3.27

一、后端 REST API 设计（分页与同步）
为 Android 客户端提供增量数据同步接口，减少流量消耗：
java
// 数据同步控制器
@RestController
@RequestMapping("/api/sync")
public class SyncController {
@Autowired
private UserRepository userRepository;

// 获取增量数据（基于时间戳）
@GetMapping("/users")
public ResponseEntity<List<User>> getUpdatedUsers(
        @RequestParam("lastSyncTime") Long lastSyncTime) {
    LocalDateTime time = LocalDateTime.ofEpochSecond(lastSyncTime / 1000, 0, ZoneOffset.UTC);
    List<User> users = userRepository.findByUpdateTimeAfter(time);
    return ResponseEntity.ok(users);
}

// 批量更新数据
@PostMapping("/users")
public ResponseEntity<String> batchUpdateUsers(@RequestBody List<User> users) {
    userRepository.saveAll(users);
    return ResponseEntity.ok("更新成功，共" + users.size() + "条数据");
}

}
二、Android 端本地数据库设计（Room）
使用 Room 库实现本地数据存储与同步：
java
// 用户数据实体
@Entity(tableName = "users")
public class User {
@PrimaryKey
private Long id;
private String username;
private String email;
@ColumnInfo(name = "update_time")
private Long updateTime;
// getter和setter省略...
}

// 数据访问对象
@Dao
public interface UserDao {
@Query("SELECT * FROM users")
List getAll();

@Query("SELECT * FROM users WHERE id = :id")
User findById(Long id);

@Insert(onConflict = OnConflictStrategy.REPLACE)
long insert(User user);

@Insert(onConflict = OnConflictStrategy.REPLACE)
long[] insertAll(List<User> users);

@Query("DELETE FROM users")
void deleteAll();

}

// 数据库实例
@Database(entities = {User.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
private static final String DATABASE_NAME = "demo_database";
private static volatile AppDatabase instance;

public abstract UserDao userDao();

public static AppDatabase getInstance(Context context) {
    if (instance == null) {
        synchronized (AppDatabase.class) {
            if (instance == null) {
                instance = Room.databaseBuilder(
                        context.getApplicationContext(),
                        AppDatabase.class,
                        DATABASE_NAME)
                        .fallbackToDestructiveMigration()
                        .build();
            }
        }
    }
    return instance;
}

}
三、数据同步流程实现
同步工具类：
java
public class DataSyncManager {
private static final long MIN_SYNC_INTERVAL = 5 * 60 * 1000; // 5分钟
private Context context;
private ApiService apiService;
private AppDatabase database;
private long lastSyncTime;

public DataSyncManager(Context context) {
    this.context = context;
    this.apiService = RetrofitClient.getApiService();
    this.database = AppDatabase.getInstance(context);
    this.lastSyncTime = PreferenceManager.getDefaultSharedPreferences(context)
            .getLong("last_sync_time", 0);
}

public void syncData() {
    long currentTime = System.currentTimeMillis();
    if (currentTime - lastSyncTime < MIN_SYNC_INTERVAL) {
        return; // 未到最小同步间隔
    }
    
    // 1. 上传本地修改的数据
    uploadLocalChanges();
    
    // 2. 下载服务器更新的数据
    downloadServerUpdates();
    
    // 3. 保存同步时间
    PreferenceManager.getDefaultSharedPreferences(context)
            .edit()
            .putLong("last_sync_time", currentTime)
            .apply();
    lastSyncTime = currentTime;
}

private void uploadLocalChanges() {
    // 获取本地修改的数据
    List<User> localUsers = database.userDao().getAll();
    if (localUsers.isEmpty()) return;
    
    // 调用API上传
    apiService.batchUpdateUsers(localUsers).enqueue(new Callback<ApiResponse<Void>>() {
        @Override
        public void onResponse(Call<ApiResponse<Void>> call, Response<ApiResponse<Void>> response) {
            if (response.isSuccessful()) {
                Log.d("DataSync", "本地数据上传成功");
            } else {
                Log.e("DataSync", "本地数据上传失败");
            }
        }
        
        @Override
        public void onFailure(Call<ApiResponse<Void>> call, Throwable t) {
            Log.e("DataSync", "上传网络错误", t);
        }
    });
}

private void downloadServerUpdates() {
    apiService.getUpdatedUsers(lastSyncTime).enqueue(new Callback<ApiResponse<List<User>>>() {
        @Override
        public void onResponse(Call<ApiResponse<List<User>>> call, Response<ApiResponse<List<User>>> response) {
            if (response.isSuccessful() && response.body() != null && response.body().getData() != null) {
                List<User> serverUsers = response.body().getData();
                if (!serverUsers.isEmpty()) {
                    // 更新本地数据库
                    database.userDao().insertAll(serverUsers);
                    Log.d("DataSync", "下载" + serverUsers.size() + "条更新数据");
                }
            }
        }
        
        @Override
        public void onFailure(Call<ApiResponse<List<User>>> call, Throwable t) {
            Log.e("DataSync", "下载网络错误", t);
        }
    });
}

}
在应用中触发同步：
java
// 在Application或定时任务中调用
DataSyncManager syncManager = new DataSyncManager(this);
syncManager.syncData();