It’s a web application
Web applications are applications built on the technology that powers the Web. The HTTP protocol
and the associated programming paradigm are a prominent part of this technology set. In Java, the
raw low-level HTTP and related infrastructure is abstracted out as a higher-level API and managed
components. At the heart of this abstraction is the Servlet specification, which wraps HTTP methods
and HTTP protocol handling in objects. Web applications written in Java are packaged with all assets,
associated libraries, class files, and any other resources into a special archive file format: a web appli-
cation archive (WAR). These WAR files are deployed on a servlet container or an application server
(which contains a servlet container).
Most data services, especially LCDS and BlazeDS, are web applications and exist as WAR files. The
remoting gateway is a servlet, and data service elements are web components. A little later, in the sec-
tion “Downloading and deploying the web application,” you will see how deploying LCDS or BlazeDS
is identical to deploying any other web application distributed in a WAR file format.
In both BlazeDS and LCDS, the primary communication responsibilities are handled by a message bro-
ker, which is created on startup by a servlet called the MessageBrokerServlet. The application server’s
standard class loader loads it like any other servlet. This message broker is extremely flexible, and all
types of available services and endpoints can be configured for it fairly easily. All such configurations
reside in an XML configuration file, which I talk about later in the section “Configuring data services.”
Protocols, channels, destinations, and endpoints
One of the primary advantages of data services is their use of AMF to transmit data between Flex and
Java. AMF is a binary protocol, and the Flash Player natively supports it. Therefore, transmission using
AMF is fast and efficient. AMF is a high-level (application layer) protocol that uses HTTP for commu-
nication. Almost all data services dialog happens over HTTP or its secure alternative, HTTPS. AMF spec-
ification is now available under the open source license and is accessible for download at
http://download.macromedia.com/pub/labs/amf/amf3_spec_121207.pdf. When remoting, AMF is
marshaled and unmarshaled at both ends (Java and Flex) for the data interchange to work.
The data services messaging module and media server use RTMP. LCDS and FMS support RTMP, but
BlazeDS does not. BlazeDS uses HTTP tunneling and AMF long pooling to achieve a push-based model.
Red5 (http://osflash.org/red5), an open source alternative to Flash Media Server, partially reverse-
engineers RTMP and provides streaming capabilities over this derived protocol.
Apart from AMF over HTTP and RTMP, the Flash Player also supports Transmission Control Protocol
(TCP) over Sockets. TCP is a protocol from the Internet protocol suite that facilitates reliable ordered
delivery of byte streams. Secure versions of the protocol, such as AMF and HTTP over Secure Sockets
Layer (SSL) and RTMP over Transport Layer Security (TLS), can be used as well. Both SSL and TLS are
cryptographic protocols that facilitate secure communication over the Internet. TLS is a newer gener-
ation protocol compared to SSL. Although similar, SSL and TLS are not interchangeable. TLS 1.0 is a
standard that emerged after SSL 3.0. These protocols involve endpoint authentication, message
integrity, and key-based encryption. Both protocols support a bunch of cryptographic algorithms
including RSA. RSA is a popular cryptographic algorithm for public key cryptography, which involves
two different keys, one to encrypt a message and another to decrypt it.
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CHAPTER 7
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yinmozhen2012-12-07我以为是安装包呢，下错了~
