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。
incubator-shardingsphere-4.0.0-RC1/sharding-opentracing/src/main/java/org/apache/shardingsphere/opentracing/ShardingTracer.java
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@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
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
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
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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原文链接：https://my.oschina.net/go4it/blog/3084429
