Java教程
tomcat源码研究：tomcat自动重载改变的类
在tomcat6源码中，检查文件是否发生改变的任务由org.apache.catalina.core.StandardContext
类中的backgroundProcess()方法来执行。这个方法周期性地被org.apache.catalina.core.ContainerBase类中一个专门的线程调用，该类中的内部类ContainerBackgroundProcessor实现了Runnable接口。代码如下：
/**
* Private thread class to invoke the backgroundProcess method
* of this container and its children after a fixed delay.
*/
protected class ContainerBackgroundProcessor implements Runnable {
public void run() {
while (!threadDone) {
try {
Thread.sleep(backgroundProcessorDelay * 1000L);
} catch (InterruptedException e) {
;
}
if (!threadDone) {
Container parent = (Container) getMappingObject();
ClassLoader cl =
Thread.currentThread().getContextClassLoader();
if (parent.getLoader() != null) {
cl = parent.getLoader().getClassLoader();
}
processChildren(parent, cl);
}
}
}
protected void processChildren(Container container, ClassLoader cl) {
try {
if (container.getLoader() != null) {
Thread.currentThread().setContextClassLoader
(container.getLoader().getClassLoader());
}
container.backgroundProcess();
} catch (Throwable t) {
log.error("Exception invoking periodic operation: ", t);
} finally {
Thread.currentThread().setContextClassLoader(cl);
}
Container[] children = container.findChildren();
for (int i = 0; i < children.length; i++) {
if (children[i].getBackgroundProcessorDelay() <= 0) {
processChildren(children[i], cl);
}
}
}
}
}
这个线程的run()方法里面有个while循环，该循环有三个作用:
以backgroundProcessorDelay为周期周期性地睡眠；
通过调用WebappLoader类的modified()方法检查加载的类是否发生改变，如果改变，通知和这个servlet容器关联的加载器重新加载。
java.org.apache.catalina.core.StandardWrapper.java
public void backgroundProcess() {
super.backgroundProcess();
if (!started)
return;
if (getServlet() != null && (getServlet() instanceof PeriodicEventListener)) {
((PeriodicEventListener) getServlet()).periodicEvent();
}
}
public void periodicEvent() {
rctxt.checkCompile();
}
java.org.apache.jasper.servlet.JspServlet.java
public void periodicEvent() {
rctxt.checkCompile();
}
java.org.apache.jasper.compiler.JspRuntimeContexxt.java
public void checkCompile() {
if (lastCheck < 0) {
// Checking was disabled
return;
}
long now = System.currentTimeMillis();
if (now > (lastCheck + (options.getCheckInterval() * 1000L))) {
lastCheck = now;
} else {
return;
}
Object [] wrappers = jsps.values().toArray();
for (int i = 0; i < wrappers.length; i++ ) {
JspServletWrapper jsw = (JspServletWrapper)wrappers[i];
JspCompilationContext ctxt = jsw.getJspEngineContext();
// JspServletWrapper also synchronizes on this when
// it detects it has to do a reload
synchronized(jsw) {
try {
ctxt.compile();
} catch (FileNotFoundException ex) {
ctxt.incrementRemoved();
} catch (Throwable t) {
jsw.getServletContext().log("Background compile failed",
t);
}
}
}
java.org.apache.jasper.JspCompilationContext.java
public void compile() throws JasperException, FileNotFoundException {
createCompiler();
if (isPackagedTagFile || 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;
}
}
}
/**
* Create a "Compiler" object based on some init param data. This
* is not done yet. Right now we're just hardcoding the actual
* compilers that are created.
*/
public Compiler createCompiler() throws JasperException {
if (jspCompiler != null ) {
return jspCompiler;
}
jspCompiler = null;
if (options.getCompilerClassName() != null) {
jspCompiler = createCompiler(options.getCompilerClassName());
} else {
if (options.getCompiler() == null) {
jspCompiler = createCompiler("org.apache.jasper.compiler.JDTCompiler");
if (jspCompiler == null) {
jspCompiler = createCompiler("org.apache.jasper.compiler.AntCompiler");
}
} else {
jspCompiler = createCompiler("org.apache.jasper.compiler.AntCompiler");
if (jspCompiler == null) {
jspCompiler = createCompiler("org.apache.jasper.compiler.JDTCompiler");
}
}
}
if (jspCompiler == null) {
throw new IllegalStateException(Localizer.getMessage("jsp.error.compiler"));
}
jspCompiler.init(this, jsw);
return jspCompiler;
}
最后附上编译类的抽象类，大家可以参考研究
java.org.apache.jasper.Compiler.Compiler.java
/**
* Compile the jsp file from the current engine context. As an side- effect,
* tag files that are referenced by this page are also compiled.
*
* @param compileClass
* If true, generate both .java and .class file If false,
* generate only .java file
* @param jspcMode
* true if invoked from JspC, false otherwise
*/
/*
* Copyright 1999,2004-2006 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jasper.compiler;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Iterator;
import java.util.List;
import org.apache.jasper.JasperException;
import org.apache.jasper.JspCompilationContext;
import org.apache.jasper.Options;
import org.apache.jasper.servlet.JspServletWrapper;
/**
* Main JSP compiler class. This class uses Ant for compiling.
*
* @author Anil K. Vijendran
* @author Mandar Raje
* @author Pierre Delisle
* @author Kin-man Chung
* @author Remy Maucherat
* @author Mark Roth
*/
public abstract class Compiler {
protected org.apache.juli.logging.Log log = org.apache.juli.logging.LogFactory
.getLog(Compiler.class);
// ----------------------------------------------------- Instance Variables
protected JspCompilationContext ctxt;
protected ErrorDispatcher errDispatcher;
protected PageInfo pageInfo;
protected JspServletWrapper jsw;
protected TagFileProcessor tfp;
protected Options options;
protected Node.Nodes pageNodes;
// ------------------------------------------------------------ Constructor
public void init(JspCompilationContext ctxt, JspServletWrapper jsw) {
this.jsw = jsw;
this.ctxt = ctxt;
this.options = ctxt.getOptions();
}
// --------------------------------------------------------- Public Methods
/**
* <p>
* Retrieves the parsed nodes of the JSP page, if they are available. May
* return null. Used in development mode for generating detailed error
* messages. http://issues.apache.org/bugzilla/show_bug.cgi?id=37062.
* </p>
*/
public Node.Nodes getPageNodes() {
return this.pageNodes;
}
/**
* Compile the jsp file into equivalent servlet in .java file
*
* @return a smap for the current JSP page, if one is generated, null
* otherwise
*/
protected String[] generateJava() throws Exception {
String[] smapStr = null;
long t1, t2, t3, t4;
t1 = t2 = t3 = t4 = 0;
if (log.isDebugEnabled()) {
t1 = System.currentTimeMillis();
}
// Setup page info area
pageInfo = new PageInfo(new BeanRepository(ctxt.getClassLoader(),
errDispatcher), ctxt.getJspFile());
JspConfig jspConfig = options.getJspConfig();
JspConfig.JspProperty jspProperty = jspConfig.findJspProperty(ctxt
.getJspFile());
/*
* If the current uri is matched by a pattern specified in a
* jsp-property-group in web.xml, initialize pageInfo with those
* properties.
*/
if (jspProperty.isELIgnored() != null) {
pageInfo.setELIgnored(JspUtil.booleanValue(jspProperty
.isELIgnored()));
}
if (jspProperty.isScriptingInvalid() != null) {
pageInfo.setScriptingInvalid(JspUtil.booleanValue(jspProperty
.isScriptingInvalid()));
}
if (jspProperty.getIncludePrelude() != null) {
pageInfo.setIncludePrelude(jspProperty.getIncludePrelude());
}
if (jspProperty.getIncludeCoda() != null) {
pageInfo.setIncludeCoda(jspProperty.getIncludeCoda());
}
if (jspProperty.isDeferedSyntaxAllowedAsLiteral() != null) {
pageInfo.setDeferredSyntaxAllowedAsLiteral(JspUtil.booleanValue(jspProperty
.isDeferedSyntaxAllowedAsLiteral()));
}
if (jspProperty.isTrimDirectiveWhitespaces() != null) {
pageInfo.setTrimDirectiveWhitespaces(JspUtil.booleanValue(jspProperty
.isTrimDirectiveWhitespaces()));
}
ctxt.checkOutputDir();
String javaFileName = ctxt.getServletJavaFileName();
ServletWriter writer = null;
try {
// Setup the ServletWriter
String javaEncoding = ctxt.getOptions().getJavaEncoding();
OutputStreamWriter osw = null;
try {
osw = new OutputStreamWriter(
new FileOutputStream(javaFileName), javaEncoding);
} catch (UnsupportedEncodingException ex) {
errDispatcher.jspError("jsp.error.needAlternateJavaEncoding",
javaEncoding);
}
writer = new ServletWriter(new PrintWriter(osw));
ctxt.setWriter(writer);
// Reset the temporary variable counter for the generator.
JspUtil.resetTemporaryVariableName();
// Parse the file
ParserController parserCtl = new ParserController(ctxt, this);
pageNodes = parserCtl.parse(ctxt.getJspFile());
if (ctxt.isPrototypeMode()) {
// generate prototype .java file for the tag file
Generator.generate(writer, this, pageNodes);
writer.close();
writer = null;
return null;
}
// Validate and process attributes
Validator.validate(this, pageNodes);
if (log.isDebugEnabled()) {
t2 = System.currentTimeMillis();
}
// Collect page info
Collector.collect(this, pageNodes);
// Compile (if necessary) and load the tag files referenced in
// this compilation unit.
tfp = new TagFileProcessor();
tfp.loadTagFiles(this, pageNodes);
if (log.isDebugEnabled()) {
t3 = System.currentTimeMillis();
}
// Determine which custom tag needs to declare which scripting vars
ScriptingVariabler.set(pageNodes, errDispatcher);
// Optimizations by Tag Plugins
TagPluginManager tagPluginManager = options.getTagPluginManager();
tagPluginManager.apply(pageNodes, errDispatcher, pageInfo);
// Optimization: concatenate contiguous template texts.
TextOptimizer.concatenate(this, pageNodes);
// Generate static function mapper codes.
ELFunctionMapper.map(this, pageNodes);
// generate servlet .java file
Generator.generate(writer, this, pageNodes);
writer.close();
writer = null;
// The writer is only used during the compile, dereference
// it in the JspCompilationContext when done to allow it
// to be GC'd and save memory.
ctxt.setWriter(null);
if (log.isDebugEnabled()) {
t4 = System.currentTimeMillis();
log.debug("Generated " + javaFileName + " total=" + (t4 - t1)
+ " generate=" + (t4 - t3) + " validate=" + (t2 - t1));
}
} catch (Exception e) {
if (writer != null) {
try {
writer.close();
writer = null;
} catch (Exception e1) {
// do nothing
}
}
// Remove the generated .java file
new File(javaFileName).delete();
throw e;
} finally {
if (writer != null) {
try {
writer.close();
} catch (Exception e2) {
// do nothing
}
}
}
// JSR45 Support
if (!options.isSmapSuppressed()) {
smapStr = SmapUtil.generateSmap(ctxt, pageNodes);
}
// If any proto type .java and .class files was generated,
// the prototype .java may have been replaced by the current
// compilation (if the tag file is self referencing), but the
// .class file need to be removed, to make sure that javac would
// generate .class again from the new .java file just generated.
tfp.removeProtoTypeFiles(ctxt.getClassFileName());
return smapStr;
}
/**
* Compile the servlet from .java file to .class file
*/
protected abstract void generateClass(String[] smap)
throws FileNotFoundException, JasperException, Exception;
/**
* Compile the jsp file from the current engine context
*/
public void compile() throws FileNotFoundException, JasperException,
Exception {
compile(true);
}
/**
* Compile the jsp file from the current engine context. As an side- effect,
* tag files that are referenced by this page are also compiled.
*
* @param compileClass
* If true, generate both .java and .class file If false,
* generate only .java file
*/
public void compile(boolean compileClass) throws FileNotFoundException,
JasperException, Exception {
compile(compileClass, false);
}
/**
* Compile the jsp file from the current engine context. As an side- effect,
* tag files that are referenced by this page are also compiled.
*
* @param compileClass
* If true, generate both .java and .class file If false,
* generate only .java file
* @param jspcMode
* true if invoked from JspC, false otherwise
*/
public void compile(boolean compileClass, boolean jspcMode)
throws FileNotFoundException, JasperException, Exception {
if (errDispatcher == null) {
this.errDispatcher = new ErrorDispatcher(jspcMode);
}
try {
String[] smap = generateJava();
if (compileClass) {
generateClass(smap);
}
} finally {
if (tfp != null) {
tfp.removeProtoTypeFiles(null);
}
// Make sure these object which are only used during the
// generation and compilation of the JSP page get
// dereferenced so that they can be GC'd and reduce the
// memory footprint.
tfp = null;
errDispatcher = null;
pageInfo = null;
// Only get rid of the pageNodes if in production.
// In development mode, they are used for detailed
// error messages.
// http://issues.apache.org/bugzilla/show_bug.cgi?id=37062
if (!this.options.getDevelopment()) {
pageNodes = null;
}
if (ctxt.getWriter() != null) {
ctxt.getWriter().close();
ctxt.setWriter(null);
}
}
}
/**
* This is a protected method intended to be overridden by subclasses of
* Compiler. This is used by the compile method to do all the compilation.
*/
public boolean isOutDated() {
return isOutDated(true);
}
/**
* Determine if a compilation is necessary by checking the time stamp of the
* JSP page with that of the corresponding .class or .java file. If the page
* has dependencies, the check is also extended to its dependeants, and so
* on. This method can by overidden by a subclasses of Compiler.
*
* @param checkClass
* If true, check against .class file, if false, check against
* .java file.
*/
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();
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 includeUconn = includeUrl.openConnection();
long includeLastModified = includeUconn.getLastModified();
includeUconn.getInputStream().close();
if (includeLastModified > targetLastModified) {
return true;
}
} catch (Exception e) {
return true;
}
}
return false;
}
/**
* Gets the error dispatcher.
*/
public ErrorDispatcher getErrorDispatcher() {
return errDispatcher;
}
/**
* Gets the info about the page under compilation
*/
public PageInfo getPageInfo() {
return pageInfo;
}
public JspCompilationContext getCompilationContext() {
return ctxt;
}
/**
* Remove generated files
*/
public void removeGeneratedFiles() {
try {
String classFileName = ctxt.getClassFileName();
if (classFileName != null) {
File classFile = new File(classFileName);
if (log.isDebugEnabled())
log.debug("Deleting " + classFile);
classFile.delete();
}
} catch (Exception e) {
// Remove as much as possible, ignore possible exceptions
}
try {
String javaFileName = ctxt.getServletJavaFileName();
if (javaFileName != null) {
File javaFile = new File(javaFileName);
if (log.isDebugEnabled())
log.debug("Deleting " + javaFile);
javaFile.delete();
}
} catch (Exception e) {
// Remove as much as possible, ignore possible exceptions
}
}
public void removeGeneratedClassFiles() {
try {
String classFileName = ctxt.getClassFileName();
if (classFileName != null) {
File classFile = new File(classFileName);
if (log.isDebugEnabled())
log.debug("Deleting " + classFile);
classFile.delete();
}
} catch (Exception e) {
// Remove as much as possible, ignore possible exceptions
}
}
}
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