程序包 org.springframework.messaging.support

类 MessageHeaderAccessor

  • 直接已知子类:
    NativeMessageHeaderAccessor
    public class MessageHeaderAccessor
extends Object
    A base for classes providing strongly typed getters and setters as well as behavior around specific categories of headers (e.g. STOMP headers). Supports creating new headers, modifying existing headers (when still mutable), or copying and modifying existing headers.

    The method getMessageHeaders() provides access to the underlying, fully-prepared MessageHeaders that can then be used as-is (i.e. without copying) to create a single message as follows: 

     MessageHeaderAccessor accessor = new MessageHeaderAccessor();
 accessor.setHeader("foo", "bar");
 Message message = MessageBuilder.createMessage("payload", accessor.getMessageHeaders());

    After the above, by default the MessageHeaderAccessor becomes immutable. However it is possible to leave it mutable for further initialization in the same thread, for example: 

     MessageHeaderAccessor accessor = new MessageHeaderAccessor();
 accessor.setHeader("foo", "bar");
 accessor.setLeaveMutable(true);
 Message message = MessageBuilder.createMessage("payload", accessor.getMessageHeaders());

 // later on in the same thread...

 MessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message);
 accessor.setHeader("bar", "baz");
 accessor.setImmutable();

    The method toMap() returns a copy of the underlying headers. It can be used to prepare multiple messages from the same MessageHeaderAccessor instance: 

     MessageHeaderAccessor accessor = new MessageHeaderAccessor();
 MessageBuilder builder = MessageBuilder.withPayload("payload").setHeaders(accessor);

 accessor.setHeader("foo", "bar1");
 Message message1 = builder.build();

 accessor.setHeader("foo", "bar2");
 Message message2 = builder.build();

 accessor.setHeader("foo", "bar3");
 Message  message3 = builder.build();

    However note that with the above style, the header accessor is shared and cannot be re-obtained later on. Alternatively it is also possible to create one MessageHeaderAccessor per message: 

     MessageHeaderAccessor accessor1 = new MessageHeaderAccessor();
 accessor.set("foo", "bar1");
 Message message1 = MessageBuilder.createMessage("payload", accessor1.getMessageHeaders());

 MessageHeaderAccessor accessor2 = new MessageHeaderAccessor();
 accessor.set("foo", "bar2");
 Message message2 = MessageBuilder.createMessage("payload", accessor2.getMessageHeaders());

 MessageHeaderAccessor accessor3 = new MessageHeaderAccessor();
 accessor.set("foo", "bar3");
 Message message3 = MessageBuilder.createMessage("payload", accessor3.getMessageHeaders());

    Note that the above examples aim to demonstrate the general idea of using header accessors. The most likely usage however is through subclasses.

    从以下版本开始:
    4.0
    作者:
    Rossen Stoyanchev, Juergen Hoeller

    • 构造器详细资料

      • MessageHeaderAccessor

        public MessageHeaderAccessor​(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

        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,
                      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".

      • copyHeaders

        public void copyHeaders​(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​(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​(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

        public 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.

        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

      • getAccessor

        public 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.

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

        参数:
        messageHeaders - the message headers 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