中间件是一种独立的系统软件或服务程序，分布式应用软件借助这种软件在不同的技术之间共享资源。中间件位于客户机/ 服务器的操作系统之上，管理计算机资源和网络通讯。是连接两个独立应用程序或独立系统的软件。相连接的系统，即使它们具有不同的接口，但通过中间件相互之间仍能交换信息。执行中间件的一个关键途径是信息传递。通过中间件，应用程序可以工作于多平台或 OS 环境。
Definition
Middleware is computer software that connects software components and applications. The software consists of a set of enabling services that allow multiple processes running on one or more machines to interact across a network. This technology evolved to provide for interoperability in support of the move to coherent distributed architectures, which are used most often to support and simplify complex, distributed applications. It includes web servers, transaction monitors, and messaging-and-queueing software.
中间件是一类连接软件组件和应用的计算机软件，它包括一组服务，以便于运行在一台或多台机器上的多个软件通过网络进行交互。该技术所提供的互操作性，推动了一致分布式体系架构
的演进。该架构通常用于支持分布式应用程序并简化其复杂度，它包括web服务器、事务监控器和消息队列软件。
中间件的一些特点
  满足大量应用的需要 ；
  运行于多种硬件和OS平台 ；
  支持分布式计算，提供跨网络、硬件和OS平台的透明性的应用或服务的交互功能 ；
  支持标准的协议 ；
  支持标准的接口。
  中间件可以应用于以下情形，如连接公司 LAN和早期系统、交换两个邮件系统间的信息、支持 web 客户机与数据库服务器交换信息等。
  由于标准接口对于可移植性和标准协议对于互操作性的重要性，中间件已成为许多标准化
工作的主要部分。对于应用软件开发，中间件远比操作系统和网络服务更为重要，中间件提供的程序接口定义了一个相对稳定的高层应用环境，不管底层的计算机硬件和系统软件怎样更新换代，只要将中间件升级更新，并保持中间件对外的接口定义不变，应用软件几乎不需任何修改，从而保护了企业在应用软件开发和维护中的重大投资。
中间件(middleware)是基础软件的一大类，属于可复用软件的范畴。顾名思义，中间件处于操作系统软件与用户的应用软件的中间。
  中间件在操作系统、网络和数据库之上，应用软件的下层，总的作用是为处于自己上层的应用软件提供运行与开发的环境，帮助用户灵活、高效地开发和集成复杂的应用软件。在众多关于中间件的定义中，比较普遍被接受的是IDC表述的：中间件是一种独立的系统软件或服务程序，分布式应用软件借助这种软件在不同的技术之间共享资源，中间件位于客户机服务器的操作系统之上，管理计算资源和网络通信。
  IDC对中间件的定义表明，中间件是一类软件，而非一种软件;中间件不仅仅实现互连，还要实现应用之间的互操作;中间件是基于分布式处理的软件，最突出的特点是其网络通信功能。
The difference between java and c++
Similarities and Differences
This list of similarities and differences is based heavily on The Java Language Environment, A White Paper by James Gosling and Henry McGilton java.sun/doc/language_environment/ and the soon-to-be published book, Thinking in Java by Bruce Eckel, www.EckelObjects/. At least these were the correct URLs at one point in time. Be aware, however, that the web is a dynamic environment and the URLs may change in the future.
Java does not support typedefs, defines, or a preprocessor. Without a preprocessor, there are no provisions【规定】 for including header files.
Since Java does not have a preprocessor there is no concept of #define macros or manifest constants. However, the declaration of named constants is supported in Java through use of the final keyword.
Java does not support enums but, as mentioned above, does support named constants.
Java supports classes, but does not support structures or unions.
All stand-alone C++ programs require a function named main and can have numerous other functions, including both stand-alone functions【独立函数】 and functions, which are members of a class. There are no stand-alone functions in Java. Instead, there are only functions that are members of a class, usually called methods. Global functions and global data are not allowed in Java.
All classes in Java ultimately inherit from the Object class. This is significantly different from C++ where it is possible to create inheritance trees that are completely unrelated to one another.
All function or method definitions in Java are contained within the class definition. To a C++ programmer, they may look like inline function definitions, but they aren't. Java doesn't allow the programmer to request that a function be made inline, at least not directly.
Both C++ and Java support class (static) methods or functions that can be called without the requirement to instantiate an object of the class.
The interface keyword in Java is used to create the equivalence of an abstract base class containing only method declarations and constants. No variable data members or method definitions are allowed. (True abstract base classes can also be created in Java.) The interface concept is not supported by C++.
Java does not support multiple inheritance. To some extent, the interface feature provides the desirable features of multiple inheritance to a Java program without some of the underlying problems.
While Java does not support multiple inheritance, single inheritance in Java is similar to C++, but the manner in which you implement inheritance differs significantly, especially with respect to the use of constructors in the inheritance chain.
In addition to the access specifiers applied to individual members of a class, C++ allows yo
u to provide an additional access specifier when inheriting from a class. This latter concept is not supported by Java.
Java does not support the goto statement (but goto is a reserved word). However, it does support labeled break and continue statements, a feature not supported by C++. In certain restricted situations, labeled break and editordoesnotcontainamaintypecontinue statements can be used where a goto statement might otherwise be used.