The Synapse project has developed a set of transport implementations that provide protocol support and/or features that go beyond what is provided out of the box by Axis2:

  • A non blocking HTTP transport that gives better performance in a highly asynchronous environment like Synapse.
  • A VFS transport that can read messages from files and write outgoing messages to a file system. The file system can be local or remote, and several remote protocols are supported, such as FTP, SSH, WebDAV, etc.
  • A transport supporting the Financial Information eXchange protocol. FIX is a public-domain messaging standard developed specifically for the real-time electronic exchange of securities transactions. It has a large user base and is developed by the collaborative effort of banks, broker-dealers, exchanges, industry utilities and associations, institutional investors, and IT providers around the world.

Note that while these transports are developed as part of the Synapse project, they can be used with any Axis2 based application.

The Synapse distribution also comes bundled with the following transports from the Axis2 Transport project:

  • A JMS transport supporting any JMS 1.0 or 1.1 provider.
  • A Mail transport able to send messages using SMTP and poll messages from a POP3 or IMAP account.

    Apache Synapse is also compatible with the following transport implementations from the Apache Axis2 Transports project:

  • TCP transport
  • SMS transport
  • UDP transport
  • XMPP transport

    These transports are not shipped with Apache Synapse by default and hence they should be downloaded separately from the Axis2 transport website and installed in the Synapse runtime.

Non-blocking HTTP transport

Example configurations

<transportReceiver name="http" class="org.apache.synapse.transport.nhttp.HttpCoreNIOListener">
    <parameter name="port">8280</parameter>
    <parameter name="non-blocking">true</parameter>

<transportReceiver name="https" class="org.apache.synapse.transport.nhttp.HttpCoreNIOSSLListener">
    <parameter name="port" locked="false">8243</parameter>
    <parameter name="non-blocking" locked="false">true</parameter>
    <parameter name="keystore" locked="false">
    <parameter name="truststore" locked="false">

<transportSender name="http"  class="org.apache.synapse.transport.nhttp.HttpCoreNIOSender">
    <parameter name="non-blocking" locked="false">true</parameter>
    <parameter name="warnOnHTTP500" locked="false">*</parameter>

<transportSender name="https" class="org.apache.synapse.transport.nhttp.HttpCoreNIOSSLSender">
    <parameter name="non-blocking" locked="false">true</parameter>
    <parameter name="warnOnHTTP500" locked="false">*</parameter>
    <parameter name="keystore" locked="false">
    <parameter name="truststore" locked="false">

Transport listener parameters

The following parameters are supported by both the HTTP and the HTTPS listener:

The TCP port to bind the listener to.
The IP address to bind the listener to. This can be used on hosts that have more than one network interface or IP address to run multiple Synapse instances listening to the same port. If this parameter is not specified, the listener will accept connections on any IP address.
The host name to use when computing endpoint references in generated WSDL files. The default value is the host name as provided by the operation system or localhost if the host name can't be determined. The value of this parameter is ignored if WSDLEPRPrefix is specified.
The URL prefix to use when computing endpoint references in generated WSDL files. The value must be a valid URL with at least a protocol and host. If this value is unspecified, endpoint references will be computed based on the listener type (HTTP or HTTPS) and hostname and port parameters.

This parameter should be used if clients connect to Synapse through a frontend server, e.g. a (load balancing) Apache, and these clients rely on the address information in the WSDL documents exposed through ...?wsdl URLs.

The following parameters are specific to the HTTPS listener:

The keystore configuration. The value of this parameter must be a <KeyStore> element as shown in the example configurations above.
The truststore configuration. The value of this parameter must be a <TrustStore> element as shown in the example configurations above.
This parameter has the same meaning as the corresponding mod_ssl directive and sets the desired certificate verification level for client authentication:
  • none (default): no client certificate is required at all
  • optional : the client may present a valid certificate, but is not required to do so
  • require : the client has to present a valid certificate, otherwise the connection request will be terminated during SSL handshake

Transport sender parameters

The following property can be used to control based on content-types whether the HTTP/HTTPS sender shall output a warning for responses with HTTP status code 500.

A list of content-types for which Synapse shall output a warning when receiving an HTTP 500 response (each value each seperated by a |). By default Synapse outputs a warning for any HTTP 500 response, irrespective of the content-type. Consequently, also for each SOAP fault a warning will be logged. If only for specific content-types a warning shall be logged, please provide a |-separated list. To output the warning for messages which do not have a content-type set, please use the value "none"!

Example value: x-application/hessian|none

The following properties can be used to configure the HTTP sender to use a proxy. They can be specified either as transport parameters in declared in <transportSender> or as system properties.

The host name or address of the proxy server.
The TCP port of the proxy server.
The hosts to which the HTTP sender should connect directly and not through the proxy server. The value can be a list of hosts, each seperated by a |, and in addition a wildcard character (*) can be used for matching.

Example value: *|localhost

Note that the HTTPS sender has no proxy support yet.

The following parameters are specific to the HTTP sender:

The keystore configuration. The value of this parameter must be a <KeyStore> element as shown in the example configurations above.
The truststore configuration. The value of this parameter must be a <TrustStore> element as shown in the example configurations above.
When set to true , this parameter disables server certificate validation (trust). The default value is false . This parameter will be ignored if truststore is set.

Setting his parameter to true is useful in development and test environments, but should not be used in production environments. If validation is disabled, a warning message will be logged at startup.

This optional parameter specifies the policy to apply when checking that the hostname of the server matches the names stored inside the X.509 certificate presented by the server. Possible values are Strict , AllowAll and DefaultAndLocalhost . See the HostnameVerifier Javadoc for more details.

VFS transport

Transport listener

The VFS transport listener receives messages dropped in a given local or remote file system location. The location is specified by a URL that either identifies a single file or a directory. The transport listener will periodically poll the specified location and process any file(s) found. After a file has been processed it will be deleted or moved to another location. Note that this is absolutely mandatory to prevent the listener from processing files multiple times. Therefore the VFS transport listener can only be used in situations where it has write access to the file system location and where deleting or moving the dropped files is acceptable.

The transport is based on Apache Commons VFS and supports any protocol for which a VFS provider is available. The transport is preconfigured with providers for local files (file: scheme), HTTP, HTTPS, FTP and SFTP (i.e. file transfer over SSH).

There is a fundamental difference between the VFS transport and transports such as HTTP and it is important to understand this difference to be able to use the VFS transport correctly. The HTTP transport binds to a single protocol endpoint, i.e. a TCP port on which it accepts incoming HTTP requests. These requests are then dispatched to the right service based on the request URI. On the other hand, the VFS transport only receives the payload of a message, but no additional information that could be used to dispatch the message to a service. This means that file system locations must be explicitly mapped to services. This is done using a set of service parameters.

For Synapse this means that the VFS transport listener can only be used in conjunction with proxy services. The relevant service parameters are then specified as follows:

<proxy name="MyVFSService" transports="vfs">
    <parameter name="transport.vfs.FileURI">file:///var/spool/synapse/in</parameter>
    <parameter name="transport.vfs.ContentType">application/xml</parameter>

In this example the file system location file:///var/spool/synapse/in is explicitly bound to MyVFSService , i.e. any message dropped in that location will be predispatched to that service, bypassing any other configured dispatch mechanisms that would apply to messages received through HTTP.

The VFS transport recognizes the following service parameters:

transport.vfs.FileURI (Required)
The primary File (or Directory) URI in the vfs* transport format, for this service
transport.vfs.ContentType (Required)
The expected content type for files retrieved for this service. The VFS transport uses this information to select the appropriate message builder.


  • text/xml for plain XML or SOAP
  • text/plain; charset=ISO-8859-1 for text files
  • application/octet-stream for binary data
transport.vfs.FileNamePattern (Optional)
A file name regex pattern to match files against a directory specified by the FileURI
transport.PollInterval (Optional)
The poll interval (in seconds)
transport.vfs.ActionAfterProcess (Optional)
transport.vfs.MoveAfterProcess (Optional)
The directory to move files after processing (i.e. all files process successfully)
transport.vfs.ActionAfterErrors (Optional)
transport.vfs.MoveAfterErrors (Optional)
The directory to move files after errors (i.e. some of the files succeed but some fail)
transport.vfs.ActionAfterFailure (Optional)
transport.vfs.MoveAfterFailure (Optional)
The directory to move after failure (i.e. all files fail)
transport.vfs.ReplyFileURI (Optional)
Reply file URI
transport.vfs.ReplyFileName (Optional)
Reply file name (defaults to response.xml)
transport.vfs.MoveTimestampFormat (Optional)
Timestamp prefix format for processed file name. java.text.SimpleDateFormat compatible string. e.g. yyMMddHHmmss'-'
transport.vfs.Locking (Optional)
By-default file locking is turned on in the VFS transport, and this parameter lets you configure the locking behaviour on a per service basis. Possible values are enable or disable , and both these values are important because the locking can be disabled at the global level by specifying that at the receiver level and selectively enable locking only for a set of services.
transport.vfs.Streaming (Optional)
If this parameter is set to true , the transport will attempt to use a javax.activation.DataSource (instead of a ) object to pass the content of the file to the message builder. Note that this is only supported by some message builders, e.g. for plain text and binary.

This allows processing of the message without storing the entire content in memory. It also has two other side effects:

  • The incoming file (or connection in case of a remote file) will only be opened on demand.
  • Since the data is not cached, the file might be read several times.

This option can be used to achieve streaming of large payloads. Note that this feature is still somewhat experimental and might be superseded by a more flexible mechanism in a future release.

Note that since the VFS endpoints are configured at the level of the service, the only parameter that is available at the listener is the file locking configuration parameter whcih is optional and the transport listener is enabled in axis2.xml simply as follows:

<transportReceiver name="vfs" class="org.apache.synapse.transport.vfs.VFSTransportListener">
    <parameter name="transport.vfs.Locking">enable | disable</parameter> ?

Transport sender

The VFS transport sender allows to write outgoing messages to local or remote files. As with the listener, the transport sender supports any protocol for which there is a VFS provider.

The sender is enabled be the following directive in axis2.xml file locking which is by-default enabled can be configured using the transport.vfs.Locking parameter:

<transportSender name="vfs" class="org.apache.synapse.transport.vfs.VFSTransportSender">
    <parameter name="transport.vfs.Locking">enable | disable</parameter> ?

To send a message using the VFS transport, the destination URI must start with vfs: followed by a valid VFS URL. For example, in a Synapse mediation, one would use:

    <address uri="vfs:file:///var/spool/synapse/out"/>

Other examples of valid VFS URLs are (see for more samples):

  • file:///directory/filename.ext
  • file:////somehost/someshare/afile.txt
  • jar:../lib/classes.jar!/META-INF/
  • ftp://myusername:mypassword@somehost/pub/downloads/somefile.tgz[?vfs.passive=true]

The global configuration of the file locking can be overriden by providing the transport.vfs.Locking as a URL parameter with the appropriate value (enable , or disable ) on a given endpoint.

It should be noted that by its nature, the VFS transport sender doesn't support synchronous responses and should only be invoked using the out-only message exchange pattern. In a Synapse mediation, this can be forced using the following mediator:

<property action="set" name="OUT_ONLY" value="true"/>

Using SFTP

To avoid man-in-the-middle attacks, SSH clients will only connect to hosts with a known host key. When connecting for the first time to an SSH server, a typical command line SSH client would request confirmation from the user to add the server and its fingerprint to the list of known hosts.

The VFS transports supports SFTP through the JSch library and this library also requires a list of known hosts. Since Synapse is not an interactive process, it can't request confirmation from the user and is therefore unable to automatically add a host to the list. This implies that the list of known hosts must be set up manually before the transport can connect.

Jsch loads the list of known hosts from a file called known_hosts in the .ssh subdirectory of the user's home directory, i.e. $HOME/.ssh in Unix and %HOMEPATH%\.ssh in Windows. The location and format of this file are compatible with the OpenSSH client.

Since the file not only contains a list of hostnames but also the fingerprints of their host keys, the easiest way to add a new host to that file is to simply use the OpenSSH client to open an SSH session on the target host. The client will then ask to add the credentials to the known_hosts file. Note that if the SSH server is configured to only allow SFTP sessions, but no interactive sessions, the connection will actually fail. Since this doesn't rollback the change to the known_hosts file, this error can be ignored.

Known issues

The VFS listener will start reading a file as soon as it appears in the configured location. To avoid processing half written files, the creation of these files should be made atomic. On most platforms this can be achieved by writing the data to a temporary file and then moving the file to the target location. Note however that a move operation is only atomic if the source and destination are on the same physical file system. The location for the temporary file should be chosen with that constraint in mind.

It should also be noted that the VFS transport sender doesn't create files atomically.

FIX transport

A general overview about the FIX transport can be found in the following articles:

Setting up the FIX Transport

To use the FIX transport, you need a local Quickfix/J installation. Download Quickfix/J from .

To enable the FIX transport, you need to uncomment the FIX transport sender and FIX transport receiver configurations in the SYNAPSE_HOME/repository/conf/axis2.xml. Simply locate and uncomment the FIXTransportSender and FIXTransportListener sample configurations. Also add the following jars to the Synapse class path (SYNAPSE_HOME/lib directory).

  • quickfixj-core.jar
  • quickfixj-msg-fix40.jar
  • quickfixj-msg-fix41.jar
  • quickfixj-msg-fix42.jar
  • quickfixj-msg-fix43.jar
  • quickfixj-msg-fix44.jar
  • mina-core-1.1.0.jar
  • slf4j-api-1.3.0.jar
  • slf4j-jdk14-1.3.0.jar

All these jars are shipped with the Quickfix/J binary distribution.

FIX Transport Parameters

This is the list of all parameters accepted by the FIX transport. Refer the sample 257 and 258 to see how some of them are used in practice.

If a service needs to listen to incoming FIX messages from a remote initiator then Synapse needs to create an acceptor. This parameter should contain the URL of the file which contains the FIX configuration for the acceptor. (See sample 257)
If a service needs to send FIX messages to a remote acceptor Synapse should create an initiator. This parameter should contain the URL of the file which contains the FIX configuration for the initiator. (See sample 257)
The type of message store to be used with the acceptor. Allowed values for this parameter are 'file', 'jdbc', 'memory' and 'sleepycat'. If not specified memory based message store will be used by default. Additional parameters required to configure each of the message stores should be specified in the acceptor configuration file.
Same as the above but applies only for the initiators. Additional parameters required to configure each of the message stores should be specified in the initiator configuration file.
Specifies the transport level log factory to be used to log messages going through the acceptor. FIX messages are logged without putting them in SOAP envelopes at this level. Accepted values are 'console', 'file' and 'jdbc'. If not specified no logging will be done at the transport level. Additional parameters required to configure each of the lof factories should be specified in the acceptor configuration file.
Specifies the transport level log factory to be used to log messages going through the initiator. Functionality is similar to the above. Additional parameters required to configure each of the lof factories should be specified in the initiator configuration file.
If a response FIX message sent from Synapse to a remote FIX engine should be forwarded from the remote engine to another party this parameter can be used to set the DeliverToCompID field of the messages at Synapse.
If a response FIX message sent from Synapse to a remote FIX engine should be forwarded from the remote engine to another party this parameter can be used to set the DeliverToSubID field of the messages at Synapse.
If a response FIX message sent from Synapse to a remote FIX engine should be forwarded from the remote engine to another party this parameter can be used to set the DeliverToLocationID field of the messages at Synapse.
Used when messages coming over a different protocol has to be forwarded over FIX. The value must be equal to the name of the service and the scope must be 'axis2-client' (See sample 258)
When there are multiple responses to a FIX request and when we need only one of them to be sent to the original requester this parameter has to be set to 'false'. This mostly comes handy when the original requester is communicating over a different protocol (like HTTP). If this parameter is not set to 'false' at such scenarios messages might get into a loop. (See sample 258)
When the FIX messages sent to Synapse should not be forwarded to a FIX session with a different BeginString value this parameter can be set to 'true'. Setting this parameter to 'true' will enforce this restriction.