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What is the role of ShardingTracer in sharding-jdbc, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

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 ();}}

The init method of ShardingTracer reads the value of OPENTRACING_TRACER_CLASS_NAME in the system properties, then loads and creates the instance using Class.forName, and then registers in the GlobalTracer.register through opentracing

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 ());}}

Here the OPENTRACING_TRACER_CLASS_ name value is specified as 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 implements the Tracer interface, here is a null implementation

Summary

The init method of ShardingTracer reads the value of OPENTRACING_TRACER_CLASS_NAME in the system properties, then loads and creates the instance using Class.forName, and then registers in the GlobalTracer.register through opentracing

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