Tomcat

Tomcat请求处理分析(二) - 容器组件处理过程

2018-09-13  本文已影响2人  buzzerrookie

本文接着上一篇文章分析Tomcat是如何处理请求的，主要涉及到各个容器组件如Engine、Host和Context的处理过程。

Engine处理请求

StandardEngineValve的invoke方法代码如下，最后一句委托给Host去处理：

@Override
public final void invoke(Request request, Response response)
    throws IOException, ServletException {
    // Select the Host to be used for this Request
    Host host = request.getHost();
    if (host == null) {
        response.sendError
            (HttpServletResponse.SC_BAD_REQUEST,
                sm.getString("standardEngine.noHost",
                            request.getServerName()));
        return;
    }
    if (request.isAsyncSupported()) {
        request.setAsyncSupported(host.getPipeline().isAsyncSupported());
    }
    // Ask this Host to process this request
    host.getPipeline().getFirst().invoke(request, response);
}

Host处理请求

接着Host会去处理请求，在Tomcat启动分析(七) - Container及相关组件中曾提到StandardHost的构造函数为自己的Pipeline添加了基本阀StandardHostValve，StandardPipeline调用getFirst得到第一个阀去处理请求，由于基本阀是最后一个，所以最后会由基本阀去处理请求。StandardHostValve的invoke方法代码如下：

@Override
public final void invoke(Request request, Response response)
    throws IOException, ServletException {
    // Select the Context to be used for this Request
    Context context = request.getContext();
    if (context == null) {
        response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
                sm.getString("standardHost.noContext"));
        return;
    }

    if (request.isAsyncSupported()) {
        request.setAsyncSupported(context.getPipeline().isAsyncSupported());
    }
    boolean asyncAtStart = request.isAsync();
    boolean asyncDispatching = request.isAsyncDispatching();
    try {
        context.bind(Globals.IS_SECURITY_ENABLED, MY_CLASSLOADER);
        // 省略一些代码
        try {
            if (!asyncAtStart || asyncDispatching) {
                context.getPipeline().getFirst().invoke(request, response);
            } else {
                // Make sure this request/response is here because an error
                // report is required.
                if (!response.isErrorReportRequired()) {
                    throw new IllegalStateException(sm.getString("standardHost.asyncStateError"));
                }
            }
        } catch (Throwable t) {
            // 省略一些代码
        }

        // 省略一些代码
    } finally {
        // 省略一些代码
    }
}

Context处理请求

接着Context会去处理请求，同理，StandardContextValve的invoke方法会被调用：

@Override
public final void invoke(Request request, Response response)
    throws IOException, ServletException {
    // Disallow any direct access to resources under WEB-INF or META-INF
    MessageBytes requestPathMB = request.getRequestPathMB();
    if ((requestPathMB.startsWithIgnoreCase("/META-INF/", 0))
            || (requestPathMB.equalsIgnoreCase("/META-INF"))
            || (requestPathMB.startsWithIgnoreCase("/WEB-INF/", 0))
            || (requestPathMB.equalsIgnoreCase("/WEB-INF"))) {
        response.sendError(HttpServletResponse.SC_NOT_FOUND);
        return;
    }

    // Select the Wrapper to be used for this Request
    Wrapper wrapper = request.getWrapper();
    if (wrapper == null || wrapper.isUnavailable()) {
        response.sendError(HttpServletResponse.SC_NOT_FOUND);
        return;
    }

    // Acknowledge the request
    try {
        response.sendAcknowledgement();
    } catch (IOException ioe) {
        container.getLogger().error(sm.getString(
                "standardContextValve.acknowledgeException"), ioe);
        request.setAttribute(RequestDispatcher.ERROR_EXCEPTION, ioe);
        response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        return;
    }

    if (request.isAsyncSupported()) {
        request.setAsyncSupported(wrapper.getPipeline().isAsyncSupported());
    }
    wrapper.getPipeline().getFirst().invoke(request, response);
}

Wrapper处理请求

接着Wrapper会去处理请求，同理，StandardWrapperValve的invoke方法会被调用：

@Override
public final void invoke(Request request, Response response)
    throws IOException, ServletException {
    // 省略一些代码
    // Create the filter chain for this request
    ApplicationFilterChain filterChain =
            ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);

    // Call the filter chain for this request
    // NOTE: This also calls the servlet's service() method
    try {
        if ((servlet != null) && (filterChain != null)) {
            // Swallow output if needed
            if (context.getSwallowOutput()) {
                try {
                    SystemLogHandler.startCapture();
                    if (request.isAsyncDispatching()) {
                        request.getAsyncContextInternal().doInternalDispatch();
                    } else {
                        filterChain.doFilter(request.getRequest(),
                                response.getResponse());
                    }
                } finally {
                    String log = SystemLogHandler.stopCapture();
                    if (log != null && log.length() > 0) {
                        context.getLogger().info(log);
                    }
                }
            } else {
                if (request.isAsyncDispatching()) {
                    request.getAsyncContextInternal().doInternalDispatch();
                } else {
                    filterChain.doFilter
                        (request.getRequest(), response.getResponse());
                }
            }

        }
    } catch (ClientAbortException e) {
        // 省略一些代码
    }

    // 省略一些代码
}

ApplicationFilterChain过滤器链

ApplicationFilterChain类的doFilter函数代码如下,它会将处理委托给internalDoFilter函数。

@Override
public void doFilter(ServletRequest request, ServletResponse response)
    throws IOException, ServletException {

    if( Globals.IS_SECURITY_ENABLED ) {
        final ServletRequest req = request;
        final ServletResponse res = response;
        try {
            java.security.AccessController.doPrivileged(
                new java.security.PrivilegedExceptionAction<Void>() {
                    @Override
                    public Void run()
                        throws ServletException, IOException {
                        internalDoFilter(req,res);
                        return null;
                    }
                }
            );
        } catch( PrivilegedActionException pe) {
            Exception e = pe.getException();
            if (e instanceof ServletException)
                throw (ServletException) e;
            else if (e instanceof IOException)
                throw (IOException) e;
            else if (e instanceof RuntimeException)
                throw (RuntimeException) e;
            else
                throw new ServletException(e.getMessage(), e);
        }
    } else {
        internalDoFilter(request,response);
    }
}

ApplicationFilterChain类的internalDoFilter函数代码如下：

private void internalDoFilter(ServletRequest request,
                                ServletResponse response)
    throws IOException, ServletException {
    // Call the next filter if there is one
    if (pos < n) {
        ApplicationFilterConfig filterConfig = filters[pos++];
        try {
            Filter filter = filterConfig.getFilter();

            if (request.isAsyncSupported() && "false".equalsIgnoreCase(
                    filterConfig.getFilterDef().getAsyncSupported())) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
            }
            if( Globals.IS_SECURITY_ENABLED ) {
                final ServletRequest req = request;
                final ServletResponse res = response;
                Principal principal =
                    ((HttpServletRequest) req).getUserPrincipal();

                Object[] args = new Object[]{req, res, this};
                SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
            } else {
                filter.doFilter(request, response, this);
            }
        } catch (IOException | ServletException | RuntimeException e) {
            throw e;
        } catch (Throwable e) {
            e = ExceptionUtils.unwrapInvocationTargetException(e);
            ExceptionUtils.handleThrowable(e);
            throw new ServletException(sm.getString("filterChain.filter"), e);
        }
        return;
    }

    // We fell off the end of the chain -- call the servlet instance
    try {
        if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
            lastServicedRequest.set(request);
            lastServicedResponse.set(response);
        }

        if (request.isAsyncSupported() && !servletSupportsAsync) {
            request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
                    Boolean.FALSE);
        }
        // Use potentially wrapped request from this point
        if ((request instanceof HttpServletRequest) &&
                (response instanceof HttpServletResponse) &&
                Globals.IS_SECURITY_ENABLED ) {
            final ServletRequest req = request;
            final ServletResponse res = response;
            Principal principal =
                ((HttpServletRequest) req).getUserPrincipal();
            Object[] args = new Object[]{req, res};
            SecurityUtil.doAsPrivilege("service",
                                        servlet,
                                        classTypeUsedInService,
                                        args,
                                        principal);
        } else {
            servlet.service(request, response);
        }
    } catch (IOException | ServletException | RuntimeException e) {
        throw e;
    } catch (Throwable e) {
        e = ExceptionUtils.unwrapInvocationTargetException(e);
        ExceptionUtils.handleThrowable(e);
        throw new ServletException(sm.getString("filterChain.servlet"), e);
    } finally {
        if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
            lastServicedRequest.set(null);
            lastServicedResponse.set(null);
        }
    }
}
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