sharding-jdbc中ShardingTracer的作用是什么

sharding-jdbc中ShardingTracer的作用是什么，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

ShardingTracer

incubator-shardingsphere-4.0.0-RC1/sharding-opentracing/src/main/java/org/apache/shardingsphere/opentracing/ShardingTracer.java

@NoArgsConstructor(access = AccessLevel.PRIVATE) public final class ShardingTracer {          private static final String OPENTRACING_TRACER_CLASS_NAME = "org.apache.shardingsphere.opentracing.tracer.class";          /**      * Initialize sharding tracer.      */     public static void init() {         String tracerClassName = System.getProperty(OPENTRACING_TRACER_CLASS_NAME);         Preconditions.checkNotNull(tracerClassName, "Can not find opentracing tracer implementation class via system property `%s`", OPENTRACING_TRACER_CLASS_NAME);         try {             init((Tracer) Class.forName(tracerClassName).newInstance());         } catch (final ReflectiveOperationException ex) {             throw new ShardingException("Initialize opentracing tracer class failure.", ex);         }     }          /**      * Initialize sharding tracer.      *       * @param tracer opentracing tracer      */     public static void init(final Tracer tracer) {         if (!GlobalTracer.isRegistered()) {             GlobalTracer.register(tracer);         }     }          /**      * Get tracer.      *      * @return tracer      */     public static Tracer get() {         return GlobalTracer.get();     } }

• ShardingTracer的init方法会重系统properties中读取OPENTRACING_TRACER_CLASS_NAME的值，然后使用Class.forName加载并创建实例，然后在通过opentracing的GlobalTracer.register进行注册

ShardingTracerTest

incubator-shardingsphere-4.0.0-RC1/sharding-opentracing/src/test/java/org/apache/shardingsphere/opentracing/ShardingTracerTest.java

public final class ShardingTracerTest {          @Before     public void setUp() {         System.setProperty("org.apache.shardingsphere.opentracing.tracer.class", FooTracer.class.getName());         clearGlobalTracer();     }          @After     public void tearDown() {         System.getProperties().remove("org.apache.shardingsphere.opentracing.tracer.class");     }          @Test     public void assertDuplicatedLoading() {         ShardingTracer.init(mock(Tracer.class));         Tracer t1 = ShardingTracer.get();         ShardingTracer.init();         assertEquals(t1, ShardingTracer.get());         ShardingTracer.init(mock(Tracer.class));         assertEquals(t1, ShardingTracer.get());     }          @Test     public void assertTracer() {         ShardingTracer.init();         assertThat((GlobalTracer) ShardingTracer.get(), isA(GlobalTracer.class));         assertTrue(GlobalTracer.isRegistered());         assertThat(ShardingTracer.get(), is(ShardingTracer.get()));     }          @Test(expected = ShardingException.class)     public void assertTracerClassError() {         System.setProperty("org.apache.shardingsphere.opentracing.tracer.class", "com.foo.FooTracer");         ShardingTracer.init();     }          @SneakyThrows     private static void clearGlobalTracer() {         Field tracerField = GlobalTracer.class.getDeclaredField("tracer");         tracerField.setAccessible(true);         tracerField.set(GlobalTracer.class, NoopTracerFactory.create());     } }

• 这里指定了OPENTRACING_TRACER_CLASS_NAME值为FooTracer

FooTracer

incubator-shardingsphere-4.0.0-RC1/sharding-opentracing/src/test/java/org/apache/shardingsphere/opentracing/fixture/FooTracer.java

public final class FooTracer implements Tracer {          @Override     public SpanBuilder buildSpan(final String operationName) {         return null;     }          @Override     public <C> void inject(final SpanContext spanContext, final Format<C> format, final C carrier) {     }          @Override     public <C> SpanContext extract(final Format<C> format, final C carrier) {         return null;     }          @Override     public ActiveSpan activeSpan() {         return null;     }          @Override     public ActiveSpan makeActive(final Span span) {         return null;     } }

• FooTracer实现了Tracer接口，这里为空实现

小结

ShardingTracer的init方法会重系统properties中读取OPENTRACING_TRACER_CLASS_NAME的值，然后使用Class.forName加载并创建实例，然后在通过opentracing的GlobalTracer.register进行注册

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