程序包 org.springframework.messaging.support

类 MessageHeaderAccessor

  • 直接已知子类:
    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 timesteamp headers. Sub-classes 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 sub-classes, 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();
    从以下版本开始:
    4.0
    作者:
    Rossen Stoyanchev, Juergen Hoeller

    • 字段详细资料

    • 构造器详细资料

      • MessageHeaderAccessor

        public MessageHeaderAccessor​(@Nullable
                             Message<?> message)
        A constructor accepting the headers of an existing message to copy.
        参数:
        message - a message to copy the headers from, or null if none

    • 方法详细资料

      • createAccessor

        protected MessageHeaderAccessor createAccessor​(Message<?> message)
        Build a 'nested' accessor for the given message.
        参数:
        message - the message to build a new accessor for
        返回:
        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.

        从以下版本开始:
        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.
        从以下版本开始:
        4.1

      • isMutable

        public boolean isMutable()
        Whether the underlying headers can still be modified.
        从以下版本开始:
        4.1

      • setModified

        protected void setModified​(boolean modified)
        Mark the underlying message headers as modified.
        参数:
        modified - typically true, or false to reset the flag
        从以下版本开始:
        4.1

      • isModified

        public boolean isModified()
        Check whether the underlying message headers have been marked as modified.
        返回:
        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.

        从以下版本开始:
        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.

        从以下版本开始:
        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.
        参数:
        headerName - the name of the header
        返回:
        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.

      • 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".

      • 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.

      • getShortLogMessage

        public String getShortLogMessage​(Object payload)
        Return a concise message for logging purposes.
        参数:
        payload - the payload that corresponds to the headers.
        返回:
        the message

      • getDetailedLogMessage

        public String getDetailedLogMessage​(@Nullable
                                    Object payload)
        Return a more detailed message for logging purposes.
        参数:
        payload - the payload that corresponds to the headers.
        返回:
        the message

      • 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.

        参数:
        message - the message to get an accessor for
        返回:
        an accessor instance of the specified type, or null if none
        从以下版本开始:
        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.

        参数:
        message - the message to get an accessor for
        requiredType - the required accessor type (or null for any)
        返回:
        an accessor instance of the specified type, or null if none
        从以下版本开始:
        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.

        返回:
        an accessor of the required type (never null)
        从以下版本开始:
        4.1