/*
* Copyright (C) 2012-2015 DataStax Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.datastax.driver.examples.json;
import com.datastax.driver.core.*;
import com.datastax.driver.extras.codecs.json.JacksonJsonCodec;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.fasterxml.jackson.databind.node.ObjectNode;
import static com.datastax.driver.core.querybuilder.QueryBuilder.*;
/**
* Illustrates how to map a single table column of an arbitrary type
* to a Java object using
* the <a href="http://wiki.fasterxml.com/JacksonHome">Jackson</a> library,
* and leveraging the {@code toJson()} and {@code fromJson()} functions
* introduced in Cassandra 2.2.
* <p/>
* This example makes usage of a custom {@link TypeCodec codec},
* {@link JacksonJsonCodec}, which is declared in the driver-extras module.
* If you plan to follow this example, make sure to include the following
* Maven dependencies in your project:
* <pre>{@code
* <dependency>
* <groupId>com.datastax.cassandra</groupId>
* <artifactId>cassandra-driver-extras</artifactId>
* <version>${driver.version}</version>
* </dependency>
*
* <dependency>
* <groupId>com.fasterxml.jackson.core</groupId>
* <artifactId>jackson-databind</artifactId>
* <version>${jackson.version}</version>
* </dependency>
* }</pre>
* This example also uses the {@link com.datastax.driver.core.querybuilder.QueryBuilder QueryBuilder};
* for examples using the "core" API, see {@link PlainTextJson} (they are easily translatable to the
* queries in this class).
* <p/>
* Preconditions:
* - a Cassandra cluster is running and accessible through the contacts points identified by CONTACT_POINTS and PORT;
* <p/>
* Side effects:
* - creates a new keyspace "examples" in the cluster. If a keyspace with this name already exists, it will be reused;
* - creates a user-defined type (UDT) "examples.json_jackson_function_user". If it already exists, it will be reused;
* - creates a table "examples.json_jackson_function". If it already exists, it will be reused;
* - inserts data in the table.
*
* @see <a href="http://www.datastax.com/dev/blog/whats-new-in-cassandra-2-2-json-support">What’s New in Cassandra 2.2: JSON Support</a>
*/
public class JacksonJsonFunction {
static String[] CONTACT_POINTS = {"127.0.0.1"};
static int PORT = 9042;
public static void main(String[] args) {
Cluster cluster = null;
try {
// A codec to convert JSON payloads into User instances;
// this codec is declared in the driver-extras module
TypeCodec<User> userCodec = new JacksonJsonCodec<User>(User.class);
// A codec to convert generic JSON payloads into JsonNode instances
TypeCodec<JsonNode> jsonNodeCodec = new JacksonJsonCodec<JsonNode>(JsonNode.class);
cluster = Cluster.builder()
.addContactPoints(CONTACT_POINTS).withPort(PORT)
.withCodecRegistry(new CodecRegistry()
.register(userCodec)
.register(jsonNodeCodec))
.build();
Session session = cluster.connect();
createSchema(session);
insertFromJson(session);
selectToJson(session);
} finally {
if (cluster != null) cluster.close();
}
}
private static void createSchema(Session session) {
session.execute("CREATE KEYSPACE IF NOT EXISTS examples " +
"WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 1}");
session.execute("CREATE TYPE IF NOT EXISTS examples.json_jackson_function_user(" +
"name text, age int)");
session.execute("CREATE TABLE IF NOT EXISTS examples.json_jackson_function(" +
"id int PRIMARY KEY, user frozen<json_jackson_function_user>, scores map<varchar,float>)");
}
// Mapping JSON payloads to table columns of arbitrary types,
// using fromJson() function
private static void insertFromJson(Session session) {
User alice = new User("alice", 30);
User bob = new User("bob", 35);
ObjectNode aliceScores = JsonNodeFactory.instance.objectNode()
.put("call_of_duty", 4.8)
.put("pokemon_go", 9.7);
ObjectNode bobScores = JsonNodeFactory.instance.objectNode()
.put("zelda", 8.3)
.put("pokemon_go", 12.4);
// Build and execute a simple statement
Statement stmt = insertInto("examples", "json_jackson_function")
.value("id", 1)
// client-side, the User object will be converted into a JSON String;
// then, server-side, the fromJson() function will convert that JSON string
// into an instance of the json_jackson_function_user user-defined type (UDT),
// which will be persisted into the column "user"
.value("user", fromJson(alice))
// same thing, but this time converting from
// a generic JsonNode to a JSON string, then from this string to a map<varchar,float>
.value("scores", fromJson(aliceScores));
session.execute(stmt);
// The JSON object can be a bound value if the statement is prepared
// (we use a local variable here for the sake of example, but in a real application you would cache and reuse
// the prepared statement)
PreparedStatement pst = session.prepare(
insertInto("examples", "json_jackson_function")
.value("id", bindMarker("id"))
.value("user", fromJson(bindMarker("user")))
.value("scores", fromJson(bindMarker("scores"))));
session.execute(pst.bind()
.setInt("id", 2)
.set("user", bob, User.class)
// note that the codec requires that the type passed to the set() method
// be always JsonNode, and not a subclass of it, such as ObjectNode
.set("scores", bobScores, JsonNode.class));
}
// Retrieving JSON payloads from table columns of arbitrary types,
// using toJson() function
private static void selectToJson(Session session) {
Statement stmt = select()
.column("id")
.toJson("user").as("user")
.toJson("scores").as("scores")
.from("examples", "json_jackson_function")
.where(in("id", 1, 2));
ResultSet rows = session.execute(stmt);
for (Row row : rows) {
int id = row.getInt("id");
// retrieve the JSON payload and convert it to a User instance
User user = row.get("user", User.class);
// it is also possible to retrieve the raw JSON payload
String userJson = row.getString("user");
// retrieve the JSON payload and convert it to a JsonNode instance
// note that the codec requires that the type passed to the get() method
// be always JsonNode, and not a subclass of it, such as ObjectNode
JsonNode scores = row.get("scores", JsonNode.class);
// it is also possible to retrieve the raw JSON payload
String scoresJson = row.getString("scores");
System.out.printf("Retrieved row:%n" +
"id %d%n" +
"user %s%n" +
"user (raw) %s%n" +
"scores %s%n" +
"scores (raw) %s%n%n",
id, user, userJson, scores, scoresJson);
}
}
@SuppressWarnings("unused")
public static class User {
private final String name;
private final int age;
@JsonCreator
public User(@JsonProperty("name") String name, @JsonProperty("age") int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return String.format("%s (%s)", name, age);
}
}
}