海灘美女.jpg
一. 背景
RxCache 是一個支持 Java 和 Android 的 Local Cache 襟铭。
之前的文章給 Java 和 Android 構(gòu)建一個簡單的響應(yīng)式Local Cache曾詳細(xì)介紹過它。
RxCache 包含了兩級緩存： Memory 和 Persistence 俊性。
下圖是 rxcache-core 模塊的 uml 類圖
rxcache_uml.png
二. 持久層
RxCache 的持久層包括 Disk搪桂、DB透敌，分別單獨抽象了 Disk、DB 接口并繼承 Persistence踢械。
DB 接口:
package com.safframework.rxcache.persistence.db;
import com.safframework.rxcache.persistence.Persistence;
/**
* Created by tony on 2018/10/14.
*/
public interface DB extends Persistence {
}
在 RxCache 的持久層酗电，嘗試集成 Android 常用的持久層框架。
2.1 集成 greenDAO
greenDAO 是一款開源的面向 Android 的輕便内列、快捷的 ORM 框架撵术，將 Java 對象映射到 SQLite 數(shù)據(jù)庫。
首先德绿，創(chuàng)建一個緩存實體 CacheEntity ，它包含 id、key累魔、data屎飘、timestamp、expireTime个粱。其中 data 是待緩存的對象并轉(zhuǎn)換成 json 字符串古毛。
@Entity
public class CacheEntity {
@Id(autoincrement = true)
private Long id;
public String key;
public String data;// 對象轉(zhuǎn)換的 json 字符串
public Long timestamp;
public Long expireTime;
...... // getter 、setter
}
創(chuàng)建一個單例的 DBService 都许，并提供返回 CacheEntityDao 的方法稻薇。其實，crud 的邏輯也可以放在此處胶征。
public class DBService {
private static final String DB_NAME = "cache.db";
private static volatile DBService defaultInstance;
private DaoSession daoSession;
private DBService(Context context) {
DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(context, DB_NAME);
DaoMaster daoMaster = new DaoMaster(helper.getWritableDatabase());
daoSession = daoMaster.newSession();
}
public static DBService getInstance(Context context) {
if (defaultInstance == null) {
synchronized (DBService.class) {
if (defaultInstance == null) {
defaultInstance = new DBService(context.getApplicationContext());
}
}
}
return defaultInstance;
}
public CacheEntityDao getCacheEntityDao(){
return daoSession.getCacheEntityDao();
}
}
創(chuàng)建 GreenDAOImpl 實現(xiàn) DB 接口塞椎，實現(xiàn)真正的緩存邏輯。
import com.safframework.rxcache.config.Constant;
import com.safframework.rxcache.domain.Record;
import com.safframework.rxcache.domain.Source;
import com.safframework.rxcache.persistence.converter.Converter;
import com.safframework.rxcache.persistence.converter.GsonConverter;
import com.safframework.rxcache.persistence.db.DB;
import com.safframework.tony.common.utils.Preconditions;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
/**
* @FileName: com.safframework.rxcache4a.persistence.db.greendao.GreenDAOImpl
* @author: Tony Shen
* @date: 2018-10-15 11:50
* @version: V1.0 <描述當(dāng)前版本功能>
*/
public class GreenDAOImpl implements DB {
private CacheEntityDao dao;
private Converter converter;
public GreenDAOImpl(CacheEntityDao dao) {
this(dao,new GsonConverter());
}
public GreenDAOImpl(CacheEntityDao dao, Converter converter) {
this.dao = dao;
this.converter = converter;
}
@Override
public <T> Record<T> retrieve(String key, Type type) {
CacheEntity entity = dao.queryBuilder().where(CacheEntityDao.Properties.Key.eq(key)).unique();
if (entity==null) return null;
long timestamp = entity.timestamp;
long expireTime = entity.expireTime;
T result = null;
if (expireTime<0) { // 緩存的數(shù)據(jù)從不過期
String json = entity.data;
result = converter.fromJson(json,type);
} else {
if (timestamp + expireTime > System.currentTimeMillis()) { // 緩存的數(shù)據(jù)還沒有過期
String json = entity.data;
result = converter.fromJson(json,type);
} else { // 緩存的數(shù)據(jù)已經(jīng)過期
evict(key);
}
}
return result != null ? new Record<>(Source.PERSISTENCE, key, result, timestamp, expireTime) : null;
}
@Override
public <T> void save(String key, T value) {
save(key,value, Constant.NEVER_EXPIRE);
}
@Override
public <T> void save(String key, T value, long expireTime) {
if (Preconditions.isNotBlanks(key,value)) {
CacheEntity entity = new CacheEntity();
entity.setKey(key);
entity.setTimestamp(System.currentTimeMillis());
entity.setExpireTime(expireTime);
entity.setData(converter.toJson(value));
dao.save(entity);
}
}
@Override
public List<String> allKeys() {
List<CacheEntity> list = dao.loadAll();
List<String> result = new ArrayList<>();
for (CacheEntity entity:list) {
result.add(entity.key);
}
return result;
}
@Override
public boolean containsKey(String key) {
List<String> keys = allKeys();
return Preconditions.isNotBlank(keys) ? keys.contains(key) : false;
}
@Override
public void evict(String key) {
CacheEntity entity = dao.queryBuilder().where(CacheEntityDao.Properties.Key.eq(key)).unique();
if (entity!=null) {
dao.delete(entity);
}
}
@Override
public void evictAll() {
dao.deleteAll();
}
}
2.2 集成 Room
Room 是 Google 開發(fā)的一個 SQLite 對象映射庫睛低。 使用它來避免樣板代碼并輕松地將 SQLite 數(shù)據(jù)轉(zhuǎn)換為 Java 對象案狠。 Room 提供 SQLite 語句的編譯時檢查，可以返回 RxJava 和 LiveData Observable钱雷。
同樣骂铁，需要先創(chuàng)建一個 CacheEntity，但是不能共用之前的 CacheEntity罩抗。因為 Room拉庵、greenDAO 使用的 @Entity不同。
@Entity
public class CacheEntity {
@PrimaryKey(autoGenerate = true)
private Long id;
public String key;
public String data;// 對象轉(zhuǎn)換的 json 字符串
public Long timestamp;
public Long expireTime;
...... // getter 套蒂、setter
}
創(chuàng)建一個 CacheEntityDao 用于 crud 的實現(xiàn)钞支。
import java.util.List;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import static androidx.room.OnConflictStrategy.IGNORE;
/**
* @FileName: com.safframework.rxcache4a.persistence.db.room.CacheEntityDao
* @author: Tony Shen
* @date: 2018-10-15 16:44
* @version: V1.0 <描述當(dāng)前版本功能>
*/
@Dao
public interface CacheEntityDao {
@Query("SELECT * FROM cacheentity")
List<CacheEntity> getAll();
@Query("SELECT * FROM cacheentity WHERE `key` = :key LIMIT 0,1")
CacheEntity findByKey(String key);
@Insert(onConflict = IGNORE)
void insert(CacheEntity entity);
@Delete
void delete(CacheEntity entity);
@Query("DELETE FROM cacheentity")
void deleteAll();
}
創(chuàng)建一個 AppDatabase 表示一個數(shù)據(jù)庫的持有者。
import androidx.room.Database;
import androidx.room.RoomDatabase;
/**
* @FileName: com.safframework.rxcache4a.persistence.db.room.AppDatabase
* @author: Tony Shen
* @date: 2018-10-15 16:40
* @version: V1.0 <描述當(dāng)前版本功能>
*/
@Database(entities = {CacheEntity.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
public abstract CacheEntityDao cacheEntityDao();
}
最后操刀，創(chuàng)建 RoomImpl 實現(xiàn) DB 接口伸辟，實現(xiàn)真正的緩存邏輯。
import android.content.Context;
import com.safframework.rxcache.config.Constant;
import com.safframework.rxcache.domain.Record;
import com.safframework.rxcache.domain.Source;
import com.safframework.rxcache.persistence.converter.Converter;
import com.safframework.rxcache.persistence.converter.GsonConverter;
import com.safframework.rxcache.persistence.db.DB;
import com.safframework.tony.common.utils.Preconditions;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import androidx.room.Room;
/**
* @FileName: com.safframework.rxcache4a.persistence.db.room.RoomImpl
* @author: Tony Shen
* @date: 2018-10-15 16:46
* @version: V1.0 <描述當(dāng)前版本功能>
*/
public class RoomImpl implements DB {
private AppDatabase db;
private Converter converter;
private static final String DB_NAME = "cache";
public RoomImpl(Context context) {
this(context,new GsonConverter());
}
public RoomImpl(Context context, Converter converter) {
this.db = Room.databaseBuilder(context, AppDatabase.class, DB_NAME).build();
this.converter = converter;
}
@Override
public <T> Record<T> retrieve(String key, Type type) {
CacheEntity entity = db.cacheEntityDao().findByKey(key);
if (entity==null) return null;
long timestamp = entity.timestamp;
long expireTime = entity.expireTime;
T result = null;
if (expireTime<0) { // 緩存的數(shù)據(jù)從不過期
String json = entity.data;
result = converter.fromJson(json,type);
} else {
if (timestamp + expireTime > System.currentTimeMillis()) { // 緩存的數(shù)據(jù)還沒有過期
String json = entity.data;
result = converter.fromJson(json,type);
} else { // 緩存的數(shù)據(jù)已經(jīng)過期
evict(key);
}
}
return result != null ? new Record<>(Source.PERSISTENCE, key, result, timestamp, expireTime) : null;
}
@Override
public <T> void save(String key, T value) {
save(key,value, Constant.NEVER_EXPIRE);
}
@Override
public <T> void save(String key, T value, long expireTime) {
if (Preconditions.isNotBlanks(key,value)) {
CacheEntity entity = new CacheEntity();
entity.setKey(key);
entity.setTimestamp(System.currentTimeMillis());
entity.setExpireTime(expireTime);
entity.setData(converter.toJson(value));
db.cacheEntityDao().insert(entity);
}
}
@Override
public List<String> allKeys() {
List<CacheEntity> list = db.cacheEntityDao().getAll();
List<String> result = new ArrayList<>();
for (CacheEntity entity:list) {
result.add(entity.key);
}
return result;
}
@Override
public boolean containsKey(String key) {
List<String> keys = allKeys();
return Preconditions.isNotBlank(keys) ? keys.contains(key) : false;
}
@Override
public void evict(String key) {
CacheEntity entity = db.cacheEntityDao().findByKey(key);
if (entity!=null) {
db.cacheEntityDao().delete(entity);
}
}
@Override
public void evictAll() {
db.cacheEntityDao().deleteAll();
}
}
這兩種集成方式馍刮，都使用 CacheEntity 的 data 來存儲對象轉(zhuǎn)換后的 json 字符串信夫。使用這種方式，可以替換成任何的持久層框架卡啰。使得 DB 也可以成為 RxCache 的其中一級緩存静稻。
三. 使用
編寫單元測試，看一下集成 greenDAO 的效果匈辱。
分別測試多種對象的存儲振湾、帶 ExpireTime 的存儲。
import android.content.Context;
import android.support.test.InstrumentationRegistry;
import android.support.test.runner.AndroidJUnit4;
import com.safframework.rxcache.RxCache;
import com.safframework.rxcache.domain.Record;
import com.safframework.rxcache4a.persistence.db.greendao.CacheEntityDao;
import com.safframework.rxcache4a.persistence.db.greendao.DBService;
import com.safframework.rxcache4a.persistence.db.greendao.GreenDAOImpl;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNull;
/**
* @FileName: com.safframework.rxcache4a.GreenDAOImplTest
* @author: Tony Shen
* @date: 2018-10-15 18:51
* @version: V1.0 <描述當(dāng)前版本功能>
*/
@RunWith(AndroidJUnit4.class)
public class GreenDAOImplTest {
Context appContext;
DBService dbService;
@Before
public void setUp() {
appContext = InstrumentationRegistry.getTargetContext();
dbService = DBService.getInstance(appContext);
}
@Test
public void testWithObject() {
CacheEntityDao dao = dbService.getCacheEntityDao();
GreenDAOImpl impl = new GreenDAOImpl(dao);
impl.evictAll();
RxCache.config(new RxCache.Builder().persistence(impl));
RxCache rxCache = RxCache.getRxCache();
Address address = new Address();
address.province = "Jiangsu";
address.city = "Suzhou";
address.area = "Gusu";
address.street = "ren ming road";
User u = new User();
u.name = "tony";
u.password = "123456";
u.address = address;
rxCache.save("user",u);
Record<User> record = rxCache.get("user", User.class);
assertEquals(u.name, record.getData().name);
assertEquals(u.password, record.getData().password);
assertEquals(address.city, record.getData().address.city);
rxCache.save("address",address);
Record<Address> record2 = rxCache.get("address", Address.class);
assertEquals(address.city, record2.getData().city);
}
@Test
public void testWithExpireTime() {
CacheEntityDao dao = dbService.getCacheEntityDao();
GreenDAOImpl impl = new GreenDAOImpl(dao);
impl.evictAll();
RxCache.config(new RxCache.Builder().persistence(impl));
RxCache rxCache = RxCache.getRxCache();
User u = new User();
u.name = "tony";
u.password = "123456";
rxCache.save("test",u,2000);
try {
Thread.sleep(2500);
} catch (InterruptedException e) {
e.printStackTrace();
}
Record<User> record = rxCache.get("test", User.class);
assertNull(record);
}
}
兩個 test case 都順利通過亡脸，表示集成 greenDAO 沒有問題押搪。當(dāng)然树酪，集成 Room 也是一樣。
四. 總結(jié)
我單獨創(chuàng)建了一個項目 RxCache4a 用于整合的 greenDAO大州、Room 等续语。
Github 地址: https://github.com/fengzhizi715/RxCache4a
未來，可能對框架增加一些 Annotation厦画，以及增加 Cache 清除的算法疮茄。
