tomcat之是否编译JSP的条件

我们在开发的过程中，修改JSP的内容后，不启动容器的情况下，可以进行应用，这是为什么呢？ 容器到底做了什么呢？ 它怎么知道我们的JSP有变化呢？ 哈哈，接下来我们就来揭开TOMCAT的这层面纱：1.我们在访问JSP面的的时候执行的流程为：  容器启动后，会有一个无限循环的等待来接由客户端的请求，这个是由JIoEndpoint.Acceptor线程来完成的，代码如下：protected class Acceptor implements Runnable {        /**         * The background thread that listens for incoming TCP/IP connections and         * hands them off to an appropriate processor.         */        public void run() {            // Loop until we receive a shutdown command            while (running) {                // Loop if endpoint is paused                while (paused) {                    try {                        Thread.sleep(1000);                    } catch (InterruptedException e) {                        // Ignore                    }                }                // Accept the next incoming connection from the server socket                try {                    Socket socket = serverSocketFactory.acceptSocket(serverSocket);                    serverSocketFactory.initSocket(socket);                    // Hand this socket off to an appropriate processor                    if (!processSocket(socket)) {                        // Close socket right away                        try {                            socket.close();                        } catch (IOException e) {                            // Ignore                        }                    }                }catch ( IOException x ) {                    if ( running ) log.error(sm.getString("endpoint.accept.fail"), x);                } catch (Throwable t) {                    log.error(sm.getString("endpoint.accept.fail"), t);                }                // The processor will recycle itself when it finishes            }        }    }2.当容器收到一个请求后，CoyoteAdapter类的service方法来处理 ，然后通过责任链模式调用到StandardWrapperValve.java类invoke方法中调用ApplicationFilterChain类的doFilter  接着来到HttpServlet的Service方法中 调用JspServlet.java类的service方法中，serviceJspFile 。。。JspServletWrapper.java类的service方法中， if (options.getDevelopment() || firstTime ) {                synchronized (this) {                    firstTime = false;                    // The following sets reload to true, if necessary                    ctxt.compile();                }            } else {                if (compileException != null) {                    // Throw cached compilation exception                    throw compileException;                }            }最后来到，JspCompilationContext.java类的compile方法中，重点来了，public void compile() throws JasperException, FileNotFoundException {        createCompiler();        [b]if (jspCompiler.isOutDated()) {[/b]            try {                jspCompiler.removeGeneratedFiles();                jspLoader = null;                jspCompiler.compile();                jsw.setReload(true);                jsw.setCompilationException(null);            } catch (JasperException ex) {                // Cache compilation exception                jsw.setCompilationException(ex);                throw ex;            } catch (Exception ex) {                JasperException je = new JasperException(                            Localizer.getMessage("jsp.error.unable.compile"),                            ex);                // Cache compilation exception                jsw.setCompilationException(je);                throw je;            }        }    }以上加粗的地方来判断是否进行重新编译JSP页面，public boolean isOutDated(boolean checkClass) {        String jsp = ctxt.getJspFile();        if (jsw != null                && (ctxt.getOptions().getModificationTestInterval() > 0)) {            if (jsw.getLastModificationTest()                    + (ctxt.getOptions().getModificationTestInterval() * 1000) > System                    .currentTimeMillis()) {                return false;            } else {                jsw.setLastModificationTest(System.currentTimeMillis());            }        }        long jspRealLastModified = 0;        try {            URL jspUrl = ctxt.getResource(jsp);            if (jspUrl == null) {                ctxt.incrementRemoved();                return false;            }            URLConnection uc = jspUrl.openConnection();            if (uc instanceof JarURLConnection) {                jspRealLastModified =                    ((JarURLConnection) uc).getJarEntry().getTime();            } else {                jspRealLastModified = uc.getLastModified();            }            uc.getInputStream().close();        } catch (Exception e) {            return true;        }        long targetLastModified = 0;        File targetFile;        if (checkClass) {            targetFile = new File(ctxt.getClassFileName());        } else {            targetFile = new File(ctxt.getServletJavaFileName());        }        if (!targetFile.exists()) {            return true;        }        targetLastModified = targetFile.lastModified();        if (checkClass && jsw != null) {            jsw.setServletClassLastModifiedTime(targetLastModified);        }        if (targetLastModified < jspRealLastModified) {            if (log.isDebugEnabled()) {                log.debug("Compiler: outdated: " + targetFile + " "                        + targetLastModified);            }            return true;        }        // determine if source dependent files (e.g. includes using include        // directives) have been changed.        if (jsw == null) {            return false;        }        List depends = jsw.getDependants();        if (depends == null) {            return false;        }        Iterator it = depends.iterator();        while (it.hasNext()) {            String include = (String) it.next();            try {                URL includeUrl = ctxt.getResource(include);                if (includeUrl == null) {                    return true;                }                URLConnection iuc = includeUrl.openConnection();                long includeLastModified = 0;                if (iuc instanceof JarURLConnection) {                    includeLastModified =                        ((JarURLConnection) iuc).getJarEntry().getTime();                } else {                    includeLastModified = iuc.getLastModified();                }                iuc.getInputStream().close();                if (includeLastModified > targetLastModified) {                    return true;                }            } catch (Exception e) {                return true;            }        }        return false;    }