设计模式课程 设计模式精讲 25-3 责任链模式源码解析

1　　　　源码解析

1.1　　　　源码解析1（Servlet过滤器的应用）

 

 

 

 

1　　　　源码解析

1.1　　　　源码解析1（Servlet过滤器的应用）

重点讲解：

1　　filterchain中有很多的filter，filter按照一定的顺序组装成一个链条，可以理解成责任链模式。

2　　每次filter 执行dofilter方法的时候，都会调到filterchain，filterchain又会执行下一个filter的dofiltet方法，这样实现了循环调用dofilter方法（见filterchain和filter实现类标红部分）。

Filter：

//
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package javax.servlet;

import java.io.IOException;

public interface Filter {
    void init(FilterConfig var1) throws ServletException;

    void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;

    void destroy();
}

 FilterChain：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
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package javax.servlet;

import java.io.IOException;

public interface FilterChain {
    void doFilter(ServletRequest var1, ServletResponse var2) throws IOException, ServletException;
}

Filter实现类：

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// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
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package ch.qos.logback.classic.selector.servlet;

import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.selector.ContextJNDISelector;
import ch.qos.logback.classic.selector.ContextSelector;
import ch.qos.logback.classic.util.ContextSelectorStaticBinder;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.slf4j.LoggerFactory;

public class LoggerContextFilter implements Filter {
    public LoggerContextFilter() {
    }

    public void destroy() {
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        LoggerContext lc = (LoggerContext)LoggerFactory.getILoggerFactory();
        ContextSelector selector = ContextSelectorStaticBinder.getSingleton().getContextSelector();
        ContextJNDISelector sel = null;
        if (selector instanceof ContextJNDISelector) {
            sel = (ContextJNDISelector)selector;
            sel.setLocalContext(lc);
        }

        try {
            chain.doFilter(request, response);
        } finally {
            if (sel != null) {
                sel.removeLocalContext();
            }

        }

    }

    public void init(FilterConfig arg0) throws ServletException {
    }
}

FilterChain实现类：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
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package org.springframework.mock.web;

import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.Servlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

public class MockFilterChain implements FilterChain {
    private ServletRequest request;
    private ServletResponse response;
    private final List<Filter> filters;
    private Iterator<Filter> iterator;

    public MockFilterChain() {
        this.filters = Collections.emptyList();
    }

    public MockFilterChain(Servlet servlet) {
        this.filters = initFilterList(servlet);
    }

    public MockFilterChain(Servlet servlet, Filter... filters) {
        Assert.notNull(filters, "filters cannot be null");
        Assert.noNullElements(filters, "filters cannot contain null values");
        this.filters = initFilterList(servlet, filters);
    }

    private static List<Filter> initFilterList(Servlet servlet, Filter... filters) {
        Filter[] allFilters = (Filter[])ObjectUtils.addObjectToArray(filters, new MockFilterChain.ServletFilterProxy(servlet));
        return Arrays.asList(allFilters);
    }

    public ServletRequest getRequest() {
        return this.request;
    }

    public ServletResponse getResponse() {
        return this.response;
    }

    public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
        Assert.notNull(request, "Request must not be null");
        Assert.notNull(response, "Response must not be null");
        if (this.request != null) {
            throw new IllegalStateException("This FilterChain has already been called!");
        } else {
            if (this.iterator == null) {
                this.iterator = this.filters.iterator();
            }

            if (this.iterator.hasNext()) {
                Filter nextFilter = (Filter)this.iterator.next();
                nextFilter.doFilter(request, response, this);
            }

            this.request = request;
            this.response = response;
        }
    }

    public void reset() {
        this.request = null;
        this.response = null;
        this.iterator = null;
    }

    private static class ServletFilterProxy implements Filter {
        private final Servlet delegateServlet;

        private ServletFilterProxy(Servlet servlet) {
            Assert.notNull(servlet, "servlet cannot be null");
            this.delegateServlet = servlet;
        }

        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            this.delegateServlet.service(request, response);
        }

        public void init(FilterConfig filterConfig) throws ServletException {
        }

        public void destroy() {
        }

        public String toString() {
            return this.delegateServlet.toString();
        }
    }
}