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  void inject(final SpanContext spanContext, final Format format, final C carrier) {    }        @Override    public  SpanContext extract(final Format 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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