序
本文主要研究一下sentinel的DefaultSlotsChainBuilder
DefaultSlotsChainBuilder
com/alibaba/csp/sentinel/slots/DefaultSlotsChainBuilder.java
public class DefaultSlotsChainBuilder implements SlotsChainBuilder {
@Override
public ProcessorSlotChain build() {
ProcessorSlotChain chain = new DefaultProcessorSlotChain();
chain.addLast(new NodeSelectorSlot());
chain.addLast(new ClusterBuilderSlot());
chain.addLast(new LogSlot());
chain.addLast(new StatisticSlot());
chain.addLast(new SystemSlot());
chain.addLast(new AuthoritySlot());
chain.addLast(new FlowSlot());
chain.addLast(new DegradeSlot());
return chain;
}
}- 实现build方法，返回DefaultProcessorSlotChain，通过它addLast方法构造链式调用
DefaultProcessorSlotChain
com/alibaba/csp/sentinel/slotchain/DefaultProcessorSlotChain.java
public class DefaultProcessorSlotChain extends ProcessorSlotChain {
AbstractLinkedProcessorSlot first = new AbstractLinkedProcessorSlot- 主要有两个属性，一个是first，一个是end，它们是AbstractLinkedProcessorSlot类型
- 方法主要有addFirst，addLast，setNext
- 这里默认设置了first，之后主要是通过getNext方法来开启链式调用，getNext方法返回的是first的next
AbstractLinkedProcessorSlot
com/alibaba/csp/sentinel/slotchain/AbstractLinkedProcessorSlot.java
public abstract class AbstractLinkedProcessorSlot implements ProcessorSlot {
private AbstractLinkedProcessorSlot next = null;
@Override
public void fireEntry(Context context, ResourceWrapper resourceWrapper, Object obj, int count, Object... args)
throws Throwable {
if (next != null) {
next.transformEntry(context, resourceWrapper, obj, count, args);
}
}
@SuppressWarnings("unchecked")
void transformEntry(Context context, ResourceWrapper resourceWrapper, Object o, int count, Object... args)
throws Throwable {
T t = (T)o;
entry(context, resourceWrapper, t, count, args);
}
@Override
public void fireExit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
if (next != null) {
next.exit(context, resourceWrapper, count, args);
}
}
public AbstractLinkedProcessorSlot getNext() {
return next;
}
public void setNext(AbstractLinkedProcessorSlot next) {
this.next = next;
}
} - AbstractLinkedProcessorSlot是所有slot的基类，有个next属性，用来标识下一个slot
- entry是整个链式调用的入口，默认是会触发fireEntry，通过判断next不为null，则调用next的transformEntry，进而调用next的entry方法
- 子类的entry方法会做一些前置校验工作，通过之后调用fireEntry方法，进而完成整个链式调用
小结
sentinel使用了责任链模式来进行各种slot逻辑的执行，其构建是通过DefaultSlotsChainBuilder来进行build。
doc
- slotchain