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* Extend from this class.
*
* public class ConnectionStore extends AbstractStore {
* ....
* }
*
* {code}
*
*
* Implement a few abstract methods relevant to the data being stored.
*
* @Override protected String getKeySpace() { ... }
* @Override protected String getDelimiter() { ... }
* @Override public String create(Connection connection) { ... }
* @Override public void update(String id, Connection connection) { ... }
* @Override public Connection clone(String id) { ... }
*
*
*
*/
public abstract class AbstractTableStore {
// Table in which all the object data is store.
private final Table table;
// Gson handler for converting object into JSON.
private final Gson gson;
// Column to which the data should be written.
private final byte[] column;
// Avoiding type erasure.
private final Class classz;
protected AbstractTableStore(Table table, byte[] column, Class classz) {
this.table = table;
this.column = column;
this.classz = classz;
gson = new GsonBuilder().registerTypeAdapter(Schema.class, new SchemaTypeAdapter()).create();
}
/**
* Converts object of type T to JSON string.
*
* @param object to be converted
* @return string representation of object.
*/
protected String toJson(T object) {
String json = gson.toJson(object);
return json;
}
/**
* Converts object of type T to byte array.
*
* @param object to be converted
* @return byte array representing JSON.
*/
protected byte[] toJsonBytes(T object) {
return Bytes.toBytes(toJson(object));
}
/**
* Converts from JSON string to object of type T.
*
* @param json string to be converted to object.
* @return instance of type T object.
*/
protected T fromJson(String json) {
return gson.fromJson(json, classz);
}
/**
* Converts from JSON byte array to object of type T.
*
* @param json byte array to be converted to object.
* @return instance of type T object.
*/
protected T fromJson(byte[] json) {
return fromJson(Bytes.toString(json));
}
/**
* Given a key, returns the object of type T from the table.
*
* @param key to be used to retrieve the object.
* @return instance of type T object if found, else returns null.
*/
protected T getObject(byte[] key) {
byte[] bytes = table.get(key, column);
if (bytes != null) {
return fromJson(bytes);
}
return null;
}
/**
* Given a key of type string, returns the object of type T from the table.
*
* @param key to be used to retrieve the object.
* @return instance of type T object if found, else returns null.
*/
protected T getObject(String key) {
return getObject(Bytes.toBytes(key));
}
/**
* Adds the object of type T to the table using the key represented as byte array.
*
* @param key to be used to store the object.
* @param object instance of the object to be stored.
*/
protected void putObject(byte[] key, T object) {
byte[] bytes = toJsonBytes(object);
table.put(generateKey(Bytes.toString(key)), column, bytes);
}
/**
* Generates a composite key that is a combination of namespace and object key.
*
* @param key specifies the key to be used to generate the composite key.
* @return composite key.
*/
protected byte[] generateKey(String key) {
String compositeKey = String.format("%s%s", getKeySpace(), key);
return Bytes.toBytes(compositeKey);
}
/**
* Mangles the name.
*
* @param name to be mangled.
* @return mangled name.
*/
protected String mangle(String name) {
name = name.trim();
// Lower case columns
name = name.toLowerCase();
// Filtering unwanted characters
name = name.replaceAll("[^a-zA-Z0-9_]", "_");
return name;
}
/**
* @return current time in seconds.
*/
protected long now() {
return System.currentTimeMillis() / 1000;
}
/**
* Updates the table given an id and connection instance.
*
* @param id of the key.
* @param object object to be stored.
*/
protected void updateTable(String id, T object) {
byte[] bytes = toJsonBytes(object);
table.put(generateKey(id), column, bytes);
}
/**
* @return Abstract method implemented by the extending class to provide the key namespace.
*/
protected abstract String getKeySpace();
/**
* Scans the namespace to list all the keys applying the filter.
*
* @param filter to be applied on the data being returned.
* @return List of objects of type T.
*/
public List scan(Predicate filter) {
List result = new ArrayList<>();
byte[] startKey = Bytes.toBytes(getKeySpace());
byte[] stopKey = Bytes.stopKeyForPrefix(startKey);
try (Scanner scan = table.scan(startKey, stopKey)) {
Row next;
while ((next = scan.next()) != null) {
byte[] bytes = next.get(column);
T object = fromJson(bytes);
if (filter != null) {
if(filter.apply(object)) {
result.add(object);
}
} else {
result.add(object);
}
}
}
return result;
}
/**
* Checks if the key is present in the store.
*
* @param id of the key to be checked.
* @return true if present, false otherwise.
*/
public boolean hasKey(String id) {
byte[] bytes = generateKey(id);
Row row = table.get(bytes);
if(row.isEmpty()) {
return false;
}
return true;
}
/**
* Deletes the object with key id from the table in the namespace.
*
* @param id of the object to be deleted.
*/
public void delete(String id) {
table.delete(generateKey(id));
}
/**
* Returns the instance of stored object of type T from the store.
*
* @param id of the object to be retrieved.
* @return instance of object of type T if present, else false.
*/
public T get(String id) {
return getObject(generateKey(id));
}
/**
* Creates an instance of the object of type T in the store.
* If the object already exits in the store, which is determined by looking at the key,
* then an exception is thrown.
*
* @param object to be created in the store.
* @return Id of the object that was created.
*/
public abstract String create(T object);
/**
* Updates the already existing object in the object store.
*
* @param id of the object to be updated.
* @param object itself to be updated.
*/
public abstract void update(String id, T object);
/**
* Clones the object with the id specified.
* NOTE: The object is not updated in the object store.
*
* @param id of the object to be cloned.
* @return instance of the newly created object.
*/
public abstract T clone(String id);
}
