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本文主要研究一下Elasticsearch RestClient的NodeSelector

NodeSelector

elasticsearch-7.0.1/client/rest/src/main/java/org/elasticsearch/client/NodeSelector.java

public interface NodeSelector {
    /**
     * Select the {@link Node}s to which to send requests. This is called with
     * a mutable {@link Iterable} of {@linkplain Node}s in the order that the
     * rest client would prefer to use them and implementers should remove
     * nodes from the that should not receive the request. Implementers may
     * iterate the nodes as many times as they need.
     * <p>
     * This may be called twice per request: first for "living" nodes that
     * have not been blacklisted by previous errors. If the selector removes
     * all nodes from the list or if there aren't any living nodes then the
     * {@link RestClient} will call this method with a list of "dead" nodes.
     * <p>
     * Implementers should not rely on the ordering of the nodes.
     */
    void select(Iterable<Node> nodes);
    /*
     * We were fairly careful with our choice of Iterable here. The caller has
     * a List but reordering the list is likely to break round robin. Luckily
     * Iterable doesn't allow any reordering.
     */

    /**
     * Selector that matches any node.
     */
    NodeSelector ANY = new NodeSelector() {
        @Override
        public void select(Iterable<Node> nodes) {
            // Intentionally does nothing
        }

        @Override
        public String toString() {
            return "ANY";
        }
    };

    /**
     * Selector that matches any node that has metadata and doesn't
     * have the {@code master} role OR it has the data {@code data}
     * role.
     */
    NodeSelector SKIP_DEDICATED_MASTERS = new NodeSelector() {
        @Override
        public void select(Iterable<Node> nodes) {
            for (Iterator<Node> itr = nodes.iterator(); itr.hasNext();) {
                Node node = itr.next();
                if (node.getRoles() == null) continue;
                if (node.getRoles().isMasterEligible()
                        && false == node.getRoles().isData()
                        && false == node.getRoles().isIngest()) {
                    itr.remove();
                }
            }
        }

        @Override
        public String toString() {
            return "SKIP_DEDICATED_MASTERS";
        }
    };
}

• NodeSelector接口定义了select方法，它接收mutable的Iterable，然后具体实现会选择性删除node；它定义了ANY、SKIP_DEDICATED_MASTERS两个匿名实现类，其中ANY的select方法不做任何操作；SKIP_DEDICATED_MASTERS的select方法会删除date为false、ingest为false的master node；除此之外还有HasAttributeNodeSelector、PreferHasAttributeNodeSelector两个实现类

HasAttributeNodeSelector

elasticsearch-7.0.1/client/rest/src/main/java/org/elasticsearch/client/HasAttributeNodeSelector.java

public final class HasAttributeNodeSelector implements NodeSelector {
    private final String key;
    private final String value;

    public HasAttributeNodeSelector(String key, String value) {
        this.key = key;
        this.value = value;
    }

    @Override
    public void select(Iterable<Node> nodes) {
        Iterator<Node> itr = nodes.iterator();
        while (itr.hasNext()) {
            Map<String, List<String>> allAttributes = itr.next().getAttributes();
            if (allAttributes == null) continue;
            List<String> values = allAttributes.get(key);
            if (values == null || false == values.contains(value)) {
                itr.remove();
            }
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        HasAttributeNodeSelector that = (HasAttributeNodeSelector) o;
        return Objects.equals(key, that.key) &&
                Objects.equals(value, that.value);
    }

    @Override
    public int hashCode() {
        return Objects.hash(key, value);
    }

    @Override
    public String toString() {
        return key + "=" + value;
    }
}

• HasAttributeNodeSelector实现了NodeSelector接口，其构造器接收key、value参数，其select方法会删除node的attributes没有该key或者该key对应的value为null的node

PreferHasAttributeNodeSelector

elasticsearch-7.0.1/client/rest/src/main/java/org/elasticsearch/client/PreferHasAttributeNodeSelector.java

public final class PreferHasAttributeNodeSelector implements NodeSelector {
    private final String key;
    private final String value;

    public PreferHasAttributeNodeSelector(String key, String value) {
        this.key = key;
        this.value = value;
    }

    @Override
    public void select(Iterable<Node> nodes) {
        boolean foundAtLeastOne = false;

        for (Node node : nodes) {
            Map<String, List<String>> attributes = node.getAttributes();

            if (attributes == null) {
                continue;
            }

            List<String> values = attributes.get(key);

            if (values == null) {
                continue;
            }

            if (values.contains(value)) {
                foundAtLeastOne = true;
                break;
            }
        }

        if (foundAtLeastOne) {
            Iterator<Node> nodeIterator = nodes.iterator();
            while (nodeIterator.hasNext()) {
                Map<String, List<String>> attributes = nodeIterator.next().getAttributes();

                if (attributes == null) {
                    continue;
                }

                List<String> values = attributes.get(key);

                if (values == null || !values.contains(value)) {
                    nodeIterator.remove();
                }
            }
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        PreferHasAttributeNodeSelector that = (PreferHasAttributeNodeSelector) o;
        return Objects.equals(key, that.key) &&
            Objects.equals(value, that.value);
    }

    @Override
    public int hashCode() {
        return Objects.hash(key, value);
    }

    @Override
    public String toString() {
        return key + "=" + value;
    }
}

• PreferHasAttributeNodeSelector实现了NodeSelector接口，其构造器接收key、value参数，其select方法会先遍历nodes设置foundAtLeastOne，如果foundAtLeastOne为true才会删除node的attributes没有该key或者该key对应的value为null的node

小结

• NodeSelector接口定义了select方法，它接收mutable的Iterable，然后具体实现会选择性删除node；它定义了ANY、SKIP_DEDICATED_MASTERS两个匿名实现类，其中ANY的select方法不做任何操作；SKIP_DEDICATED_MASTERS的select方法会删除date为false、ingest为false的master node
• HasAttributeNodeSelector实现了NodeSelector接口，其构造器接收key、value参数，其select方法会删除node的attributes没有该key或者该key对应的value为null的node
• PreferHasAttributeNodeSelector实现了NodeSelector接口，其构造器接收key、value参数，其select方法会先遍历nodes设置foundAtLeastOne，如果foundAtLeastOne为true才会删除node的attributes没有该key或者该key对应的value为null的node

doc

• Node selector