API 管理转换策略API Management transformation policies

• 05/09/2020
• • 
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本主题提供以下 API 管理策略的参考。This topic provides a reference for the following API Management policies. 有关添加和配置策略的信息，请参阅 API 管理中的策略。For information on adding and configuring policies, see Policies in API Management.

转换策略Transformation policies

• 将 JSON 转换为 XML - 将请求或响应正文从 JSON 转换为 XML。Convert JSON to XML - Converts request or response body from JSON to XML.

• 将 XML 转换为 JSON - 将请求或响应正文从 XML 转换为 JSON。Convert XML to JSON - Converts request or response body from XML to JSON.

• 查找并替换正文中的字符串 - 查找请求或响应子字符串，并将其替换为不同的子字符串。Find and replace string in body - Finds a request or response substring and replaces it with a different substring.

• 在内容中屏蔽 URL - 重写（屏蔽）响应正文中的链接，使其通过网关指向等效的链接。Mask URLs in content - Re-writes (masks) links in the response body so that they point to the equivalent link via the gateway.

• 设置后端服务 - 更改传入请求的后端服务。Set backend service - Changes the backend service for an incoming request.

• 设置正文 - 设置传入和传出请求的消息正文。Set body - Sets the message body for incoming and outgoing requests.

• 设置 HTTP 标头 - 向现有的响应和/或请求标头赋值，或者添加新的响应和/或请求标头。Set HTTP header - Assigns a value to an existing response and/or request header or adds a new response and/or request header.

• 设置查询字符串参数 - 添加、删除请求查询字符串参数或替换其值。Set query string parameter - Adds, replaces value of, or deletes request query string parameter.

• 重写 URL - 将请求 URL 从其公用格式转换为 Web 服务所需的格式。Rewrite URL - Converts a request URL from its public form to the form expected by the web service.

• 使用 XSLT 转换 XML - 在请求或响应正文中将 XSL 转换应用到 XML。Transform XML using an XSLT - Applies an XSL transformation to XML in the request or response body.

将 JSON 转换为 XML Convert JSON to XML

json-to-xml 策略将请求或响应正文从 JSON 转换为 XML。The json-to-xml policy converts a request or response body from JSON to XML.

策略语句Policy statement

<json-to-xml apply="always | content-type-json" consider-accept-header="true | false" parse-date="true | false"/>

示例Example

<policies>
    <inbound>
        <base />
    </inbound>
    <outbound>
        <base />
        <json-to-xml apply="always" consider-accept-header="false" parse-date="false"/>
    </outbound>
</policies>

元素Elements

属性Attributes

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站、错误时Policy sections: inbound, outbound, on-error

• 策略范围： 所有范围Policy scopes: all scopes

将 XML 转换为 JSONConvert XML to JSON

xml-to-json 策略将请求或响应正文从 XML 转换为 JSON。The xml-to-json policy converts a request or response body from XML to JSON. 此策略可以用来根据仅用 XML 的后端 Web 服务来提升 API。This policy can be used to modernize APIs based on XML-only backend web services.

策略语句Policy statement

<xml-to-json kind="javascript-friendly | direct" apply="always | content-type-xml" consider-accept-header="true | false"/>

示例Example

<policies>
    <inbound>
        <base />
    </inbound>
    <outbound>
        <base />
        <xml-to-json kind="direct" apply="always" consider-accept-header="false" />
    </outbound>
</policies>

元素Elements

属性Attributes

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站、错误时Policy sections: inbound, outbound, on-error

• 策略范围： 所有范围Policy scopes: all scopes

在正文中查找并替换字符串Find and replace string in body

find-and-replace 策略查找请求或响应子字符串并将其替换为不同的子字符串。The find-and-replace policy finds a request or response substring and replaces it with a different substring.

策略语句Policy statement

<find-and-replace from="what to replace" to="replacement" />

示例Example

<find-and-replace from="notebook" to="laptop" />

元素Elements

属性Attributes

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站、后端、错误时Policy sections: inbound, outbound, backend, on-error

• 策略范围： 所有范围Policy scopes: all scopes

在内容中屏蔽 URLMask URLs in content

redirect-content-urls 策略重写（屏蔽）响应正文中的链接，使其通过网关指向等效的链接。The redirect-content-urls policy re-writes (masks) links in the response body so that they point to the equivalent link via the gateway. 在出站节中用于重写响应正文链接，使之指向网关。Use in the outbound section to re-write response body links to make them point to the gateway. 在入站节中使用，以便获得相反的效果。Use in the inbound section for an opposite effect.

策略语句Policy statement

<redirect-content-urls />

示例Example

<redirect-content-urls />

元素Elements

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站Policy sections: inbound, outbound

• 策略范围： 所有范围Policy scopes: all scopes

设置后端服务Set backend service

使用 set-backend-service 策略将传入请求重定向到一个后端，此后端不同于在 API 设置中为该操作指定的后端。Use the set-backend-service policy to redirect an incoming request to a different backend than the one specified in the API settings for that operation. 此策略将传入请求的后端服务基 URL 更改为在策略中指定的基 URL。This policy changes the backend service base URL of the incoming request to the one specified in the policy.

策略语句Policy statement

<set-backend-service base-url="base URL of the backend service" />

或or

<set-backend-service backend-id="identifier of the backend entity specifying base URL of the backend service" />

示例Example

<policies>
    <inbound>
        <choose>
            <when condition="@(context.Request.Url.Query.GetValueOrDefault("version") == "2013-05")">
                <set-backend-service base-url="http://contoso.com/api/8.2/" />
            </when>
            <when condition="@(context.Request.Url.Query.GetValueOrDefault("version") == "2014-03")">
                <set-backend-service base-url="http://contoso.com/api/9.1/" />
            </when>
        </choose>
        <base />
    </inbound>
    <outbound>
        <base />
    </outbound>
</policies>

在此示例中，所设置的后端服务策略根据查询字符串中传递的版本值将请求路由到一个后端服务，该服务不同于在 API 中指定的服务。In this example the set backend service policy routes requests based on the version value passed in the query string to a different backend service than the one specified in the API.

后端服务基 URL 最初派生自 API 设置。Initially the backend service base URL is derived from the API settings. 因此，请求 URL https://contoso.azure-api.net/api/partners/15?version=2013-05&subscription-key=abcdef 变为 http://contoso.com/api/10.4/partners/15?version=2013-05&subscription-key=abcdef，其中 http://contoso.com/api/10.4/ 是在 API 设置中指定的后端服务 URL。So the request URL https://contoso.azure-api.net/api/partners/15?version=2013-05&subscription-key=abcdef becomes http://contoso.com/api/10.4/partners/15?version=2013-05&subscription-key=abcdef where http://contoso.com/api/10.4/ is the backend service URL specified in the API settings.

应用 <choose> 策略语句时，后端服务基 URL 可能会再次更改为 http://contoso.com/api/8.2 或 http://contoso.com/api/9.1，具体取决于版本请求查询参数的值。When the <choose> policy statement is applied the backend service base URL may change again either to http://contoso.com/api/8.2 or http://contoso.com/api/9.1, depending on the value of the version request query parameter. 例如，如果值为 "2013-15"，最终请求 URL 将变为 http://contoso.com/api/8.2/partners/15?version=2013-05&subscription-key=abcdef。For example, if the value is "2013-15" the final request URL becomes http://contoso.com/api/8.2/partners/15?version=2013-05&subscription-key=abcdef.

如果需要进一步转换请求，可使用其他转换策略。If further transformation of the request is desired, other Transformation policies can be used. 例如，在将请求路由到特定于版本的后端以后，要删除版本查询参数，可以使用设置查询字符串参数策略删除现在的冗余版本属性。For example, to remove the version query parameter now that the request is being routed to a version specific backend, the Set query string parameter policy can be used to remove the now redundant version attribute.

示例Example

<policies>
    <inbound>
        <set-backend-service backend-id="my-sf-service" sf-partition-key="@(context.Request.Url.Query.GetValueOrDefault("userId","")" sf-replica-type="primary" />
    </inbound>
    <outbound>
        <base />
    </outbound>
</policies>

在此示例中，策略使用 userId 查询字符串作为分区键并使用该分区的主要副本，将请求路由到 Service Fabric 后端。In this example the policy routes the request to a service fabric backend, using the userId query string as the partition key and using the primary replica of the partition.

元素Elements

属性Attributes

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、后端Policy sections: inbound, backend

• 策略范围： 所有范围Policy scopes: all scopes

设置正文Set body

使用 set-body 策略设置传入和传出请求的消息正文。Use the set-body policy to set the message body for incoming and outgoing requests. 可以使用 context.Request.Body 属性或 context.Response.Body 访问消息正文，具体取决于策略是在入站节中还是在出站节中。To access the message body you can use the context.Request.Body property or the context.Response.Body, depending on whether the policy is in the inbound or outbound section.

有关详细信息，请参阅上下文变量表中的 context.Request.Body、context.Response.Body、IMessage 部分。For more information, see the context.Request.Body, context.Response.Body, and the IMessage sections in the Context variable table.

策略语句Policy statement

<set-body>new body value as text</set-body>

示例Examples

文字文本示例Literal text example

<set-body>Hello world!</set-body>

示例：访问字符串形式的正文。Example accessing the body as a string. 请注意，我们会保留原始请求正文，以便稍后可以在管道中进行访问。Note that we are preserving the original request body so that we can access it later in the pipeline.

<set-body>
@{ 
    string inBody = context.Request.Body.As<string>(preserveContent: true); 
    if (inBody[0] =='c') { 
        inBody[0] = 'm'; 
    } 
    return inBody; 
}
</set-body>

示例：访问 JObject 形式的正文。Example accessing the body as a JObject. 请注意，由于我们不保留原始请求正文，因此稍后在管道进行访问将产生异常。Note that since we are not reserving the original request body, accessing it later in the pipeline will result in an exception.

<set-body> 
@{ 
    JObject inBody = context.Request.Body.As<JObject>(); 
    if (inBody.attribute == <tag>) { 
        inBody[0] = 'm'; 
    } 
    return inBody.ToString(); 
} 
</set-body>

根据产品筛选响应Filter response based on product

以下示例演示了如何进行内容筛选，方法是：在使用 Starter 产品时删除从后端服务接收的响应中的数据元素。This example shows how to perform content filtering by removing data elements from the response received from the backend service when using the Starter product.

<!-- Copy this snippet into the outbound section to remove a number of data elements from the response received from the backend service based on the name of the api product -->
<choose>
  <when condition="@(context.Response.StatusCode == 200 && context.Product.Name.Equals("Starter"))">
    <set-body>@{
        var response = context.Response.Body.As<JObject>();
        foreach (var key in new [] {"minutely", "hourly", "daily", "flags"}) {
          response.Property (key).Remove ();
        }
        return response.ToString();
      }
    </set-body>
  </when>
</choose>

将 Liquid 模板用于设置正文Using Liquid templates with set body

可将 set-body 策略配置为使用 Liquid 模板语言以转换请求或响应正文。The set-body policy can be configured to use the Liquid templating language to transform the body of a request or response. 如需完全重设消息格式，则此模板非常有用。This can be very effective if you need to completely reshape the format of your message.

使用 Liquid 模板将 JSON 转换为 SOAPConvert JSON to SOAP using a Liquid template

<set-body template="liquid">
    <soap:Envelope xmlns="http://tempuri.org/" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
        <soap:Body>
            <GetOpenOrders>
                <cust>{{body.getOpenOrders.cust}}</cust>
            </GetOpenOrders>
        </soap:Body>
    </soap:Envelope>
</set-body>

使用 Liquid 模板转换 JSONTransform JSON using a Liquid template

{
"order": {
    "id": "{{body.customer.purchase.identifier}}",
    "summary": "{{body.customer.purchase.orderShortDesc}}"
    }
}

元素Elements

属性Properties

对于访问请求和响应信息，Liquid 模板可绑定到具有以下属性的上下文对象：For accessing information about the request and response, the Liquid template can bind to a context object with the following properties:

context.
    Request.
        Url
        Method
        OriginalMethod
        OriginalUrl
        IpAddress
        MatchedParameters
        HasBody
        ClientCertificates
        Headers

    Response.
        StatusCode
        Method
        Headers
Url.
    Scheme
    Host
    Port
    Path
    Query
    QueryString
    ToUri
    ToString

OriginalUrl.
    Scheme
    Host
    Port
    Path
    Query
    QueryString
    ToUri
    ToString

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站、后端Policy sections: inbound, outbound, backend

• 策略范围： 所有范围Policy scopes: all scopes

设置 HTTP 标头Set HTTP header

set-header 策略向现有的响应和/或请求标头赋值，或者添加新的响应和/或请求标头。The set-header policy assigns a value to an existing response and/or request header or adds a new response and/or request header.

在 HTTP 消息中插入 HTTP 标头列表。Inserts a list of HTTP headers into an HTTP message. 将此策略放到入站管道中后，它将为传递给目标服务的请求设置 HTTP 标头。When placed in an inbound pipeline, this policy sets the HTTP headers for the request being passed to the target service. 将此策略放到出站管道中后，它将为发送到网关客户端的响应设置 HTTP 标头。When placed in an outbound pipeline, this policy sets the HTTP headers for the response being sent to the gateway’s client.

策略语句Policy statement

<set-header name="header name" exists-action="override | skip | append | delete">
    <value>value</value> <!--for multiple headers with the same name add additional value elements-->
</set-header>

示例Examples

示例 - 添加标头，替代现有标头Example - adding header, override existing

<set-header name="some header name" exists-action="override">
    <value>20</value>
</set-header>

示例 - 删除标头Example - removing header

 <set-header name="some header name" exists-action="delete" />

将上下文信息转发到后端服务Forward context information to the backend service

此示例演示了如何在 API 级别应用策略，以便将上下文信息提供给后端服务。This example shows how to apply policy at the API level to supply context information to the backend service.

<!-- Copy this snippet into the inbound element to forward some context information, user id and the region the gateway is hosted in, to the backend service for logging or evaluation -->
<set-header name="x-request-context-data" exists-action="override">
  <value>@(context.User.Id)</value>
  <value>@(context.Deployment.Region)</value>
</set-header>

有关详细信息，请参阅策略表达式和上下文变量。For more information, see Policy expressions and Context variable.

元素Elements

属性Properties

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站、后端、错误时Policy sections: inbound, outbound, backend, on-error

• 策略范围： 所有范围Policy scopes: all scopes

设置查询字符串参数Set query string parameter

set-query-parameter 策略添加、删除请求查询字符串参数或替换其值。The set-query-parameter policy adds, replaces value of, or deletes request query string parameter. 可用于传递后端服务所需的查询参数，这些参数是可选的或者永远不能出现在请求中。Can be used to pass query parameters expected by the backend service which are optional or never present in the request.

策略语句Policy statement

<set-query-parameter name="param name" exists-action="override | skip | append | delete">
    <value>value</value> <!--for multiple parameters with the same name add additional value elements-->
</set-query-parameter>

示例Example

<set-query-parameter name="api-key" exists-action="skip">
  <value>12345678901</value>
</set-query-parameter>

将上下文信息转发到后端服务Forward context information to the backend service

此示例演示了如何在 API 级别应用策略，以便将上下文信息提供给后端服务。This example shows how to apply policy at the API level to supply context information to the backend service.

<!-- Copy this snippet into the inbound element to forward a piece of context, product name in this example, to the backend service for logging or evaluation -->
<set-query-parameter name="x-product-name" exists-action="override">
  <value>@(context.Product.Name)</value>
</set-query-parameter>

有关详细信息，请参阅策略表达式和上下文变量。For more information, see Policy expressions and Context variable.

元素Elements

属性Properties

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、后端Policy sections: inbound, backend

• 策略范围： 所有范围Policy scopes: all scopes

重写 URLRewrite URL

rewrite-uri 策略将请求 URL 从其公用格式转换为 Web 服务所需的格式，如以下示例所示。The rewrite-uri policy converts a request URL from its public form to the form expected by the web service, as shown in the following example.

• 公共 URL - http://api.example.com/storenumber/ordernumberPublic URL - http://api.example.com/storenumber/ordernumber

• 请求 URL - http://api.example.com/v2/US/hardware/storenumber&ordernumber?City&StateRequest URL - http://api.example.com/v2/US/hardware/storenumber&ordernumber?City&State

  如果要将用户和/或浏览器友好的 URL 转换成 Web 服务所需的 URL 格式，则可使用此策略。This policy can be used when a human and/or browser-friendly URL should be transformed into the URL format expected by the web service. 应用此策略的前提是公开备用的 URL 格式，例如简洁 URL、RESTful URL、用户友好的 URL 或 SEO 友好的 URL。这些 URL 是纯结构化 URL，不包含查询字符串，只包含资源的路径（在方案和颁发机构的后面）。This policy only needs to be applied when exposing an alternative URL format, such as clean URLs, RESTful URLs, user-friendly URLs or SEO-friendly URLs that are purely structural URLs that do not contain a query string and instead contain only the path of the resource (after the scheme and the authority). 通常会出于美观、可用性或搜索引擎优化 (SEO) 目的使用这种 URL。This is often done for aesthetic, usability, or search engine optimization (SEO) purposes.

策略语句Policy statement

<rewrite-uri template="uri template" copy-unmatched-params="true | false" />

示例Example

<policies>
    <inbound>
        <base />
        <rewrite-uri template="/v2/US/hardware/{storenumber}&{ordernumber}?City=city&State=state" />
    </inbound>
    <outbound>
        <base />
    </outbound>
</policies>

<!-- Assuming incoming request is /get?a=b&c=d and operation template is set to /get?a={b} -->
<policies>
    <inbound>
        <base />
        <rewrite-uri template="/put" />
    </inbound>
    <outbound>
        <base />
    </outbound>
</policies>
<!-- Resulting URL will be /put?c=d -->

<!-- Assuming incoming request is /get?a=b&c=d and operation template is set to /get?a={b} -->
<policies>
    <inbound>
        <base />
        <rewrite-uri template="/put" copy-unmatched-params="false" />
    </inbound>
    <outbound>
        <base />
    </outbound>
</policies>
<!-- Resulting URL will be /put -->

元素Elements

属性Attributes

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站Policy sections: inbound

• 策略范围： 所有范围Policy scopes: all scopes

使用 XSLT 转换 XMLTransform XML using an XSLT

Transform XML using an XSLT 策略在请求或响应正文中将 XSL 转换应用到 XML。The Transform XML using an XSLT policy applies an XSL transformation to XML in the request or response body.

策略语句Policy statement

<xsl-transform>
    <parameter name="User-Agent">@(context.Request.Headers.GetValueOrDefault("User-Agent","non-specified"))</parameter>
    <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
        <xsl:output method="xml" indent="yes" />
        <xsl:param name="User-Agent" />
        <xsl:template match="* | @* | node()">
            <xsl:copy>
                <xsl:if test="self::* and not(parent::*)">
                    <xsl:attribute name="User-Agent">
                        <xsl:value-of select="$User-Agent" />
                    </xsl:attribute>
                </xsl:if>
                <xsl:apply-templates select="* | @* | node()" />
            </xsl:copy>
        </xsl:template>
    </xsl:stylesheet>
  </xsl-transform>

示例Example

<policies>
  <inbound>
      <base />
  </inbound>
  <outbound>
      <base />
      <xsl-transform>
        <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
            <xsl:output omit-xml-declaration="yes" method="xml" indent="yes" />
            <!-- Copy all nodes directly-->
            <xsl:template match="node()| @*|*">
                <xsl:copy>
                    <xsl:apply-templates select="@* | node()|*" />
                </xsl:copy>
            </xsl:template>
        </xsl:stylesheet>
    </xsl-transform>
  </outbound>
</policies>

元素Elements

使用情况Usage

此策略可在以下策略节和范围中使用。This policy can be used in the following policy sections and scopes.

• 策略节： 入站、出站Policy sections: inbound, outbound

• 策略范围： 所有范围Policy scopes: all scopes

后续步骤Next steps

有关详细信息，请参阅以下主题：For more information, see the following topics:

• API 管理中的策略Policies in API Management
• 策略参考，获取策略语句及其设置的完整列表Policy Reference for a full list of policy statements and their settings
• 策略示例Policy samples