Java tutorial
/**************************************************************** * Licensed to the Apache Software Foundation (ASF) under one * * or more contributor license agreements. See the NOTICE file * * distributed with this work for additional information * * regarding copyright ownership. The ASF licenses this file * * to you 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 org.apache.james.mailbox.elasticsearch.json; import java.util.Set; import com.fasterxml.jackson.annotation.JsonValue; import com.google.common.base.Joiner; import com.google.common.base.Preconditions; public class Subjects implements Serializable { public static Subjects from(Set<String> subjects) { Preconditions.checkNotNull(subjects, "'subjects' is mandatory"); return new Subjects(subjects); } private final Set<String> subjects; private Subjects(Set<String> subjects) { this.subjects = subjects; } @JsonValue public Set<String> getSubjects() { return subjects; } @Override public String serialize() { return Joiner.on(" ").join(subjects); } }