Đầu tiên kiểm tra các thiết bị được kết nối từ internet hay không.
public class Reachability {
private final ConnectivityManager mConnectivityManager;
public Reachability(Context context) {
mConnectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
}
public boolean isConnected() {
NetworkInfo networkInfo = mConnectivityManager.getActiveNetworkInfo();
return networkInfo != null && networkInfo.isConnectedOrConnecting();
}}
Nếu thiết bị được kết nối từ internet thì lấy dữ liệu từ API và lưu vào bộ nhớ cache để lấy dữ liệu từ bộ nhớ cache.
public class CacheManager {
Cache<String, String> mCache;
private DiskLruCache mDiskLruCache;
private final Context mContext;
public CacheManager(Context context) throws IOException {
mContext = context;
setUp();
mCache = DiskCache.getInstanceUsingDoubleLocking(mDiskLruCache);
}
public void setUp() throws IOException {
File cacheInFiles = mContext.getFilesDir();
int version = BuildConfig.VERSION_CODE;
int KB = 1024;
int MB = 1024 * KB;
int cacheSize = 400 * MB;
mDiskLruCache = DiskLruCache.open(cacheInFiles, version, 1, cacheSize);
}
public Cache<String, String> getCache() {
return mCache;
}
public static class DiskCache implements Cache<String, String> {
private static DiskLruCache mDiskLruCache;
private static DiskCache instance = null;
public static DiskCache getInstanceUsingDoubleLocking(DiskLruCache diskLruCache){
mDiskLruCache = diskLruCache;
if(instance == null){
synchronized (DiskCache.class) {
if(instance == null){
instance = new DiskCache();
}
}
}
return instance;
}
@Override
public synchronized void put(String key, String value) {
try {
if (mDiskLruCache != null) {
DiskLruCache.Editor edit = mDiskLruCache.edit(getMd5Hash(key));
if (edit != null) {
edit.set(0, value);
edit.commit();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public synchronized String get(String key) {
try {
if (mDiskLruCache != null) {
DiskLruCache.Snapshot snapshot = mDiskLruCache.get(getMd5Hash(key));
if (snapshot == null) {
// if there is a cache miss simply return null;
return null;
}
return snapshot.getString(0);
}
} catch (IOException e) {
e.printStackTrace();
}
// in case of error in reading return null;
return null;
}
@Override
public String remove(String key) {
// TODO: implement
return null;
}
@Override
public void clear() {
// TODO: implement
}
}
public static String getMd5Hash(String input) {
try {
MessageDigest md = MessageDigest.getInstance("MD5");
byte[] messageDigest = md.digest(input.getBytes());
BigInteger number = new BigInteger(1, messageDigest);
String md5 = number.toString(16);
while (md5.length() < 32)
md5 = "0" + md5;
return md5;
} catch (NoSuchAlgorithmException e) {
Log.e("MD5", e.getLocalizedMessage());
return null;
}
}}
Tạo lớp CacheInterceptor để cache phản hồi mạng và xử lý các lỗi
public class CacheInterceptor implements Interceptor{
private final CacheManager mCacheManager;
private final Reachability mReachability;
public CacheInterceptor(CacheManager cacheManager, Reachability reachability) {
mCacheManager = cacheManager;
mReachability = reachability;
}
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
String key = request.url().toString();
Response response;
if (mReachability.isConnected()) {
try {
response = chain.proceed(request);
Response newResponse = response.newBuilder().build();
if (response.isSuccessful()) {
if (response.code() == 204) {
return response;
}
// save to cache this success model.
mCacheManager.getCache().put(key, newResponse.body().string());
// now we know that we definitely have a cache hit.
return getCachedResponse(key, request);
}else if (response.code() >= 500) { // accommodate all server errors
// check if there is a cache hit or miss.
if (isCacheHit(key)) {
// if data is in cache, the return the data from cache.
return getCachedResponse(key, request);
}else {
// if it's a miss, we can't do much but return the server state.
return response;
}
}else { // if there is any client side error
// forward the response as it is to the business layers to handle.
return response;
}
} catch (ConnectException | UnknownHostException e) {
// Internet connection exception.
e.printStackTrace();
}
}
// if somehow there is an internet connection error
// check if the data is already cached.
if (isCacheHit(key)) {
return getCachedResponse(key, request);
}else {
// if the data is not in the cache we'll throw an internet connection error.
throw new UnknownHostException();
}
}
private Response getCachedResponse(String url, Request request) {
String cachedData = mCacheManager.getCache().get(url);
return new Response.Builder().code(200)
.body(ResponseBody.create(MediaType.parse("application/json"), cachedData))
.request(request)
.protocol(Protocol.HTTP_1_1)
.build();
}
public boolean isCacheHit(String key) {
return mCacheManager.getCache().get(key) != null;
}}
Bây giờ thêm đánh chặn này trong OkHttpClient trong khi tạo ra các dịch vụ sử dụng Retrofit.
public final class ServiceManager {
private static ServiceManager mServiceManager;
public static ServiceManager get() {
if (mServiceManager == null) {
mServiceManager = new ServiceManager();
}
return mServiceManager;
}
public <T> T createService(Class<T> clazz, CacheManager cacheManager, Reachability reachability) {
return createService(clazz, HttpUrl.parse(ServiceApiEndpoint.SERVICE_ENDPOINT), cacheManager, reachability);
}
private <T> T createService(Class<T> clazz, HttpUrl parse, CacheManager cacheManager, Reachability reachability) {
Retrofit retrofit = getRetrofit(parse, cacheManager, reachability);
return retrofit.create(clazz);
}
public <T> T createService(Class<T> clazz) {
return createService(clazz, HttpUrl.parse(ServiceApiEndpoint.SERVICE_ENDPOINT));
}
private <T> T createService(Class<T> clazz, HttpUrl parse) {
Retrofit retrofit = getRetrofit(parse);
return retrofit.create(clazz);
}
private <T> T createService(Class<T> clazz, Retrofit retrofit) {
return retrofit.create(clazz);
}
private Retrofit getRetrofit(HttpUrl httpUrl, CacheManager cacheManager, Reachability reachability) {
return new Retrofit.Builder()
.baseUrl(httpUrl)
.client(createClient(cacheManager, reachability))
.addConverterFactory(getConverterFactory())
.build();
}
private OkHttpClient createClient(CacheManager cacheManager, Reachability reachability) {
return new OkHttpClient.Builder().addInterceptor(new CacheInterceptor(cacheManager, reachability)).build();
}
private Retrofit getRetrofit(HttpUrl parse) {
return new Retrofit.Builder()
.baseUrl(parse)
.client(createClient())
.addConverterFactory(getConverterFactory()).build();
}
private Retrofit getPlainRetrofit(HttpUrl httpUrl) {
return new Retrofit.Builder()
.baseUrl(httpUrl)
.client(new OkHttpClient.Builder().build())
.addConverterFactory(getConverterFactory())
.build();
}
private Converter.Factory getConverterFactory() {
return GsonConverterFactory.create();
}
private OkHttpClient createClient() {
return new OkHttpClient.Builder().build();
}}
giao diện bộ nhớ cache
public interface Cache<K, V> {
void put(K key, V value);
V get(K key);
V remove(K key);
void clear();}
Tuyệt vời! Bạn cũng có thể tìm thấy một số mẫu tốt của việc sử dụng Volley ở đây: https://github.com/stormzhang/AndroidVolley – Sam003