GraphQL Java - Instrumentation

Instrumentation拦截器

通过实现Instrumentation接口，可以观察一个query的执行，或修改运行期的行为。

最常见的用途是进行性能监控，和自定义日志记录，但它也可以用于完成其他任务。

创建GraphQL对象时，可以绑定相关的Instrumentation实现。

        GraphQL.newGraphQL(schema).instrumentation(new TracingInstrumentation()).build();

自定义Instrumentation拦截器

Instrumentation实现类需要实现"begin"开头的方法。这个方法会在查询执行的过程中，在每个步骤开始之前被调用。

每个回调方法都必须返回一个非空的InstrumentationContext对象，这个对象在本执行步骤完成时会被回调，并告知是否调用成功或是出错（可以获取Throwable对象）。

下面的示例中，给出了一个自定义的Instrumentation拦截器。可以用来测量执行过程的整体执行时间，并将结果存入一个有状态的对象当中。

    class CustomInstrumentationState implements InstrumentationState {private Map<String, Object> anyStateYouLike = new HashMap<>();void recordTiming(String key, long time) {anyStateYouLike.put(key, time);}}class CustomInstrumentation extends SimpleInstrumentation {@Overridepublic InstrumentationState createState() {//// instrumentation state is passed during each invocation of an Instrumentation method// and allows you to put stateful data away and reference it during the query execution//return new CustomInstrumentationState();}@Overridepublic InstrumentationContext<ExecutionResult> beginExecution(InstrumentationExecutionParameters parameters) {long startNanos = System.nanoTime();return new SimpleInstrumentationContext<ExecutionResult>() {@Overridepublic void onCompleted(ExecutionResult result, Throwable t) {CustomInstrumentationState state = parameters.getInstrumentationState();state.recordTiming(parameters.getQuery(), System.nanoTime() - startNanos);}};}@Overridepublic DataFetcher<?> instrumentDataFetcher(DataFetcher<?> dataFetcher, InstrumentationFieldFetchParameters parameters) {//// this allows you to intercept the data fetcher used to fetch a field and provide another one, perhaps// that enforces certain behaviours or has certain side effects on the data//return dataFetcher;}@Overridepublic CompletableFuture<ExecutionResult> instrumentExecutionResult(ExecutionResult executionResult, InstrumentationExecutionParameters parameters) {//// this allows you to instrument the execution result some how.  For example the Tracing support uses this to put// the `extensions` map of data in place//return CompletableFuture.completedFuture(executionResult);}}

链式Instrumentation拦截器

可以使用ChainedInstrumentation类，将多个Instrumentation对象进行聚合。ChainedInstrumentation类接收一个Instrumentation对象列表参数，然后按照它们定义的顺序依次调用。

        List<Instrumentation> chainedList = new ArrayList<>();chainedList.add(new FooInstrumentation());chainedList.add(new BarInstrumentation());ChainedInstrumentation chainedInstrumentation = new ChainedInstrumentation(chainedList);GraphQL.newGraphQL(schema).instrumentation(chainedInstrumentation).build();

字段验证Instrumentation

FieldValidationInstrumentation拦截器，可以在执行查询前，校验字段和字段参数。如果校验失败，那么执行过程将终止，error信息添加到查询的result当中。

可以自定义FieldValidation的实现，或直接使用SimpleFieldValidation类来为每个字段增加校验规则。

        ExecutionPath fieldPath = ExecutionPath.parse("/user");FieldValidation fieldValidation = new SimpleFieldValidation().addRule(fieldPath, new BiFunction<FieldAndArguments, FieldValidationEnvironment, Optional<GraphQLError>>() {@Overridepublic Optional<GraphQLError> apply(FieldAndArguments fieldAndArguments, FieldValidationEnvironment environment) {String nameArg = fieldAndArguments.getFieldArgument("name");if (nameArg.length() > 255) {return Optional.of(environment.mkError("Invalid user name", fieldAndArguments));}return Optional.empty();}});FieldValidationInstrumentation instrumentation = new FieldValidationInstrumentation(fieldValidation);GraphQL.newGraphQL(schema).instrumentation(instrumentation).build();