Azure Core shared library for Java

Azure Core provides shared primitives, abstractions, and helpers for modern Java Azure SDK client libraries. These libraries follow the Azure SDK Design Guidelines for Java and can be easily identified by package names starting with com.azure and module names starting with azure-, e.g. com.azure.storage.blobs would be found within the /sdk/storage/azure-storage-blob directory. A more complete list of client libraries using Azure Core can be found here.

Azure Core allows client libraries to expose common functionality consistently, so that once you learn how to use these APIs in one client library, you will know how to use them in other client libraries.

Getting started

Prerequisites

A Java Development Kit (JDK), version 8 or later.
- Here are details about Java 8 client compatibility with Azure Certificate Authority.

Include the package

Include the BOM file

Please include the azure-sdk-bom to your project to take dependency on the General Availability (GA) version of the library. In the following snippet, replace the {bom_version_to_target} placeholder with the version number. To learn more about the BOM, see the AZURE SDK BOM README.

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.azure</groupId>
            <artifactId>azure-sdk-bom</artifactId>
            <version>{bom_version_to_target}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

and then include the direct dependency in the dependencies section without the version tag. Typically, you won't need to install or depend on Azure Core, instead it will be transitively downloaded by your build tool when you depend on client libraries using it.

<dependencies>
    <dependency>
        <groupId>com.azure</groupId>
        <artifactId>azure-core</artifactId>
    </dependency>
</dependencies>

Include direct dependency

If you want to take dependency on a particular version of the library that is not present in the BOM, add the direct dependency to your project as follows.

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-core</artifactId>
    <version>1.57.0</version>
</dependency>

Key concepts

The key concepts of Azure Core (and therefore all Azure client libraries using Azure Core) include:

Configuring service clients, e.g. configuring retries, logging, etc. (HttpTrait<T>, ConfigurationTrait<T>, etc.)
Accessing HTTP response details (Response<T>).
Calling long-running operations (PollerFlux<T>).
Paging and asynchronous streams (ContinuablePagedFlux<T>).
Exceptions for reporting errors from service requests consistently.
Abstractions for representing Azure SDK credentials.
Operation timeouts

These will be introduced by way of the examples presented below.

Examples

Accessing HTTP Response Details Using `Response<T>`

Service clients have methods that call Azure services, we refer call these methods service methods.

Service methods can return a shared Azure Core type Response<T>. This type provides access to both the deserialized result of the service call and to the details of the HTTP response returned from the server.

HTTP pipelines with `HttpPipeline`

HttpPipeline is a construct that contains a list of HttpPipelinePolicy which are applied to a request sequentially to prepare it being sent by an HttpClient.

Exception Hierarchy with `AzureException`

AzureException is the root exception in the hierarchy used in Azure Core. Additional exceptions such as HttpRequestException and HttpResponseException are used to reduce the scope of exception reasons.

Pagination with `ContinuablePagedFlux<T>`

ContinuablePageFlux manages sending an initial page request to a service and retrieving additional pages as the consumer requests more data until the consumer finishes processing or all pages have been consumed.

Long Running Operations with `PollerFlux<T>`

PollerFlux manages sending an initial service request and requesting processing updates on a fix interval until polling is cancelled or reaches a terminal state.

Configuring Builders

Builders are used to create service clients and some TokenCredential implementations. They can be configured with a variety of options, including HttpPipeline and HttpClient for HTTP-based clients and more general options such as Configuration andendpoint. To allow for simpler integration into frameworks such as Spring and to allow generic methods to be used for all builders azure-core provides a set of interfaces that can be implemented to provide the necessary functionality.

HttpTrait

HttpTrait<T> contains methods for setting key configurations for HTTP-based clients. This interface will allow you to configure the HttpClient, HttpPipeline, HttpPipelinePolicys, RetryOptions, HttpLogOptions, and ClientOptions (preferably HttpClientOptions as it is more specific for HTTP-based service clients).

For builders that expose HttpTrait<T>, if an HttpPipeline or HttpClient isn't set a default instance will be created based on classpath configurations and the ClientOptions based to the builder. This can cause confusion if you're expecting specific behavior for your client, such as using a proxy that wasn't loaded from the environment. To avoid this, it is recommended to always set the HttpPipeline or HttpClient in all clients if you're building if your configurations aren't based on the environment running the application.

Credential Traits

Azure Core provides different credentials for authenticating with Azure services. Each credential type has a corresponding trait that can be implemented to provide the credential to the client builder. The following table lists the credential traits and the corresponding credential type.

Credential Trait	Credential Type
`AzureKeyCredentialTrait`	`AzureKeyCredential`
`AzureNamedKeyCredentialTrait`	`AzureNamedKeyCredential`
`AzureSasCredentialTrait`	`AzureSasCredential`
`ConnectionStringCredentialTrait`	`String` (there is no formal type for connection strings)
`KeyCredentialTrait`	`KeyCredential`
`TokenCredentialTrait`	`TokenCredential`

ConfigurationTrait

ConfigurationTrait<T> allows for setting Configuration on service clients. Configuration can be used to pass a set of runtime behaviors to the client builder such as how ProxyOptions are loaded from the environment, implicitly passing credentials to some client builders that support it, and more.

EndpointTrait

EndpointTrait<T> allows for setting the service endpoint on service clients.

Operation Timeouts

Azure SDKs provide a few, consistent ways to configure timeouts on API calls. Each timeout effects a different scope of the Azure SDKs and calling application.

HTTP Timeouts

HTTP timeouts are the lowest level of timeout handling the Azure SDKs provide. These timeouts can be configured when building HttpClients or using HttpClientOptions when building service clients without configuring an HttpClient yourself. The following table lists the HTTP timeout, the corresponding HttpClientOptions method that can be used to set it, environment variable to control the default value, the default value if the environment value isn't set, and a brief description of what the timeout effects.

HTTP Timeout	`HttpClientOptions` Method	Environment Variable	Default Value	Description
Connect Timeout	`setConnectTimeout(Duration)`	AZURE_REQUEST_CONNECT_TIMEOUT	10 seconds	The amount of time for a connection to be established before timing out.
Write Timeout	`setWriteTimeout(Duration)`	AZURE_REQUEST_WRITE_TIMEOUT	60 seconds	The amount of time between each request data write to the network before timing out.
Response Timeout	`setResponseTimeout(Duration)`	AZURE_REQUEST_RESPONSE_TIMEOUT	60 seconds	The amount of time between finishing sending the request to receiving the first response bytes before timing out.
Read Timeout	`setReadTimeout(Duration)`	AZURE_REQUEST_READ_TIMEOUT	60 seconds	The amount of time between each response data read from the network before timing out.

Since these timeouts are closest to the network, if they trigger they will be propagated back through the HttpPipeline and generally should be retried by the RetryPolicy.

HttpPipeline Timeouts

HttpPipeline timeouts are the next level of timeout handling the Azure SDKs provide. These timeouts are configured using an HttpPipelinePolicy and configuring a timeout using either Mono.timeout for asynchronous requests or an ExecutorService with a timed get(long, TimeUnit) for synchronous requests.

Depending on the location within the HttpPipeline, these timeouts may be captured by the RetryPolicy and retried. If the timeout policy is PER_RETRY (HttpPipelinePolicy.getPipelinePosition()) the timeout will be captured by the RetryPolicy as it will be positioned after the RetryPolicy, therefore in its capture scope, if it is PER_CALL retrying the request will need to be handled by application logic.

Service Client Timeouts

Service client timeouts are the highest level of timeout handling the Azure SDKs provide. These timeouts are configured by passing Duration timeout into synchronous service methods that support timeouts or by using Mono.timeout or Flux.timeout on asynchronous service methods.

Since these timeouts are on the API call itself they cannot be captured by any retry mechanisms within the Azure SDKs and must be handled by application logic.

Next steps

Get started with Azure libraries that are built using Azure Core.

Troubleshooting

If you encounter any bugs, please file issues via GitHub Issues or checkout StackOverflow for Azure Java SDK.

Enabling Logging

Azure SDKs for Java provide a consistent logging story to help aid in troubleshooting application errors and expedite their resolution. The logs produced will capture the flow of an application before reaching the terminal state to help locate the root issue. View the logging documentation for guidance about enabling logging.

HTTP Request and Response Logging

HTTP request and response logging can be enabled by setting HttpLogDetailLevel in the HttpLogOptions used to create an HTTP-based service client or by setting the environment variable or system property AZURE_HTTP_LOG_DETAIL_LEVEL. The following table displays the valid options for AZURE_HTTP_LOG_DETAIL_LEVEL and the HttpLogDetailLevel it correlates to (valid options are case-insensitive):

`AZURE_HTTP_LOG_DETAIL_LEVEL` value	`HttpLogDetailLevel` enum
`basic`	`HttpLogDetailLevel.BASIC`
`headers`	`HttpLogDetailLevel.HEADERS`
`body`	`HttpLogDetailLevel.BODY`
`body_and_headers`	`HttpLogDetailLevel.BODY_AND_HEADERS`
`bodyandheaders`	`HttpLogDetailLevel.BODY_AND_HEADERS`

All other values, or unsupported values, result in HttpLogDetailLevel.NONE, or disabled HTTP request and response logging. Logging must be enabled to log HTTP requests and responses. Logging of HTTP headers requires verbose logging to be enabled. The following table explains what logging is enabled for each HttpLogDetailLevel:

`HttpLogDetailLevel` value	Logging enabled
`HttpLogDetailLevel.NONE`	No HTTP request or response logging
`HttpLogDetailLevel.BASIC`	HTTP request method, response status code, and request and response URL
`HttpLogDetailLevel.HEADERS`	All of `HttpLogDetailLevel.BASIC` and request and response headers if the log level is `verbose`
`HttpLogDetailLevel.BODY`	All of `HttpLogDetailLevel.BASIC` and request and response body if it's under 10KB in size
`HttpLogDetailLevel.BODY_AND_HEADERS`	All of `HttpLogDetailLevel.HEADERS` and `HttpLogDetailLevel.BODY`

Contributing

For details on contributing to this repository, see the contributing guide.

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request