org.springframework.messaging.support

Class MessageHeaderAccessor

java.lang.Object

org.springframework.messaging.support.MessageHeaderAccessor

Direct Known Subclasses:

NativeMessageHeaderAccessor

public class MessageHeaderAccessor
extends Object

Wrapper around MessageHeaders that provides extra features such as strongly typed accessors for specific headers, the ability to leave headers in a Message mutable, and the option to suppress automatic generation of id and timestamp headers. Subclasses such as NativeMessageHeaderAccessor and others provide support for managing processing vs external source headers as well as protocol specific headers.

Below is a workflow to initialize headers via MessageHeaderAccessor, or one of its subclasses, then create a Message, and then re-obtain the accessor possibly from a different component:

 // Create a message with headers
 MessageHeaderAccessor accessor = new MessageHeaderAccessor();
 accessor.setHeader("foo", "bar");
 MessageHeaders headers = accessor.getMessageHeaders();
 Message message = MessageBuilder.createMessage("payload", headers);

 // Later on
 MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message);
 Assert.notNull(accessor, "No MessageHeaderAccessor");
 

In order for the above to work, all participating components must use MessageHeaders to create, access, or modify headers, or otherwise getAccessor(Message, Class) will return null. Below is a workflow that shows how headers are created and left mutable, then modified possibly by a different component, and finally made immutable perhaps before the possibility of being accessed on a different thread:

 // Create a message with mutable headers
 MessageHeaderAccessor accessor = new MessageHeaderAccessor();
 accessor.setHeader("foo", "bar");
 accessor.setLeaveMutable(true);
 MessageHeaders headers = accessor.getMessageHeaders();
 Message message = MessageBuilder.createMessage("payload", headers);

 // Later on
 MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message);
 if (accessor.isMutable()) {
     // It's mutable, just change the headers
     accessor.setHeader("bar", "baz");
 }
 else {
     // It's not, so get a mutable copy, change and re-create
     accessor = MessageHeaderAccessor.getMutableAccessor(message);
     accessor.setHeader("bar", "baz");
     accessor.setLeaveMutable(true); // leave mutable again or not?
     message = MessageBuilder.createMessage(message.getPayload(), accessor);
 }

 // Make the accessor immutable
 MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message);
 accessor.setImmutable();
 

Since:

4.0

Author:

Rossen Stoyanchev, Juergen Hoeller

Field Summary

Fields

Modifier and Type	Field and Description
static Charset	DEFAULT_CHARSET The default charset used for headers.

Constructor Summary

Constructors

Constructor and Description
MessageHeaderAccessor() A constructor to create new headers.
MessageHeaderAccessor(Message<?> message) A constructor accepting the headers of an existing message to copy.

Method Summary

Modifier and Type	Method and Description
void	copyHeaders(Map<String,?> headersToCopy) Copy the name-value pairs from the provided Map.
void	copyHeadersIfAbsent(Map<String,?> headersToCopy) Copy the name-value pairs from the provided Map.
protected MessageHeaderAccessor	createAccessor(Message<?> message) Build a 'nested' accessor for the given message.
static MessageHeaderAccessor	getAccessor(Message<?> message) Return the original MessageHeaderAccessor used to create the headers of the given Message, or null if that's not available or if its type does not match the required type.
static <T extends MessageHeaderAccessor> T	getAccessor(Message<?> message, Class<T> requiredType) Return the original MessageHeaderAccessor used to create the headers of the given Message, or null if that's not available or if its type does not match the required type.
static <T extends MessageHeaderAccessor> T	getAccessor(MessageHeaders messageHeaders, Class<T> requiredType) A variation of getAccessor(org.springframework.messaging.Message, Class) with a MessageHeaders instance instead of a Message.
MimeType	getContentType()
String	getDetailedLogMessage(Object payload) Return a more detailed message for logging purposes.
protected String	getDetailedPayloadLogMessage(Object payload)
Object	getErrorChannel()
Object	getHeader(String headerName) Retrieve the value for the header with the given name.
UUID	getId()
MessageHeaders	getMessageHeaders() Return the underlying MessageHeaders instance.
static MessageHeaderAccessor	getMutableAccessor(Message<?> message) Return a mutable MessageHeaderAccessor for the given message attempting to match the type of accessor used to create the message headers, or otherwise wrapping the message with a MessageHeaderAccessor instance.
Object	getReplyChannel()
String	getShortLogMessage(Object payload) Return a concise message for logging purposes.
protected String	getShortPayloadLogMessage(Object payload)
Long	getTimestamp()
boolean	isModified() Check whether the underlying message headers have been marked as modified.
boolean	isMutable() Whether the underlying headers can still be modified.
protected boolean	isReadableContentType()
protected boolean	isReadOnly(String headerName)
void	removeHeader(String headerName) Remove the value for the given header name.
void	removeHeaders(String... headerPatterns) Removes all headers provided via array of 'headerPatterns'.
void	setContentType(MimeType contentType)
void	setErrorChannel(MessageChannel errorChannel)
void	setErrorChannelName(String errorChannelName)
void	setHeader(String name, Object value) Set the value for the given header name.
void	setHeaderIfAbsent(String name, Object value) Set the value for the given header name only if the header name is not already associated with a value.
void	setImmutable() By default, when getMessageHeaders() is called, "this" MessageHeaderAccessor instance can no longer be used to modify the underlying message headers.
void	setLeaveMutable(boolean leaveMutable) By default, when getMessageHeaders() is called, "this" MessageHeaderAccessor instance can no longer be used to modify the underlying message headers and the returned MessageHeaders is immutable.
protected void	setModified(boolean modified) Mark the underlying message headers as modified.
void	setReplyChannel(MessageChannel replyChannel)
void	setReplyChannelName(String replyChannelName)
Map<String,Object>	toMap() Return a copy of the underlying header values as a plain Map object.
MessageHeaders	toMessageHeaders() Return a copy of the underlying header values as a MessageHeaders object.
String	toString()
protected void	verifyType(String headerName, Object headerValue)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_CHARSET

public static final Charset DEFAULT_CHARSET

The default charset used for headers.

Constructor Detail

MessageHeaderAccessor

public MessageHeaderAccessor()

A constructor to create new headers.

MessageHeaderAccessor

public MessageHeaderAccessor(@Nullable
                             Message<?> message)

A constructor accepting the headers of an existing message to copy.

Parameters:

message - a message to copy the headers from, or null if none

Method Detail

createAccessor

protected MessageHeaderAccessor createAccessor(Message<?> message)

Build a 'nested' accessor for the given message.

Parameters:

message - the message to build a new accessor for

Returns:

the nested accessor (typically a specific subclass)

setLeaveMutable

public void setLeaveMutable(boolean leaveMutable)

By default, when getMessageHeaders() is called, "this" MessageHeaderAccessor instance can no longer be used to modify the underlying message headers and the returned MessageHeaders is immutable.

However when this is set to true, the returned (underlying) MessageHeaders instance remains mutable. To make further modifications continue to use the same accessor instance or re-obtain it via:
MessageHeaderAccessor.getAccessor(Message, Class)

When modifications are complete use setImmutable() to prevent further changes. The intended use case for this mechanism is initialization of a Message within a single thread.

By default this is set to false.

Since:

4.1

setImmutable

public void setImmutable()

By default, when getMessageHeaders() is called, "this" MessageHeaderAccessor instance can no longer be used to modify the underlying message headers. However if setLeaveMutable(boolean) is used, this method is necessary to indicate explicitly when the MessageHeaders instance should no longer be modified.

Since:

4.1

isMutable

public boolean isMutable()

Whether the underlying headers can still be modified.

Since:

4.1

setModified

protected void setModified(boolean modified)

Mark the underlying message headers as modified.

Parameters:

modified - typically true, or false to reset the flag

Since:

4.1

isModified

public boolean isModified()

Check whether the underlying message headers have been marked as modified.

Returns:

true if the flag has been set, false otherwise

getMessageHeaders

public MessageHeaders getMessageHeaders()

Return the underlying MessageHeaders instance.

Unless setLeaveMutable(boolean) was set to true, after this call, the headers are immutable and this accessor can no longer modify them.

This method always returns the same MessageHeaders instance if invoked multiples times. To obtain a copy of the underlying headers, use toMessageHeaders() or toMap() instead.

Since:

4.1

toMessageHeaders

public MessageHeaders toMessageHeaders()

Return a copy of the underlying header values as a MessageHeaders object.

This method can be invoked many times, with modifications in between where each new call returns a fresh copy of the current header values.

Since:

4.1

toMap

public Map<String,Object> toMap()

Return a copy of the underlying header values as a plain Map object.

This method can be invoked many times, with modifications in between where each new call returns a fresh copy of the current header values.

getHeader

@Nullable
public Object getHeader(String headerName)

Retrieve the value for the header with the given name.

Parameters:

headerName - the name of the header

Returns:

the associated value, or null if none found

setHeader

public void setHeader(String name,
                      @Nullable
                      Object value)

Set the value for the given header name.

If the provided value is null, the header will be removed.

verifyType

protected void verifyType(@Nullable
                          String headerName,
                          @Nullable
                          Object headerValue)

setHeaderIfAbsent

public void setHeaderIfAbsent(String name,
                              Object value)

Set the value for the given header name only if the header name is not already associated with a value.

removeHeader

public void removeHeader(String headerName)

Remove the value for the given header name.

removeHeaders

public void removeHeaders(String... headerPatterns)

Removes all headers provided via array of 'headerPatterns'.

As the name suggests, array may contain simple matching patterns for header names. Supported pattern styles are: "xxx*", "*xxx", "*xxx*" and "xxx*yyy".

copyHeaders

public void copyHeaders(@Nullable
                        Map<String,?> headersToCopy)

Copy the name-value pairs from the provided Map.

This operation will overwrite any existing values. Use copyHeadersIfAbsent(Map) to avoid overwriting values.

copyHeadersIfAbsent

public void copyHeadersIfAbsent(@Nullable
                                Map<String,?> headersToCopy)

Copy the name-value pairs from the provided Map.

This operation will not overwrite any existing values.

isReadOnly

protected boolean isReadOnly(String headerName)

getId

@Nullable
public UUID getId()

getTimestamp

@Nullable
public Long getTimestamp()

setContentType

public void setContentType(MimeType contentType)

getContentType

@Nullable
public MimeType getContentType()

setReplyChannelName

public void setReplyChannelName(String replyChannelName)

setReplyChannel

public void setReplyChannel(MessageChannel replyChannel)

getReplyChannel

@Nullable
public Object getReplyChannel()

setErrorChannelName

public void setErrorChannelName(String errorChannelName)

setErrorChannel

public void setErrorChannel(MessageChannel errorChannel)

getErrorChannel

@Nullable
public Object getErrorChannel()

getShortLogMessage

public String getShortLogMessage(Object payload)

Return a concise message for logging purposes.

Parameters:

payload - the payload that corresponds to the headers.

Returns:

the message

getDetailedLogMessage

public String getDetailedLogMessage(@Nullable
                                    Object payload)

Return a more detailed message for logging purposes.

Parameters:

payload - the payload that corresponds to the headers.

Returns:

the message

getShortPayloadLogMessage

protected String getShortPayloadLogMessage(Object payload)

getDetailedPayloadLogMessage

protected String getDetailedPayloadLogMessage(@Nullable
                                              Object payload)

isReadableContentType

protected boolean isReadableContentType()

toString

public String toString()

Overrides:

toString in class Object

getAccessor

@Nullable
public static MessageHeaderAccessor getAccessor(Message<?> message)

Return the original MessageHeaderAccessor used to create the headers of the given Message, or null if that's not available or if its type does not match the required type.

This is for cases where the existence of an accessor is strongly expected (followed up with an assertion) or where an accessor will be created otherwise.

Parameters:

message - the message to get an accessor for

Returns:

an accessor instance of the specified type, or null if none

Since:

5.1.19

getAccessor

@Nullable
public static <T extends MessageHeaderAccessor> T getAccessor(Message<?> message,
                                                                        @Nullable
                                                                        Class<T> requiredType)

Return the original MessageHeaderAccessor used to create the headers of the given Message, or null if that's not available or if its type does not match the required type.

This is for cases where the existence of an accessor is strongly expected (followed up with an assertion) or where an accessor will be created otherwise.

Parameters:

message - the message to get an accessor for

requiredType - the required accessor type (or null for any)

Returns:

an accessor instance of the specified type, or null if none

Since:

4.1

getAccessor

@Nullable
public static <T extends MessageHeaderAccessor> T getAccessor(MessageHeaders messageHeaders,
                                                                        @Nullable
                                                                        Class<T> requiredType)

A variation of getAccessor(org.springframework.messaging.Message, Class) with a MessageHeaders instance instead of a Message.

This is for cases when a full message may not have been created yet.

Parameters:

messageHeaders - the message headers to get an accessor for

requiredType - the required accessor type (or null for any)

Returns:

an accessor instance of the specified type, or null if none

Since:

4.1

getMutableAccessor

public static MessageHeaderAccessor getMutableAccessor(Message<?> message)

Return a mutable MessageHeaderAccessor for the given message attempting to match the type of accessor used to create the message headers, or otherwise wrapping the message with a MessageHeaderAccessor instance.

This is for cases where a header needs to be updated in generic code while preserving the accessor type for downstream processing.

Returns:

an accessor of the required type (never null)

Since:

4.1