Spring Web Services Contract-First教程

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"Spring Web Services 手册是官方提供的参考文档，主要介绍如何使用Spring框架构建合同优先（Contract-First）的Web服务。手册由Arjen Poutsma、Rick Evans和Tareq Abed Rabbo等人编写，版权始于2005年。本手册允许自由复制和分发，但不得收取费用，并需保留版权通知。" Spring Web Services是一个用于构建SOAP Web服务的框架，其设计目标是鼓励采用合同优先的开发方法。在合同优先的模式下，开发者首先定义Web服务的接口，即WSDL（Web服务描述语言），然后基于这个接口实现服务。 1.1. 引言 Spring Web Services旨在帮助开发者创建强类型、与协议无关的Web服务。它支持通过XSD（XML Schema Definition）来定义服务合同，从而确保数据的准确性和互操作性。 1.2. 运行环境手册介绍了运行Spring Web Services所需的基本环境，包括Spring框架的版本要求、Java版本以及其他依赖库。 2.1. 为什么选择合同优先？合同优先的方法强调先定义服务的行为，再进行实现。这种方式有助于减少对象/XML之间的不匹配问题，提高代码的稳定性和可维护性。 2.2. 对象/XML不匹配 2.2.1. XSD扩展 XSD允许定义扩展，以确保数据模型的精确性，这在合同优先的方法中特别有用。 2.2.2. 不便移植的类型某些Java类型可能不适用于跨平台的XML交换，合同优先可以避免这类问题。 2.2.3. 循环引用处理循环数据结构时，合同优先可以提供更清晰的服务边界和更简单的序列化/反序列化逻辑。 2.3. 合同优先与合同最后的对比 2.3.1. 脆弱性合同最后的开发方式可能导致脆弱的API，因为实现可能会先于合同完成，导致后期修改困难。 2.3.2. 性能合同优先可能导致前期工作更多，但长远来看，它有助于优化性能，因为有明确的合同约束。 2.3.3. 可复用性合同优先的服务更易于在多个项目间重用，因为接口清晰且独立于具体实现。 2.3.4. 版本控制随着服务的发展，合同优先使得版本控制更加简单，因为可以独立更新合同而不会影响消费者。 3.1. 编写合同优先的Web服务手册详细讲解了从创建服务合同到实现服务的过程。 3.2. 消息通过实例，如`Holiday`、`Employee`和`HolidayRequest`，解释了如何定义服务的消息结构。 3.3. 数据合同数据合同是服务的核心部分，通过XSD来定义消息的数据结构。 3.4. 服务合同服务合同定义了服务的接口，包括输入和输出的消息，以及服务的业务逻辑。 3.5. 创建项目这部分指导读者如何设置项目结构，准备开发Web服务。 3.6. 实现Endpoint 3.6.1. 处理XML消息解释了如何解析和处理来自客户端的XML消息。 3.6.2. 路由消息到Endpoint 介绍了如何将接收到的消息路由到适当的处理逻辑。 3.7. 发布WSDL 最后，手册描述了如何公开WSDL文件，使其他系统能够发现和使用Web服务。 "Spring Web Services 手册"提供了详尽的指导，涵盖了从设计服务合同到发布服务的每个步骤，对于想要使用Spring构建Web服务的开发者来说，是一份不可或缺的参考资料。

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 (1.5.4) 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 (1.5.4) 10

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

elementFormDefault="qualified"

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

<xs:element name="HolidayRequest">

<xs:complexType>

<xs:all>

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

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

</xs:all>

</xs:complexType>

</xs:element>

<xs:complexType name="HolidayType">

<xs:sequence>

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

<xs:element name="EndDate" type="xs:date"/> ❷

</xs:sequence> ❷

</xs:complexType>

<xs:complexType name="EmployeeType">

<xs:sequence>

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

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

<xs:element name="LastName" type="xs:string"/> ❸

</xs:sequence> ❸

</xs:complexType>

</xs:schema>

❶ all tells the XML parser that the order of <Holiday/> and <Employee/> is not significant.

❷ We use the xsd:date data type, which consist of a year, month, and day, for <StartDate/> and

<EndDate/>.

❸ xsd:string is used for the first and last name.

We store this file as hr.xsd.

3.4. Service contract

A service contract is generally expressed as a WSDL file. Note that in Spring-WS, writing the WSDL by hand

is not required. Based on the XSD and some conventions, Spring-WS can create the WSDL for you, as

explained in the section entitled Section 3.6, “Implementing the Endpoint”. You can skip to the next section if

you want to; the remainder of this section will show you how to write your own WSDL by hand.

We start our WSDL with the standard preamble, and by importing our existing XSD. To separate the schema

from the definition, we will use a separate namespace for the WSDL definitions:

http://mycompany.com/hr/definitions.

<wsdl:definitions xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"

xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"

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

xmlns:tns="http://mycompany.com/hr/definitions"

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

<wsdl:types>

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

<xsd:import namespace="http://mycompany.com/hr/schemas" schemaLocation="hr.xsd"/>

</xsd:schema>

</wsdl:types>

Next, we add our messages based on the written schema types. We only have one message: one with the

<HolidayRequest/> we put in the schema:

<wsdl:message name="HolidayRequest">

<wsdl:part element="schema:HolidayRequest" name="HolidayRequest"/>

</wsdl:message>

Writing Contract-First Web Services

Spring-WS (1.5.4) 11

We add the message to a port type as an operation:

<wsdl:portType name="HumanResource">

<wsdl:operation name="Holiday">

<wsdl:input message="tns:HolidayRequest" name="HolidayRequest"/>

</wsdl:operation>

</wsdl:portType>

That finished the abstract part of the WSDL (the interface, as it were), and leaves the concrete part. The

concrete part consists of a binding, which tells the client how to invoke the operations you've just defined; and

a service, which tells it where to invoke it.

Adding a concrete part is pretty standard: just refer to the abstract part you defined previously, make sure you

use document/literal for the soap:binding elements (rpc/encoded is deprecated), pick a soapAction for the

operation (in this case http://mycompany.com/RequestHoliday, but any URI will do), and determine the

location URL where you want request to come in (in this case http://mycompany.com/humanresources):

<wsdl:definitions xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/"

xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"

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

xmlns:tns="http://mycompany.com/hr/definitions"

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

<wsdl:types>

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

<xsd:import namespace="http://mycompany.com/hr/schemas" ❶

schemaLocation="hr.xsd"/>

</xsd:schema>

</wsdl:types>

<wsdl:message name="HolidayRequest"> ❷

<wsdl:part element="schema:HolidayRequest" name="HolidayRequest"/> ❸

</wsdl:message>

<wsdl:portType name="HumanResource"> ❹

<wsdl:operation name="Holiday">

<wsdl:input message="tns:HolidayRequest" name="HolidayRequest"/> ❷

</wsdl:operation>

</wsdl:portType>

<wsdl:binding name="HumanResourceBinding" type="tns:HumanResource"> ❹❺

<soap:binding style="document" ❻

transport="http://schemas.xmlsoap.org/soap/http"/> ❼

<wsdl:operation name="Holiday">

<soap:operation soapAction="http://mycompany.com/RequestHoliday"/> ❽

<wsdl:input name="HolidayRequest">

<soap:body use="literal"/> ❻

</wsdl:input>

</wsdl:operation>

</wsdl:binding>

<wsdl:service name="HumanResourceService">

<wsdl:port binding="tns:HumanResourceBinding" name="HumanResourcePort"> ❺

<soap:address location="http://localhost:8080/holidayService/"/> ❾

</wsdl:port>

</wsdl:service>

</wsdl:definitions>

❶ We import the schema defined in Section 3.3, “Data Contract”.

❷ We define the HolidayRequest message, which gets used in the portType.

❸ The HolidayRequest type is defined in the schema.

❹ We define the HumanResource port type, which gets used in the binding.

❺ We define the HumanResourceBinding binding, which gets used in the port.

❻ We use a document/literal style.

❼ The literal http://schemas.xmlsoap.org/soap/http signifies a HTTP transport.

❽ The soapAction attribute signifies the SOAPAction HTTP header that will be sent with every request.

❾ The http://localhost:8080/holidayService/ address is the URL where the Web service can be

invoked.

Writing Contract-First Web Services

Spring-WS (1.5.4) 12

This is the final WSDL. We will describe how to implement the resulting schema and WSDL in the next

section.

3.5. Creating the project

In this section, we will be using Maven2 to create the initial project structure for us. Doing so is not required,

but greatly reduces the amount of code we have to write to setup our HolidayService.

The following command creates a Maven2 web application project for us, using the Spring-WS archetype (that

is, project template)

mvn archetype:create -DarchetypeGroupId=org.springframework.ws \

-DarchetypeArtifactId=spring-ws-archetype \

-DarchetypeVersion=1.5.4 \

-DgroupId=com.mycompany.hr \

-DartifactId=holidayService

This command will create a new directory called holidayService. In this directory, there is a

'src/main/webapp' directory, which will contain the root of the WAR file. You will find the standard web

application deployment descriptor 'WEB-INF/web.xml' here, which defines a Spring-WS

MessageDispatcherServlet and maps all incoming requests to this servlet:

<web-app xmlns="http://java.sun.com/xml/ns/j2ee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee

http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"

version="2.4">

<display-name>MyCompany HR Holiday Service</display-name>

<servlet-name>spring-ws</servlet-name>

<servlet-class>org.springframework.ws.transport.http.MessageDispatcherServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>spring-ws</servlet-name>

<url-pattern>/*</url-pattern>

</servlet-mapping>

</web-app>

In addition to the above 'WEB-INF/web.xml' file, you will also need another, Spring-WS-specific configuration

file, named 'WEB-INF/spring-ws-servlet.xml'. This file contains all of the Spring-WS-specific beans such as

EndPoints, WebServiceMessageReceivers, and suchlike, and is used to create a new Spring container. The

name of this file is derived from the name of the attendant servlet (in this case 'spring-ws') with

'-servlet.xml' appended to it. So if you defined a MessageDispatcherServlet with the name 'dynamite',

the name of the Spring-WS-specific configuration file would be 'WEB-INF/dynamite-servlet.xml'.

(You can see the contents of the 'WEB-INF/spring-ws-servlet.xml' file for this example in ???.)

3.6. Implementing the Endpoint

In Spring-WS, you will implement Endpoints to handle incoming XML messages. There are two flavors of

endpoints: message endpoints and payload endpoints. Message endpoints give access to the entire XML

message, including SOAP headers. Typically, the endpoint will only be interested in the payload of the

Writing Contract-First Web Services

Spring-WS (1.5.4) 13

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