tomcat之是否编译JSP的条件

284354749

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();
if (jspCompiler.isOutDated()) {
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;
}