/*
* 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 static com.datastax.driver.core.querybuilder.QueryBuilder.*;
/**
* Illustrates how to map a single table column of type {@code VARCHAR},
* containing JSON payloads, into a Java object using
* the <a href="http://wiki.fasterxml.com/JacksonHome">Jackson</a> library.
* <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 table "examples.json_jackson_column". If it already exists, it will be reused;
* - inserts data in the table.
*/
public class JacksonJsonColumn {
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);
cluster = Cluster.builder()
.addContactPoints(CONTACT_POINTS).withPort(PORT)
.withCodecRegistry(new CodecRegistry().register(userCodec))
.build();
Session session = cluster.connect();
createSchema(session);
insertJsonColumn(session);
selectJsonColumn(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 TABLE IF NOT EXISTS examples.json_jackson_column(" +
"id int PRIMARY KEY, json text)");
}
// Mapping a User instance to a table column
private static void insertJsonColumn(Session session) {
User alice = new User("alice", 30);
User bob = new User("bob", 35);
// Build and execute a simple statement
Statement stmt = insertInto("examples", "json_jackson_column")
.value("id", 1)
// the User object will be converted into a String and persisted into the VARCHAR column "json"
.value("json", alice);
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_column")
.value("id", bindMarker("id"))
.value("json", bindMarker("json")));
session.execute(pst.bind()
.setInt("id", 2)
.set("json", bob, User.class));
}
// Retrieving User instances from a table column
private static void selectJsonColumn(Session session) {
Statement stmt = select()
.from("examples", "json_jackson_column")
.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("json", User.class);
// it is also possible to retrieve the raw JSON payload
String json = row.getString("json");
System.out.printf("Retrieved row:%n" +
"id %d%n" +
"user %s%n" +
"user (raw) %s%n%n",
id, user, json);
}
}
@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);
}
}
}