 持有操作数据库表所对应的java类型     * User     */    private Class<T> entityClass;    /**     * 维护这表名与成员变量名的映射关系     * key---》表名     * value --》Field     */    private HashMap<String,Field> cacheMap;    private String tableName;    /**     * @param entity     * @param sqLiteDatabase     * @return     * 实例化一次     */    protected synchronized boolean init(Class<T> entity, SQLiteDatabase sqLiteDatabase)    {        if(!isInit)        {            entityClass=entity;            database=sqLiteDatabase;            if (entity.getAnnotation(DbTable.class)==null)            {               tableName=entity.getClass().getSimpleName();            }else            {                tableName=entity.getAnnotation(DbTable.class).value();            }              if(!database.isOpen())              {                  return  false;              }                if(!TextUtils.isEmpty(createTable()))                {                    database.execSQL(createTable());                }              cacheMap=new HashMap<>();              initCacheMap();            isInit=true;        }        return  isInit;    }    /**     * 维护映射关系     */    private void initCacheMap() {        String sql="select * from "+this.tableName+" limit 1 , 0";        Cursor cursor=null;        try {            cursor=database.rawQuery(sql,null);            /**             * 表的列名数组             */            String[] columnNames=cursor.getColumnNames();            /**             * 拿到Filed数组             */            Field[] colmunFields=entityClass.getFields();            for(Field filed:colmunFields)            {                 filed.setAccessible(true);            }            /**             * 开始找对应关系             */            for(String colmunName:columnNames)            {                /**                 * 如果找到对应的Filed就赋值给他                 * User                 */                 Field colmunFiled=null;                for (Field field:colmunFields)                {                    String fieldName=null;                    if(field.getAnnotation(DbField.class)!=null)                    {                         fieldName=field.getAnnotation(DbField.class).value();                    }else                    {                        fieldName =field.getName();                    }                    /**                     * 如果表的列名 等于了  成员变量的注解名字                     */                    if(colmunName.equals(fieldName))                    {                        colmunFiled= field;                        break;                    }                }                //找到了对应关系                if(colmunFiled!=null)                {                    cacheMap.put(colmunName,colmunFiled);                }            }        }catch (Exception e)        {        }finally {            cursor.close();        }    }    @Override    public Long insert(T entity) {        Map<String,String> map=getValues(entity);        ContentValues values=getContentValues(map);        Long result =database.insert(tableName,null,values);        return result;    }    /**     * 讲map 转换成ContentValues     * @param map     * @return     */    private ContentValues getContentValues(Map<String, String> map) {        ContentValues contentValues=new ContentValues();        Set keys=map.keySet();        Iterator<String> iterator=keys.iterator();        while (iterator.hasNext())        {            String key=iterator.next();            String value=map.get(key);            if(value!=null)            {                contentValues.put(key,value);            }        }       return contentValues;    }    /**     * 创建表     * @return     */    protected  abstract  String createTable();    private Map<String, String> getValues(T entity) {        HashMap<String,String> result=new HashMap<>();        Iterator<Field> filedsIterator=cacheMap.values().iterator();        /**         * 循环遍历 映射map的  Filed         */        while (filedsIterator.hasNext())        {            /**             *             */            Field colmunToFiled=filedsIterator.next();            String cacheKey=null;            String cacheValue=null;            if(colmunToFiled.getAnnotation(DbField.class)!=null)            {                cacheKey=colmunToFiled.getAnnotation(DbField.class).value();            }else            {                cacheKey=colmunToFiled.getName();            }            try {                if(null==colmunToFiled.get(entity))                {                    continue;                }                cacheValue=colmunToFiled.get(entity).toString();            } catch (IllegalAccessException e) {                e.printStackTrace();            }            result.put(cacheKey,cacheValue);        }        return result;    }    @Override    public int update(T entity, T where) {        int result = -1;        Map values = getValues(entity);        /**         * 将条件对象 转换map         */        Map whereClause = getValues(where);        Condition condition = new Condition(whereClause);        ContentValues contentValues = getContentValues(values);        result = database.update(tableName,contentValues,condition.getWhereClause(),condition.getWhereArgs());        return result;    }    @Override    public int delete(T where) {        Map map = getValues(where);        Condition condition = new Condition(map);        int result = database.delete(tableName,condition.getWhereClause(),condition.getWhereArgs());        return result;    }    @Override    public List<T> query(T where) {        return query(where,null,null,null);    }    @Override    public List<T> query(T where, String orderBy, Integer startIndex, Integer limit) {       Map map = getValues(where);        String limitString = null;        if (startIndex != null && limit != null){            limitString = startIndex+" , "+limit;        }        Condition condition = new Condition(map);        Cursor cursor = database.query(tableName,null,condition.getWhereClause(),condition.getWhereArgs(),null,null,orderBy,limitString);        List<T> result = getResult(cursor,where);        cursor.close();        return result;    }    private List<T> getResult(Cursor cursor, T where) {        ArrayList list = new ArrayList();        Object item;        while (cursor.moveToNext())        {            try {                item = where.getClass().newInstance();                /**                 * 列名 name                 * 成员变量 Field                 */                Iterator iterator = cacheMap.entrySet().iterator();                while (iterator.hasNext())                {                    Map.Entry entry = (Map.Entry) iterator.next();                    /**                     * 得到列名                     */                    String columnName = (String) entry.getKey();                    /**                     * 然后以列名拿到 列名在游标的位置                     */                    Integer columnIndex = cursor.getColumnIndex(columnName);                    Field field = (Field) entry.getValue();                    Class type = field.getType();                    if (columnIndex!=-1){                        if (type == String.class)                        {                            //反射方式赋值                            field.set(item,cursor.getString(columnIndex));                        }else if (type == Double.class){                            field.set(item,cursor.getDouble(columnIndex));                        }else if (type == Integer.class){                            field.set(item,cursor.getInt(columnIndex));                        }else if (type == Long.class){                            field.set(item,cursor.getLong(columnIndex));                        }else if (type == byte[].class){                            field.set(item,cursor.getBlob(columnIndex));                        }else {                            /**                             * 不支持的类型                             */                            continue;                        }                    }                }                list.add(item);            } catch (InstantiationException e) {                e.printStackTrace();            } catch (IllegalAccessException e) {                e.printStackTrace();            }        }        return list;    }    /**     * 封装修改语句     */    class Condition    {        /**         * 查询条件         * name=？&&password=？         */        private String whereClause;        /**         * 参数         */        private String[] whereArgs;        public Condition(Map<String,String> whereClause) {            ArrayList list = new ArrayList();            StringBuilder stringBuilder = new StringBuilder();            stringBuilder.append(" 1=1 ");            Set keys = whereClause.keySet();            Iterator iterator = keys.iterator();            while (iterator.hasNext()){               String key = (String) iterator.next();                String value = whereClause.get(key);                if (value!=null){                    /**                     * 拼接条件查询语句                     */                    stringBuilder.append(" and "+key+" =?");                    list.add(value);                }            }            this.whereClause = stringBuilder.toString();            //list转化为你所需要类型的数组            this.whereArgs = (String[]) list.toArray(new String[list.size()]);        }        public String getWhereClause() {            return whereClause;        public void setWhereClause(String whereClause) {            this.whereClause = whereClause;        }        public String[] getWhereArgs() {            return whereArgs;        }        public void setWhereArgs(String[] whereArgs) {            this.whereArgs = whereArgs;        }    }}

定义BaseDaoFactory初始化BaseDao

package com.tony.dbdemo.db;import android.database.sqlite.SQLiteDatabase;import android.os.Environment;/** * Created by Tony on 2017/6/4. */public class BaseDaoFactory {    private String sqliteDatabasePath;    private SQLiteDatabase sqLiteDatabase;    private static BaseDaoFactory Instence = new BaseDaoFactory();    public static BaseDaoFactory getInstence(){        return Instence;    }    public BaseDaoFactory(){        sqliteDatabasePath = Environment.getExternalStorageDirectory().getAbsolutePath()+"/teacher.db";        openDatabase();    }    private void openDatabase() {        this.sqLiteDatabase = SQLiteDatabase.openOrCreateDatabase(sqliteDatabasePath,null);    }    public synchronized <T extends BaseDao<M>,M> T getDataHelper(Class<T> clazz, Cass<M> entityClass){        BaseDao baseDao = null;        try {            baseDao = clazz.newInstance();            baseDao.init(entityClass,sqLiteDatabase);        } catch (InstantiationException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }        return (T) baseDao;    }}

MainActivity测试

package com.tony.dbdemo;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import android.view.View;import com.tony.dbdemo.Bean.File;import com.tony.dbdemo.Bean.User;import com.tony.dbdemo.Dao.FileDao;import com.tony.dbdemo.Dao.UserDao;import com.tony.dbdemo.db.BaseDaoFactory;import com.tony.dbdemo.db.IBaseDao;import java.util.List;public class MainActivity extends AppCompatActivity {    IBaseDao<User> baseDao;    IBaseDao<File> fileDao;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        baseDao = BaseDaoFactory.getInstence().getDataHelper(UserDao.class,User.class);        //fileDao = BaseDaoFactory.getInstence().getDataHelper(FileDao.class,File.class);    }    public void save(View v){        for (int i = 0; i < 10; i++) {            User user = new User(i+1,"Tony"+i,"123456");            baseDao.insert(user);        }        /*File file = new File("2017-6-5","data/data/path","插入文件操作记录");        fileDao.insert(file);*/    }    public void update(View v){        User where = new User();        where.userId=1;        User user = new User(2,"David","123456789");        baseDao.update(user,where);    }    public void delete(View v){     User user = new User();        user.name="David";        baseDao.delete(user);    }    public void query(View v){        User where = new User();        where.name="David";        where.userId=1;        List<User> list = baseDao.query(where);        Log.i(MainActivity.class.getName(),"查询到 "+list.size()+" 条数据");        for (User user : list){            Log.i(MainActivity.class.getName(),user.toString());        }    }}

布局文件

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical"    tools:context="com.tony.dbdemo.MainActivity">    <Button        android:layout_width="246dp"        android:layout_height="45dp"        android:text="save"        android:onClick="save"        android:layout_gravity="center"       />    <Button        android:layout_width="246dp"        android:layout_height="43dp"        android:text="update"        android:onClick="update"        android:layout_gravity="center"        />    <Button        android:layout_width="246dp"        android:layout_height="43dp"        android:text="delete"        android:onClick="delete"        android:layout_gravity="center"        />    <Button        android:layout_width="246dp"        android:layout_height="43dp"        android:text="query"        android:onClick="query"        android:layout_gravity="center"        /></LinearLayout>

源码地址：https://github.com/fsdsds/DBDemo