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TracerConverter (Wrapper) support (#8)
* Check license header as part of build. * Initial rough version of Wrapper support (without @priority order). * Isolate Resolver concept from Wrapper changes. * Add a short notice about tracer wrappers. * Move warning (about wrapping) from TracerResolver into Wrappers class. * Add missing license header. * Add braces around if. * Rename TracerWrapperProvider to TracerConverter. * Outline potential 'wrapper' use of the tracer converter * Update JavaDoc example when converter can recieve a null tracer. * Don't call converter if resolved Tracer is null. * Just break out of the loop (thanks @objectiser) * Document priority of TracerResolver. * Document priority concept in javadoc of TracerConverter as well. * Don't begin loop in the first place if resolved == null. * Fix illegal JavaDoc. * Add unit-tests for TracerConverter. Including priority-order, returning nulls and throwing exceptions.
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src/main/java/io/opentracing/contrib/tracerresolver/TracerConverter.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,57 @@ | ||
| /* | ||
| * Copyright 2017 The OpenTracing Authors | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| package io.opentracing.contrib.tracerresolver; | ||
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| import io.opentracing.Tracer; | ||
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| /** | ||
| * Function converting an existing {@link Tracer}. | ||
| * <p> | ||
| * This can be useful for <em>wrapping</em> tracers: | ||
| * <pre><code> | ||
| * public final class FooWrapperConverter implements TracerConverter { | ||
| * public Tracer convert(Tracer existingTracer) { | ||
| * return new FooTracerWrapper(existingTracer); | ||
| * } | ||
| * } | ||
| * </code></pre> | ||
| * <p> | ||
| * If there are multiple {@linkplain TracerConverter} implementations resolved, | ||
| * they will be applied in the order of their {@literal @}Priority annotation: | ||
| * <ol> | ||
| * <li>First, non-negative priority is applied in natural order (e.g. {@code 0}, {@code 1}, {@code 2}, ...).</li> | ||
| * <li>Next, objects without <code>{@literal @}Priority</code> annotation are applied | ||
| * by assigning a <em>default priority</em> of {@link Integer#MAX_VALUE}.</li> | ||
| * <li>Finally, negative priority is applied in reverse-natural order (e.g. {@code -1}, {@code -2}, {@code -3}, ...).</li> | ||
| * </ol> | ||
| * <p> | ||
| * The order of objects with equal (implicit) priority is undefined. | ||
| * | ||
| * @author Sjoerd Talsma | ||
| */ | ||
| public interface TracerConverter { | ||
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| /** | ||
| * Function that converts a {@link Tracer}. | ||
| * <p> | ||
| * It may either manipulate the tracer or return an entirely new {@linkplain Tracer} instance. | ||
| * | ||
| * @param existingTracer The existing tracer to be converted. | ||
| * @return The converted tracer. | ||
| */ | ||
| Tracer convert(Tracer existingTracer); | ||
|
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| } |
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93
src/test/java/io/opentracing/contrib/tracerresolver/TracerConverterTest.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,93 @@ | ||
| /* | ||
| * Copyright 2017 The OpenTracing Authors | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| package io.opentracing.contrib.tracerresolver; | ||
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| import org.junit.After; | ||
| import org.junit.Before; | ||
| import org.junit.Test; | ||
|
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| import java.io.File; | ||
| import java.io.IOException; | ||
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| import static io.opentracing.contrib.tracerresolver.TracerResolverTest.writeServiceFile; | ||
| import static org.hamcrest.MatcherAssert.assertThat; | ||
| import static org.hamcrest.Matchers.*; | ||
|
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| public class TracerConverterTest { | ||
| private static final File SERVICES_DIR = new File("target/test-classes/META-INF/services/"); | ||
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| @After | ||
| public void cleanServiceFiles() throws IOException { | ||
| new File(SERVICES_DIR, TracerResolver.class.getName()).delete(); | ||
| new File(SERVICES_DIR, TracerConverter.class.getName()).delete(); | ||
| } | ||
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| @Before | ||
| @After | ||
| public void resetTracerResolver() { | ||
| Mocks.calledConverterTypes.clear(); | ||
| TracerResolver.reload(); | ||
| } | ||
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| @Test | ||
| public void testConverterNotCalledWhenNothingRegistered() throws IOException { | ||
| writeServiceFile(TracerConverter.class, Mocks.IdentityConverter.class); | ||
| assertThat("No tracer should be resolved", TracerResolver.resolveTracer(), is(nullValue())); | ||
| assertThat("No converter should be called", Mocks.calledConverterTypes, hasSize(0)); | ||
| } | ||
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| @Test | ||
| public void testTrivialConverterExample() throws IOException { | ||
| writeServiceFile(TracerResolver.class, Mocks.MockTracerResolver.class); | ||
| writeServiceFile(TracerConverter.class, Mocks.IdentityConverter.class); | ||
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| assertThat("Tracer must be resolved", TracerResolver.resolveTracer(), instanceOf(Mocks.ResolvedTracer.class)); | ||
| assertThat("Converter must be called", Mocks.calledConverterTypes, contains((Class) Mocks.IdentityConverter.class)); | ||
| } | ||
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| @Test | ||
| public void testConverterNotCalledWhenProviderReturnsNull() throws IOException { | ||
| writeServiceFile(TracerResolver.class, Mocks.NullTracerResolver.class); | ||
| writeServiceFile(TracerConverter.class, Mocks.IdentityConverter.class); | ||
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| assertThat("Resolved tracer", TracerResolver.resolveTracer(), is(nullValue())); | ||
| assertThat("No converter should be called", Mocks.calledConverterTypes, hasSize(0)); | ||
| } | ||
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| @Test | ||
| public void testConverterThrowingException() throws IOException { | ||
| writeServiceFile(TracerResolver.class, Mocks.MockTracerResolver.class); | ||
| // although identity converter is listed first, the @Priority(5) should let throwing converter be called first! | ||
| writeServiceFile(TracerConverter.class, Mocks.IdentityConverter.class, Mocks.Prio5_ThrowingConverter.class); | ||
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| assertThat("Resolved tracer", TracerResolver.resolveTracer(), instanceOf(Mocks.ResolvedTracer.class)); | ||
| assertThat("Continue after exception", Mocks.calledConverterTypes, hasSize(2)); | ||
| assertThat("Predictable order", Mocks.calledConverterTypes, | ||
| contains((Class) Mocks.Prio5_ThrowingConverter.class, Mocks.IdentityConverter.class)); | ||
| } | ||
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| @Test | ||
| public void testconvertToNull() throws IOException { | ||
| writeServiceFile(TracerResolver.class, Mocks.MockTracerResolver.class); | ||
| // although identity converter is listed first, the @Priority(10) should let convertToNull be called first! | ||
| writeServiceFile(TracerConverter.class, Mocks.IdentityConverter.class, Mocks.Prio10_ConvertToNull.class); | ||
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| assertThat("Tracer after conversion(s)", TracerResolver.resolveTracer(), is(nullValue())); | ||
| assertThat("Second converter shouldn't be called with <null>", Mocks.calledConverterTypes, hasSize(1)); | ||
| assertThat("Prioritized converter", Mocks.calledConverterTypes, contains((Class) Mocks.Prio10_ConvertToNull.class)); | ||
| } | ||
|
|
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| } |
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