/*
* Copyright 2002-2016 the original author or authors.
*
* 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 org.springframework.messaging;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.UUID;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.util.AlternativeJdkIdGenerator;
import org.springframework.util.IdGenerator;
/**
* The headers for a {@link Message}.
*
* <p><b>IMPORTANT</b>: This class is immutable. Any mutating operation such as
* {@code put(..)}, {@code putAll(..)} and others will throw
* {@link UnsupportedOperationException}.
* <p>Subclasses do have access to the raw headers, however, via {@link #getRawHeaders()}.
*
* <p>One way to create message headers is to use the
* {@link org.springframework.messaging.support.MessageBuilder MessageBuilder}:
* <pre class="code">
* MessageBuilder.withPayload("foo").setHeader("key1", "value1").setHeader("key2", "value2");
* </pre>
*
* A second option is to create {@link org.springframework.messaging.support.GenericMessage}
* passing a payload as {@link Object} and headers as a {@link Map java.util.Map}:
* <pre class="code">
* Map headers = new HashMap();
* headers.put("key1", "value1");
* headers.put("key2", "value2");
* new GenericMessage("foo", headers);
* </pre>
*
* A third option is to use {@link org.springframework.messaging.support.MessageHeaderAccessor}
* or one of its subclasses to create specific categories of headers.
*
* @author Arjen Poutsma
* @author Mark Fisher
* @author Gary Russell
* @author Juergen Hoeller
* @since 4.0
* @see org.springframework.messaging.support.MessageBuilder
* @see org.springframework.messaging.support.MessageHeaderAccessor
*/
public class MessageHeaders implements Map<String, Object>, Serializable {
public static final UUID ID_VALUE_NONE = new UUID(0,0);
/**
* The key for the Message ID. This is an automatically generated UUID and
* should never be explicitly set in the header map <b>except</b> in the
* case of Message deserialization where the serialized Message's generated
* UUID is being restored.
*/
public static final String ID = "id";
public static final String TIMESTAMP = "timestamp";
public static final String CONTENT_TYPE = "contentType";
public static final String REPLY_CHANNEL = "replyChannel";
public static final String ERROR_CHANNEL = "errorChannel";
private static final long serialVersionUID = 7035068984263400920L;
private static final Log logger = LogFactory.getLog(MessageHeaders.class);
private static final IdGenerator defaultIdGenerator = new AlternativeJdkIdGenerator();
private static volatile IdGenerator idGenerator = null;
private final Map<String, Object> headers;
/**
* Construct a {@link MessageHeaders} with the given headers. An {@link #ID} and
* {@link #TIMESTAMP} headers will also be added, overriding any existing values.
* @param headers a map with headers to add
*/
public MessageHeaders(Map<String, Object> headers) {
this(headers, null, null);
}
/**
* Constructor providing control over the ID and TIMESTAMP header values.
* @param headers a map with headers to add
* @param id the {@link #ID} header value
* @param timestamp the {@link #TIMESTAMP} header value
*/
protected MessageHeaders(Map<String, Object> headers, UUID id, Long timestamp) {
this.headers = (headers != null ? new HashMap<>(headers) : new HashMap<String, Object>());
if (id == null) {
this.headers.put(ID, getIdGenerator().generateId());
}
else if (id == ID_VALUE_NONE) {
this.headers.remove(ID);
}
else {
this.headers.put(ID, id);
}
if (timestamp == null) {
this.headers.put(TIMESTAMP, System.currentTimeMillis());
}
else if (timestamp < 0) {
this.headers.remove(TIMESTAMP);
}
else {
this.headers.put(TIMESTAMP, timestamp);
}
}
/**
* Copy constructor which allows for ignoring certain entries.
* Used for serialization without non-serializable entries.
* @param original the MessageHeaders to copy
* @param keysToIgnore the keys of the entries to ignore
*/
private MessageHeaders(MessageHeaders original, Set<String> keysToIgnore) {
this.headers = new HashMap<>(original.headers.size() - keysToIgnore.size());
for (Map.Entry<String, Object> entry : original.headers.entrySet()) {
if (!keysToIgnore.contains(entry.getKey())) {
this.headers.put(entry.getKey(), entry.getValue());
}
}
}
protected Map<String, Object> getRawHeaders() {
return this.headers;
}
protected static IdGenerator getIdGenerator() {
return (idGenerator != null ? idGenerator : defaultIdGenerator);
}
public UUID getId() {
return get(ID, UUID.class);
}
public Long getTimestamp() {
return get(TIMESTAMP, Long.class);
}
public Object getReplyChannel() {
return get(REPLY_CHANNEL);
}
public Object getErrorChannel() {
return get(ERROR_CHANNEL);
}
@SuppressWarnings("unchecked")
public <T> T get(Object key, Class<T> type) {
Object value = this.headers.get(key);
if (value == null) {
return null;
}
if (!type.isAssignableFrom(value.getClass())) {
throw new IllegalArgumentException("Incorrect type specified for header '" +
key + "'. Expected [" + type + "] but actual type is [" + value.getClass() + "]");
}
return (T) value;
}
// Delegating Map implementation
public boolean containsKey(Object key) {
return this.headers.containsKey(key);
}
public boolean containsValue(Object value) {
return this.headers.containsValue(value);
}
public Set<Map.Entry<String, Object>> entrySet() {
return Collections.unmodifiableMap(this.headers).entrySet();
}
public Object get(Object key) {
return this.headers.get(key);
}
public boolean isEmpty() {
return this.headers.isEmpty();
}
public Set<String> keySet() {
return Collections.unmodifiableSet(this.headers.keySet());
}
public int size() {
return this.headers.size();
}
public Collection<Object> values() {
return Collections.unmodifiableCollection(this.headers.values());
}
// Unsupported Map operations
/**
* Since MessageHeaders are immutable, the call to this method
* will result in {@link UnsupportedOperationException}.
*/
public Object put(String key, Object value) {
throw new UnsupportedOperationException("MessageHeaders is immutable");
}
/**
* Since MessageHeaders are immutable, the call to this method
* will result in {@link UnsupportedOperationException}.
*/
public void putAll(Map<? extends String, ? extends Object> map) {
throw new UnsupportedOperationException("MessageHeaders is immutable");
}
/**
* Since MessageHeaders are immutable, the call to this method
* will result in {@link UnsupportedOperationException}.
*/
public Object remove(Object key) {
throw new UnsupportedOperationException("MessageHeaders is immutable");
}
/**
* Since MessageHeaders are immutable, the call to this method
* will result in {@link UnsupportedOperationException}.
*/
public void clear() {
throw new UnsupportedOperationException("MessageHeaders is immutable");
}
// Serialization methods
private void writeObject(ObjectOutputStream out) throws IOException {
Set<String> keysToIgnore = new HashSet<>();
for (Map.Entry<String, Object> entry : this.headers.entrySet()) {
if (!(entry.getValue() instanceof Serializable)) {
keysToIgnore.add(entry.getKey());
}
}
if (keysToIgnore.isEmpty()) {
// All entries are serializable -> serialize the regular MessageHeaders instance
out.defaultWriteObject();
}
else {
// Some non-serializable entries -> serialize a temporary MessageHeaders copy
if (logger.isDebugEnabled()) {
logger.debug("Ignoring non-serializable message headers: " + keysToIgnore);
}
out.writeObject(new MessageHeaders(this, keysToIgnore));
}
}
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
}
// equals, hashCode, toString
@Override
public boolean equals(Object other) {
return (this == other ||
(other instanceof MessageHeaders && this.headers.equals(((MessageHeaders) other).headers)));
}
@Override
public int hashCode() {
return this.headers.hashCode();
}
@Override
public String toString() {
return this.headers.toString();
}
}