xAPI Java

xAPI Java helps you to create applications that send or receive xAPI Statements or Documents.

There are two projects in this Monorepo, xAPI Client and xAPI Model.

Both the xAPI Client and xAPI Model use a fluent interface. Objects are immutable.

CheckStyle is used to enforce the Google Java Style Guide. Sonar performs automatic pull request reviews. CodeQL scans for vulnerabilities. The number of bugs, code smells and vulnerabilities in the codebase can be viewed in SonarCloud. The code coverage and code duplication percentages can also be viewed in SonarCloud. Over three-hundred unit tests ensure conformance with the xAPI specification.

Requirements

xAPI Java requires Java 17 or newer.

xAPI Java Client

The xAPI Java Client can be used by learning record providers (LRP) to communicate with learning record stores (LRS) or a system which follows the LRS requirements of one or more of the xAPI resources.

Getting started

To use the xAPI Java Client include the appropriate XML in the dependencies section of your pom.xml, as shown in the following example:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>getting-started</artifactId>
    <!-- ... -->
    <dependencies>
        <!-- ... -->
        <dependency>
            <groupId>dev.learning.xapi</groupId>
            <artifactId>xapi-client</artifactId>
            <version>1.1.11</version>
        </dependency>
    </dependencies>
</project>

xAPI Java Client is available in the Maven Central Repository.

Configuration

The xAPI Java Client has a Spring AutoConfiguration bean which picks up the following properties:

Property	Description
xapi.client.baseUrl	The base url of the LRS endpoint
xapi.client.username	Username for basic authorization header
xapi.client.password	Password for basic authorization header
xapi.client.authorization	Authorization header (has precedence over the username and password properties)

Properties can be set using any external configuration method supported by Spring Boot.

If you need more specific customization (eg. your LRS needs specific headers, or you want to set the authorization header dynamically) you can create a custom configurer by implementing the XapiClientConfigurer interface.

Advanced Configuration

The xAPI Java Client uses the Spring WebClient. Spring WebClient has default memory limit of 256KB for buffering data. If this limit is exceeded then a DataBufferLimitException will be thrown.

The default memory limit of 256KB for buffering data could be exceeded if the LRS returns a large number of Statements or if the Statements contain attachments.

It is possible to set the memory limit for buffering data with the spring.codec.max-in-memory-size property.

Example:

spring.codec.max-in-memory-size=1MB

Statement Resource

The xAPI Java Client allows applications to store and fetch xAPI Statements.

Getting a Statement

Example:

var response = client.getStatement(r -> r.id("4df42866-40e7-45b6-bf7c-8d5fccbdccd6")).block();

Statement statement = response.getBody();

Getting a Statement with attachments

Example:

var response = client.getStatement(r -> r.id("4df42866-40e7-45b6-bf7c-8d5fccbdccd6").attachments(true).block();

Statement statement = response.getBody();

Getting Statements

Example:

var response = client.getStatements().block();

StatementResult statementResult = response.getBody();

Statement[] statements = statementResult.getStatements();

Getting the next page of Statements

Example:

var response = client.getStatements().block();

var moreResponse = client.getMoreStatements(r -> r.more(response.getBody().getMore())).block();

StatementResult moreStatementResult = moreResponse.getBody();

Statement[] statements = moreStatementResult.getStatements();

Getting Statements as Iterator (and processing them as a Stream)

In most cases it is preferable to use getStatementIterator() instead of getStatments() and getMoreStatements().

Example:

var statements = client.getStatementIterator().block();

// process the first 100 Statements
statements.toStream().limit(100).forEach(s -> {
    // add logic here...
  });

Posting a Statement

Example:

client.postStatement(
    r -> r.statement(s -> s.agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]"))

        .verb(Verb.ATTEMPTED)

        .activityObject(o -> o.id("https://example.com/activity/simplestatement")
            .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))))
    .block();

Posting a Statement with an attachment

Example:

client.postStatement(
    r -> r.statement(s -> s.agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]"))

        .verb(Verb.ATTEMPTED)

        .activityObject(o -> o.id("https://example.com/activity/simplestatement")
            .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))

        .addAttachment(a -> a.content("Simple attachment").length(17).contentType("text/plain")
            .usageType(URI.create("https://example.com/attachments/simplestatement"))
            .addDisplay(Locale.ENGLISH, "text attachment"))

    )).block();

Posting a Signed Statement

Example:

client.postStatement(
    r -> r.signedStatement(s -> s.agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]"))

        .verb(Verb.ATTEMPTED)

        .activityObject(o -> o.id("https://example.com/activity/simplestatement")
            .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement"))),

        keyPair.getPrivate()))
    .block();

Posting Statements

Example:

Statement attemptedStatement = Statement.builder()
    .agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]")).verb(Verb.ATTEMPTED)
    .activityObject(o -> o.id("https://example.com/activity/simplestatement")
        .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))
    .build();

Statement passedStatement = attemptedStatement.toBuilder().verb(Verb.PASSED).build();

client.postStatements(r -> r.statements(attemptedStatement, passedStatement)).block();

Getting a voided Statement

Example:

var response = client.getVoidedStatement(r -> r.id("4df42866-40e7-45b6-bf7c-8d5fccbdccd6")).block();

Statement voidedStatement = response.getBody();

State Resource

The xAPI Java Client allows applications to store, change, fetch, or delete state documents.

Getting a state

Example:

var response = client.getState(r -> r.activityId("https://example.com/activity/1")

    .agent(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .registration("67828e3a-d116-4e18-8af3-2d2c59e27be6")

    .stateId("bookmark"), String.class)

    .block();

String state = response.getBody();

Posting a state

Example:

client.postState(r -> r.activityId("https://example.com/activity/1")

    .agent(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .registration("67828e3a-d116-4e18-8af3-2d2c59e27be6")

    .stateId("bookmark")

    .state("Hello World!"))

    .block();

Putting a state

Example:

client.putState(r -> r.activityId("https://example.com/activity/1")

    .agent(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .registration("67828e3a-d116-4e18-8af3-2d2c59e27be6")

    .stateId("bookmark")

    .state("Hello World!"))

    .block();

Deleting a state

Example:

client.deleteState(r -> r.activityId("https://example.com/activity/1")

    .agent(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .registration("67828e3a-d116-4e18-8af3-2d2c59e27be6")

    .stateId("bookmark"))

    .block();

Samples

The samples folder in this repository contains sample applications that use the xAPI client.

xAPI Model Spring Boot Starter

The xAPI specification has strict rules for API requests/responses formatting. The xAPI Model has inbuilt validation for all of these rules. However, if you plan to use the xAPI Model, you should keep in mind that some activity providers do not fully conform to these rules.

In some cases it may be desirable to turn off some or all of the rules in order to be compatible with a wider range of xAPI activity providers. However, it should be noted that doing this is in violation of the xAPI specification.

The xAPI Model Spring Boot Starter package provides an easy way to turn on/off these validation rules.

Getting started

To use the xAPI Model Spring Boot Starter include the appropriate XML in the dependencies section of your pom.xml, as shown in the following example:

<dependency>
  <groupId>dev.learning.xapi</groupId>
  <artifactId>xapi-model-spring-boot-starter</artifactId>
  <version>1.1.11</version>
</dependency>

xAPI Model Spring Boot Starter is available in the Maven Central Repository.

Configuration

The xAPI Model Spring Boot Starter has a Spring AutoConfiguration bean which picks up the following properties:

Property	Description
xapi.model.validateJson	Fail on trailing JSON tokens
xapi.model.validateProperties	Fail on unknown JSON properties
xapi.model.validateNullValues	Fail on null JSON properties
xapi.model.validateLiterals	Fail on number and boolean JSON properties defined as string
xapi.model.validateObjectType	Fail on invalid JSON objectType property
xapi.model.validateLocale	Fail on invalid Locale strings
xapi.model.validateTimestamp	Fail on negative zero timezone offsets
xapi.model.validateActivityDefinition	Fail on invalid xAPI ActivityDefinition (missing properties)
xapi.model.validateActor	Fail on invalid xAPI Actor (missing or multiple identifiers)
xapi.model.validateAuthority	Fail on invalid xAPI Authority object
xapi.model.validateUriScheme	Fail on invalid xAPI URI property (missing scheme)
xapi.model.validateMbox	Fail on invalid xAPI mbox property (invalid email or missing prefix)
xapi.model.validateLocaleNotUndetermined	Fail on invalid xAPI locale property (locale is undetermined)
xapi.model.validateScaledScore	Fail on invalid xAPI scaledScore property (out of -1 - 1 range)
xapi.model.validateScore	Fail on invalid xAPI Score (raw score is out of min/max range)
xapi.model.validateStatementPlatform	Fail on invalid xAPI context.platform (if present object must be Activity)
xapi.model.validateStatementRevision	Fail on invalid xAPI context.revision (if present object must be Activity)
xapi.model.validateStatementListIds	Fail on invalid xAPI statement List (conflicting statement ids)
xapi.model.validateStatementVerb	Fail on invalid xAPI voided statement (object must be StatemnetReference)
xapi.model.validateUuidVariant	Fail on invalid xAPI UUID property (must be UUID variant 4)

The default value is TRUE for all of the above properties.

xAPI Java Model

The xAPI model can be used by clients that send xAPI data or by servers that receive xAPI data.

Getting started

To use the xAPI Model include the appropriate XML in the dependencies section of your pom.xml, as shown in the following example:

<project>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>getting-started</artifactId>
    <!-- ... -->
    <dependencies>
        <!-- ... -->
        <dependency>
            <groupId>dev.learning.xapi</groupId>
            <artifactId>xapi-model</artifactId>
            <version>1.1.11</version>
        </dependency>
    </dependencies>
</project>

xAPI Model is available in the Maven Central Repository.

Creating a statement

Example:

Statement statement = Statement.builder()

    .agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .verb(Verb.ATTEMPTED)

    .activityObject(o -> o.id("https://example.com/activity/simplestatement")
        .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))

    .build();

Deserializing Statements

The Jackson ObjectMapper can be used to deserialize statements into Java objects.

Example:

String json = """
    {
        "actor":{
            "objectType":"Agent",
            "name":"A N Other",
            "mbox":"mailto:[email protected]"
        },
        "verb":{
            "id":"http://adlnet.gov/expapi/verbs/attempted",
            "display":{
                "und":"attempted"
            }
        },
        "object":{
            "objectType":"Activity",
            "id":"https://example.com/activity/simplestatement",
            "definition":{
                "name":{
                "en":"Simple Statement"
                }
            }
        }
    }""";

Statement statement = objectMapper.readValue(json, Statement.class);

Serializing Statements

The Jackson ObjectMapper can be used to serialize Statement objects into JSON.

Example:

Statement statement = Statement.builder()
    .agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]")).verb(Verb.ATTEMPTED)
    .activityObject(o -> o.id("https://example.com/activity/simplestatement")
        .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))
    .build();

String json = objectMapper.writeValueAsString(statement);

Creating a new statement using an existing statement as template

Example:

Statement passed = Statement.builder()
    .agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]")).verb(Verb.PASSED)
    .activityObject(o -> o.id("https://example.com/activity/simplestatement")
        .definition(d -> d.addName(Locale.ENGLISH, "Simple Statement")))
    .build();

Statement completed = passed.toBuilder().verb(Verb.COMPLETED).build();

Validating Statements

Statements can be validated programmatically.

Example:

Validator validator = Validation.buildDefaultValidatorFactory().getValidator();

Statement statement = Statement.builder()

    .agentActor(a -> a.name("A N Other").mbox("mailto:[email protected]"))

    .activityObject(o -> o.id("https://example.com/xapi/activity/simplestatement"))

    .build();

Set<ConstraintViolation<Statement>> constraintViolations = validator.validate(statement);

System.out.println(constraintViolations)

// Prints [ConstraintViolationImpl{interpolatedMessage='must not be null', propertyPath=verb, rootBeanClass=class dev.learning.xapi.model.Statement, messageTemplate='{jakarta.validation.constraints.NotNull.message}'}]

Statements can also be validated when they are received by a method in a REST controller. The following example requires Spring MVC and the Hibernate Validator.

@PostMapping
public ResponseEntity<Collection<UUID>> postStatements(
    @RequestBody List<@Valid Statement> statements) {

  // Process the statements

  return new ResponseEntity<>(HttpStatus.OK);
}

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