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/*
* Copyright 2013 Jesse Morgan
*/
package com.p4square.grow.backend.db;
import java.io.IOException;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;
import com.netflix.astyanax.model.Column;
import com.netflix.astyanax.model.ColumnList;
import com.p4square.grow.provider.CollectionProvider;
import com.p4square.grow.provider.JsonEncodedProvider;
/**
* CollectionProvider implementation backed by a Cassandra ColumnFamily.
*
* @author Jesse Morgan <jesse@jesterpm.net>
*/
public class CassandraCollectionProvider<V> implements CollectionProvider<String, String, V> {
private final CassandraDatabase mDb;
private final String mCF;
private final Class<V> mClazz;
public CassandraCollectionProvider(CassandraDatabase db, String columnFamily, Class<V> clazz) {
mDb = db;
mCF = columnFamily;
mClazz = clazz;
}
@Override
public V get(String collection, String key) throws IOException {
String blob = mDb.getKey(mCF, collection, key);
return decode(blob);
}
@Override
public Map<String, V> query(String collection) throws IOException {
return query(collection, -1);
}
@Override
public Map<String, V> query(String collection, int limit) throws IOException {
Map<String, V> result = new LinkedHashMap<>();
ColumnList<String> row = mDb.getRow(mCF, collection);
if (!row.isEmpty()) {
int count = 0;
for (Column<String> c : row) {
if (limit >= 0 && ++count > limit) {
break; // Limit reached.
}
String key = c.getName();
String blob = c.getStringValue();
V obj = decode(blob);
result.put(key, obj);
}
}
return Collections.unmodifiableMap(result);
}
@Override
public void put(String collection, String key, V obj) throws IOException {
String blob = encode(obj);
mDb.putKey(mCF, collection, key, blob);
}
/**
* Encode the object as JSON.
*
* @param obj The object to encode.
* @return The JSON encoding of obj.
* @throws IOException if the object cannot be encoded.
*/
protected String encode(V obj) throws IOException {
if (mClazz == String.class) {
return (String) obj;
} else {
return JsonEncodedProvider.MAPPER.writeValueAsString(obj);
}
}
/**
* Decode the JSON string as an object.
*
* @param blob The JSON data to decode.
* @return The decoded object or null if blob is null.
* @throws IOException If an object cannot be decoded.
*/
protected V decode(String blob) throws IOException {
if (blob == null) {
return null;
}
if (mClazz == String.class) {
return (V) blob;
}
V obj = JsonEncodedProvider.MAPPER.readValue(blob, mClazz);
return obj;
}
}
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