Spring Web服务详解：合同优先的实现

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"Spring Web Services 参考指南涵盖了关于 Spring Web Services 的所有内容，特别是 WS 安全性方面的知识。本书旨在提供一个合同优先（Contract-First）的 Web 服务开发方法，强调了使用 Spring 框架创建稳定、可重用且易于维护的 Web 服务的实践和理念。" 在 Spring Web Services 中，主要讨论以下几个核心知识点： 1. **什么是 Spring Web Services**： - Spring Web Services 是一个框架，用于创建基于 SOAP 的、面向契约的 Web 服务。它支持合同优先的方法，这意味着开发者首先定义服务的接口（通常是 WSDL 文件），然后实现该接口。 - Spring Web Services 强调了 XML 消息交换，并提供了创建和消费这些消息的工具。 2. **合同优先（Contract-First）的开发方式**： - 合同优先强调先定义服务的行为和数据格式（WSDL 和 XSD），然后再编写实现代码。这种方式有助于减少因设计不当导致的错误，提高了代码的稳定性。 - 文档中提到了对象与 XML 的不匹配问题，如 XSD 扩展、不可移植类型以及循环引用图，这些都是合同优先方法试图解决的问题。 3. **为什么选择合同优先？** - **稳定性**：合同优先可以避免因编码错误导致的服务变更，降低了服务的脆弱性。 - **性能**：由于定义明确的合同，可以进行高效的编译时检查，从而提高性能。 - **重用性**：清晰的接口易于其他系统理解和集成，增加了组件的重用可能性。 - **版本控制**：有了明确的合同，可以更好地管理服务升级和向后兼容性。 4. **编写合同优先的 Web 服务**： - 这一部分详细介绍了如何创建一个简单的 Web 服务，包括定义消息（如 Holiday、Employee 和 HolidayRequest）、数据合同、服务合同，以及如何创建项目、实现 Endpoint、处理 XML 消息和路由到 Endpoint。 - 在实践中，开发者会使用 Spring 提供的工具生成服务的 WSDL 文件，并实现相应的消息处理器。 5. **共享组件**： - 在参考部分，还涵盖了 Spring Web Services 中的共享组件，这些组件可能包括消息处理、安全、事务管理和与其他 Spring 模块的集成等。此外，书中还可能深入探讨了 WS-Security，这是 Web 服务中的一个重要方面，涉及到消息的安全传输、身份验证和授权等关键问题。Spring 提供了对 WS-Security 标准的支持，帮助开发者在 Web 服务中实施安全性。 "Spring Web Services reference" 是一本详尽的指南，适合想要深入了解如何使用 Spring 框架创建安全、稳定的合同优先 Web 服务的开发者。通过遵循书中提供的步骤和最佳实践，开发者能够有效地构建和管理符合企业级标准的 Web 服务。

Chapter 3. Writing Contract-First Web Services

3.1. Introduction

This tutorial shows you how to write contract-first Web services, that is, developing web services that start with

the XML Schema/WSDL contract first followed by the Java code second. Spring-WS focuses on this

development style, and this tutorial will help you get started. Note that the first part of this tutorial contains

almost no Spring-WS specific information: it is mostly about XML, XSD, and WSDL. The second part

focusses on implementing this contract using Spring-WS .

The most important thing when doing contract-first Web service development is to try and think in terms of

XML. This means that Java-language concepts are of lesser importance. It is the XML that is sent across the

wire, and you should focus on that. The fact that Java is used to implement the Web service is an

implementation detail. An important detail, but a detail nonetheless.

In this tutorial, we will define a Web service that is created by a Human Resources department. Clients can

send holiday request forms to this service to book a holiday.

3.2. Messages

In this section, we will focus on the actual XML messages that are sent to and from the Web service. We will

start out by determining what these messages look like.

3.2.1. Holiday

In the scenario, we have to deal with holiday requests, so it makes sense to determine what a holiday looks like

in XML:

</Holiday>

A holiday consists of a start date and an end date. We have also decided to use the standard ISO 8601 date

format for the dates, because that will save a lot of parsing hassle. We have also added a namespace to the

element, to make sure our elements can used within other XML documents.

3.2.2. Employee

There is also the notion of an employee in the scenario. Here is what it looks like in XML:

<FirstName>Arjen</FirstName>

<LastName>Poutsma</LastName>

</Employee>

We have used the same namespace as before. If this <Employee/> element could be used in other scenarios, it

might make sense to use a different namespace, such as http://mycompany.com/employees/schemas.

Spring-WS (1.5.0-m2) 8

3.2.3. HolidayRequest

Both the holiday and employee element can be put in a <HolidayRequest/>:

</Holiday>

<FirstName>Arjen</FirstName>

<LastName>Poutsma</LastName>

</Employee>

</HolidayRequest>

The order of the two elements does not matter: <Employee/> could have been the first element just as well.

What is important is that all of the data is there. In fact, the data is the only thing that is important: we are

taking a data-driven approach.

3.3. Data Contract

Now that we have seen some examples of the XML data that we will use, it makes sense to formalize this into a

schema. This data contract defines the message format we accept. There are four different ways of defining

such a contract for XML:

• DTDs

• XML Schema (XSD)

• RELAX NG

• Schematron

DTDs have limited namespace support, so they are not suitable for Web services. Relax NG and Schematron

certainly are easier than XML Schema. Unfortunately, they are not so widely supported across platforms. We

will use XML Schema.

By far the easiest way to create an XSD is to infer it from sample documents. Any good XML editor or Java

IDE offers this functionality. Basically, these tools use some sample XML documents, and generate a schema

from it that validates them all. The end result certainly needs to be polished up, but it's a great starting point.

Using the sample described above, we end up with the following generated schema:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

elementFormDefault="qualified"

targetNamespace="http://mycompany.com/hr/schemas"

xmlns:hr="http://mycompany.com/hr/schemas">

<xs:element name="HolidayRequest">

<xs:complexType>

<xs:sequence>

<xs:element ref="hr:Holiday"/>

<xs:element ref="hr:Employee"/>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="Holiday">

<xs:complexType>

<xs:sequence>

<xs:element ref="hr:StartDate"/>

Writing Contract-First Web Services

Spring-WS (1.5.0-m2) 9

<xs:element ref="hr:EndDate"/>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="StartDate" type="xs:NMTOKEN"/>

<xs:element name="EndDate" type="xs:NMTOKEN"/>

<xs:element name="Employee">

<xs:complexType>

<xs:sequence>

<xs:element ref="hr:Number"/>

<xs:element ref="hr:FirstName"/>

<xs:element ref="hr:LastName"/>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:element name="Number" type="xs:integer"/>

<xs:element name="FirstName" type="xs:NCName"/>

<xs:element name="LastName" type="xs:NCName"/>

</xs:schema>

This generated schema obviously can be improved. The first thing to notice is that every type has a root-level

element declaration. This means that the Web service should be able to accept all of these elements as data.

This is not desirable: we only want to accept a <HolidayRequest/>. By removing the wrapping element tags

(thus keeping the types), and inlining the results, we can accomplish this.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

xmlns:hr="http://mycompany.com/hr/schemas"

elementFormDefault="qualified"

targetNamespace="http://mycompany.com/hr/schemas">

<xs:element name="HolidayRequest">

<xs:complexType>

<xs:sequence>

<xs:element name="Holiday" type="hr:HolidayType"/>

<xs:element name="Employee" type="hr:EmployeeType"/>

</xs:sequence>

</xs:complexType>

</xs:element>

<xs:complexType name="HolidayType">

<xs:sequence>

<xs:element name="StartDate" type="xs:NMTOKEN"/>

<xs:element name="EndDate" type="xs:NMTOKEN"/>

</xs:sequence>

</xs:complexType>

<xs:complexType name="EmployeeType">

<xs:sequence>

<xs:element name="Number" type="xs:integer"/>

<xs:element name="FirstName" type="xs:NCName"/>

<xs:element name="LastName" type="xs:NCName"/>

</xs:sequence>

</xs:complexType>

</xs:schema>

The schema still has one problem: with a schema like this, you can expect the following messages to validate:

<EndDate>neither is this</EndDate>

</Holiday>

</HolidayRequest>

Clearly, we must make sure that the start and end date are really dates. XML Schema has an excellent built-in

date type which we can use. We also change the NCNames to strings. Finally, we change the sequence in

<HolidayRequest/> to all. This tells the XML parser that the order of <Holiday/> and <Employee/> is not

significant. Our final XSD now looks like this:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

Writing Contract-First Web Services

Spring-WS (1.5.0-m2) 10

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