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本文主要研究一下nacos client的ConfigFilterChainManager

IConfigFilterChain

nacos-1.1.3/api/src/main/java/com/alibaba/nacos/api/config/filter/IConfigFilterChain.java

public interface IConfigFilterChain {
    /**
     * Filter aciton
     *
     * @param request  request
     * @param response response
     * @throws NacosException NacosException
     */
    void doFilter(IConfigRequest request, IConfigResponse response) throws NacosException;

}

• IConfigFilterChain接口定义了doFilter方法

ConfigFilterChainManager

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/config/filter/impl/ConfigFilterChainManager.java

public class ConfigFilterChainManager implements IConfigFilterChain {

    private List<IConfigFilter> filters = Lists.newArrayList();

    public synchronized ConfigFilterChainManager addFilter(IConfigFilter filter) {
        // 根据order大小顺序插入
        int i = 0;
        while (i < this.filters.size()) {
            IConfigFilter currentValue = this.filters.get(i);
            if (currentValue.getFilterName().equals(filter.getFilterName())) {
                break;
            }
            if (filter.getOrder() >= currentValue.getOrder() && i < this.filters.size()) {
                i++;
            } else {
                this.filters.add(i, filter);
                break;
            }
        }

        if (i == this.filters.size()) {
            this.filters.add(i, filter);
        }
        return this;
    }

    @Override
    public void doFilter(IConfigRequest request, IConfigResponse response) throws NacosException {
        new VirtualFilterChain(this.filters).doFilter(request, response);
    }

    //......
}

• ConfigFilterChainManager实现了IConfigFilterChain接口，其doFilter方法使用filters创建VirtualFilterChain，然后执行其doFilter方法；它提供了addFilter方法，可以根据filter的order顺序添加到filters中

VirtualFilterChain

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/config/filter/impl/ConfigFilterChainManager.java

public class ConfigFilterChainManager implements IConfigFilterChain {

    //......

    private static class VirtualFilterChain implements IConfigFilterChain {

        private final List<? extends IConfigFilter> additionalFilters;

        private int currentPosition = 0;

        public VirtualFilterChain(List<? extends IConfigFilter> additionalFilters) {
            this.additionalFilters = additionalFilters;
        }

        @Override
        public void doFilter(final IConfigRequest request, final IConfigResponse response) throws NacosException {
            if (this.currentPosition != this.additionalFilters.size()) {
                this.currentPosition++;
                IConfigFilter nextFilter = this.additionalFilters.get(this.currentPosition - 1);
                nextFilter.doFilter(request, response, this);
            }
        }
    }

    //......
}

• VirtualFilterChain实现了IConfigFilterChain接口，它维护了一个currentPosition属性，其doFilter方法会在currentPosition不等于additionalFilters.size()时递增currentPosition，然后取出nextFilter把自己作为参数去执行doFilter

IConfigFilter

nacos-1.1.3/api/src/main/java/com/alibaba/nacos/api/config/filter/IConfigFilter.java

public interface IConfigFilter {
    /**
     * Init
     *
     * @param filterConfig Filter Config
     */
    void init(IFilterConfig filterConfig);

    /**
     * do filter
     *
     * @param request     request
     * @param response    response
     * @param filterChain filter Chain
     * @throws NacosException exception
     */
    void doFilter(IConfigRequest request, IConfigResponse response, IConfigFilterChain filterChain)
            throws NacosException;

    /**
     * deploy
     */
    void deploy();

    /**
     * Get order
     *
     * @return order number
     */
    int getOrder();

    /**
     * Get filterName
     *
     * @return filter name
     */
    String getFilterName();

}

• IConfigFilter接口的doFilter方法的第三个参数为IConfigFilterChain；其实现类执行完自己的处理之后，如果要继续，可以执行filterChain.doFilter来继续交给下面的filter处理

小结

ConfigFilterChainManager实现了IConfigFilterChain接口，其doFilter方法使用filters创建VirtualFilterChain，然后执行其doFilter方法；它提供了addFilter方法，可以根据filter的order顺序添加到filters中

doc

• ConfigFilterChainManager