詳解spring security filter的工作原理

發(fā)布時間：2020-08-22 15:44:21 來源：腳本之家閱讀：228 作者：流浪的神明欄目：編程語言

這篇文章介紹filter的工作原理。配置方式為xml。

Filter如何進(jìn)入執(zhí)行邏輯的

初始配置：

 <filter>
  <filter-name>springSecurityFilterChain</filter-name>
  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
 </filter>

 <filter-mapping>
  <filter-name>springSecurityFilterChain</filter-name>
  <url-pattern>/*</url-pattern>
 </filter-mapping>

DelegatingFilterProxy這個類繼承了GenericFilterBean，GenericFilterBean實(shí)現(xiàn)了Filter接口。

這個配置是一切的開始，配置完這個之后，在啟動項(xiàng)目的時候會執(zhí)行Filterd的初始化方法：

@Override
  public final void init(FilterConfig filterConfig) throws ServletException {
    Assert.notNull(filterConfig, "FilterConfig must not be null");
    if (logger.isDebugEnabled()) {
      logger.debug("Initializing filter '" + filterConfig.getFilterName() + "'");
    }

    this.filterConfig = filterConfig;

    // Set bean properties from init parameters.
    PropertyValues pvs = new FilterConfigPropertyValues(filterConfig, this.requiredProperties);
    if (!pvs.isEmpty()) {
      try {
        BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
        ResourceLoader resourceLoader = new ServletContextResourceLoader(filterConfig.getServletContext());
        Environment env = this.environment;
        if (env == null) {
          env = new StandardServletEnvironment();
        }
        bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, env));
        initBeanWrapper(bw);
        bw.setPropertyValues(pvs, true);
      }
      catch (BeansException ex) {
        String msg = "Failed to set bean properties on filter '" +
          filterConfig.getFilterName() + "': " + ex.getMessage();
        logger.error(msg, ex);
        throw new NestedServletException(msg, ex);
      }
    }

    // Let subclasses do whatever initialization they like.
    initFilterBean(); // 這個方法

    if (logger.isDebugEnabled()) {
      logger.debug("Filter '" + filterConfig.getFilterName() + "' configured successfully");
    }
  }

在初始化方法中，會執(zhí)行初始化Filter的方法initFilterBean。這個方法的實(shí)現(xiàn)在DelegatingFilterProxy中：

protected void initFilterBean() throws ServletException {
    synchronized (this.delegateMonitor) {
      if (this.delegate == null) {
        // If no target bean name specified, use filter name.
        if (this.targetBeanName == null) {
          this.targetBeanName = getFilterName();
        }
        // Fetch Spring root application context and initialize the delegate early,
        // if possible. If the root application context will be started after this
        // filter proxy, we'll have to resort to lazy initialization.
        WebApplicationContext wac = findWebApplicationContext();
        if (wac != null) {
          this.delegate = initDelegate(wac); //這個方法
        }
      }
    }
  }

在這個初始化方法中又調(diào)用initDelegate方法進(jìn)行初始化：

protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
    String targetBeanName = getTargetBeanName();
    Assert.state(targetBeanName != null, "No target bean name set");
    Filter delegate = wac.getBean(targetBeanName, Filter.class);
    if (isTargetFilterLifecycle()) {
      delegate.init(getFilterConfig());
    }
    return delegate;
  }

在這個方法中，先獲取targetBeanName，這個名字是構(gòu)造方法中賦值的：

public DelegatingFilterProxy(String targetBeanName, @Nullable WebApplicationContext wac) {
    Assert.hasText(targetBeanName, "Target Filter bean name must not be null or empty");
    this.setTargetBeanName(targetBeanName);
    this.webApplicationContext = wac;
    if (wac != null) {
      this.setEnvironment(wac.getEnvironment());
    }
  }

這個名字就是web.xml中配置的名字springSecurityFilterChain：

 <filter>
  <filter-name>springSecurityFilterChain</filter-name>
  <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
 </filter>

springSecurityFilterChain是固定不能改的，如果改了啟動時就會報錯，這是spring 啟動時內(nèi)置的一個bean，這個bean實(shí)際是FilterChainProxy。

這樣一個Filter就初始化話好了，過濾器chain也初始化好了。

當(dāng)一個請求進(jìn)來的時候，會進(jìn)入FilterChainProxy執(zhí)行doFilter方法：

public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException {
    boolean clearContext = request.getAttribute(FILTER_APPLIED) == null;
    if (clearContext) {
      try {
        request.setAttribute(FILTER_APPLIED, Boolean.TRUE);
        doFilterInternal(request, response, chain);
      }
      finally {
        SecurityContextHolder.clearContext();
        request.removeAttribute(FILTER_APPLIED);
      }
    }
    else {
      doFilterInternal(request, response, chain);
    }
  }

先獲取所有的Filter，然后執(zhí)行doFilterInternal方法：

private void doFilterInternal(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException {

    FirewalledRequest fwRequest = firewall
        .getFirewalledRequest((HttpServletRequest) request);
    HttpServletResponse fwResponse = firewall
        .getFirewalledResponse((HttpServletResponse) response);

    List<Filter> filters = getFilters(fwRequest);

    if (filters == null || filters.size() == 0) {
      if (logger.isDebugEnabled()) {
        logger.debug(UrlUtils.buildRequestUrl(fwRequest)
            + (filters == null ? " has no matching filters"
                : " has an empty filter list"));
      }

      fwRequest.reset();

      chain.doFilter(fwRequest, fwResponse);

      return;
    }

    // 最終執(zhí)行下面的這些代碼
    VirtualFilterChain vfc = new VirtualFilterChain(fwRequest, chain, filters);
    vfc.doFilter(fwRequest, fwResponse);
  }

VirtualFilterChain是一個匿名內(nèi)部類：

private static class VirtualFilterChain implements FilterChain {
    private final FilterChain originalChain;
    private final List<Filter> additionalFilters;
    private final FirewalledRequest firewalledRequest;
    private final int size;
    private int currentPosition = 0;

    private VirtualFilterChain(FirewalledRequest firewalledRequest,
        FilterChain chain, List<Filter> additionalFilters) {
      this.originalChain = chain;
      this.additionalFilters = additionalFilters;
      this.size = additionalFilters.size();
      this.firewalledRequest = firewalledRequest;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response)
        throws IOException, ServletException {
      if (currentPosition == size) {
        if (logger.isDebugEnabled()) {
          logger.debug(UrlUtils.buildRequestUrl(firewalledRequest)
              + " reached end of additional filter chain; proceeding with original chain");
        }

        // Deactivate path stripping as we exit the security filter chain
        this.firewalledRequest.reset();

        originalChain.doFilter(request, response);
      }
      else {
        currentPosition++;

        Filter nextFilter = additionalFilters.get(currentPosition - 1);

        if (logger.isDebugEnabled()) {
          logger.debug(UrlUtils.buildRequestUrl(firewalledRequest)
              + " at position " + currentPosition + " of " + size
              + " in additional filter chain; firing Filter: '"
              + nextFilter.getClass().getSimpleName() + "'");
        }

        nextFilter.doFilter(request, response, this);
      }
    }
  }

filter集合執(zhí)行的邏輯在VirtualFilterChain的doFilter方法中。

filter是如何執(zhí)行的

上面說了怎么才能進(jìn)入filter的執(zhí)行邏輯，下面說一下filter到底怎么執(zhí)行，為什么一個

在VirtualFilterChain的doFilter方法可以執(zhí)行所有的filter。

下面寫一個例子，模擬filter的執(zhí)行邏輯。
定義FilterChain接口、Filter接口：

public interface Filter {

  void doFilter(String username, int age, FilterChain filterChain);
}

public interface FilterChain {

  void doFilter(String username, int age);
}

定義兩個Filter實(shí)現(xiàn)：

public class NameFilter implements Filter {

  @Override
  public void doFilter(String username, int age, FilterChain filterChain) {

    username = username + 1;
    System.out.println("username: " + username + "  age: " + age);
    System.out.println("正在執(zhí)行：NameFilter");
    filterChain.doFilter(username, age);
  }
}

public class AgeFilter implements Filter {

  @Override
  public void doFilter(String username, int age, FilterChain filterChain) {

    age += 10;
    System.out.println("username: " + username + "  age: " + age);
    System.out.println("正在執(zhí)行：AgeFilter");
    filterChain.doFilter(username, age);
  }
}

定義一個FilterChain實(shí)現(xiàn)：

public class FilterChainProxy implements FilterChain {


  private int position = 0;
  private int size = 0;
  private List<Filter> filterList = new ArrayList<>();

  public void addFilter(Filter filter) {

    filterList.add(filter);
    size++;
  }

  @Override
  public void doFilter(String username, int age) {

    if (size == position) {
      System.out.println("過濾器鏈執(zhí)行結(jié)束");
    } else {

      Filter filter = filterList.get(position);
      position++;
      filter.doFilter(username, age, this);
    }
  }
}

測試Filter實(shí)現(xiàn)：

public class FilterTest {

  public static void main(String[] args) {

    FilterChainProxy proxy = new FilterChainProxy();
    proxy.addFilter(new NameFilter());
    proxy.addFilter(new AgeFilter());

    proxy.doFilter("張三", 0);
  }
}
=======
username: 張三1  age: 0
正在執(zhí)行：NameFilter
username: 張三1  age: 10
正在執(zhí)行：AgeFilter
過濾器鏈執(zhí)行結(jié)束

在這個執(zhí)行邏輯中，最重要的是【this】，this就是初始化的好的FilterChain實(shí)例，在這個測試實(shí)例中，this就是FilterChainProxy。

執(zhí)行FilterChainProxy的doFilter方法的時候，傳入了初始參數(shù)username和age，進(jìn)入這個方法后，根據(jù)position取出相應(yīng)的Filter，初次進(jìn)入position是0，執(zhí)行Filter的doFilter方法，注意，此時Filter的doFilter方法額外傳入了一個this參數(shù)，這個參數(shù)就是初始化的好的FilterChain實(shí)例，在Filter中的doFilter的方法中最后又會執(zhí)行FilterChain的doFilter方法，相當(dāng)于第二次調(diào)用FilterChain實(shí)例的doFilter方法，此時posotion是1，然后再執(zhí)行Filter的doFilter方法，直到所有的Filter執(zhí)行完，整個執(zhí)行過程結(jié)束。

VirtualFilterChain的doFilter方法的執(zhí)行邏輯和這個測試實(shí)例中的執(zhí)行邏輯基本一致。

這樣就完成了整個過濾器鏈的執(zhí)行。

總結(jié)

以前用Filter的時候就非常疑惑過濾器怎么執(zhí)行的，直到今天才算解決了這個疑惑。

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持億速云。

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詳解spring security filter的工作原理

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