Tomcat 6 --- 使用Jasper引擎解析JSP

2015-07-07 23:15:38   来源:cnblogs   评论: 点击:

熟悉JAVA web开发的朋友都知道JSP会被转换成java文件(预编译),然后编译成class使用,即按照JSP-->java-->class的过程进行编译。由于JVM只认识class文件,它不知道什么是JSP,因此在tomcat中
熟悉JAVA web开发的朋友都知道JSP会被转换成java文件(预编译),然后编译成class使用,即按照JSP-->java-->class的过程进行编译。

由于JVM只认识class文件,它不知道什么是JSP,因此在tomcat中 如何把JSP解析成java文件 就是本文所要描述的问题。

其他翻译内容参考:Tomcat官方文档翻译

如有错误,请予指正。

什么是Jasper

Jasper是tomcat中使用的JSP引擎,在Tomcat 6中使用的是Jasper 2,相对于原来的版本作了不少的改进,比如: JSP的标签缓冲池、后台编译、页面改变时自动重新编译、Eclipse中JDT编译 等等。

那么Jasper到底是做什么的呢?

简单的说,就是把JVM不认识的JSP文件解析成java文件,然后编译成class文件提供使用。目前有很多的JSP解析引擎,Tomcat中使用的是Jasper。

在Tomcat中可以通过配置 CATALINA_HOME/conf/web.xml  中的内容,配置Jasper的选项(web.xml中的内容很长,截取其中的一部分):

<!-- The JSP page compiler and execution servlet, which is the mechanism  -->
<!-- used by Tomcat to support JSP pages.  Traditionally, this servlet	-->
<!-- is mapped to the URL pattern "*.jsp".  This servlet supports the	 -->
<!-- following initialization parameters (default values are in square	-->
<!-- brackets):														   -->
<!--																	  -->
<!--   checkInterval	   If development is false and checkInterval is   -->
<!--					   greater than zero, background compilations are -->
<!--					   enabled. checkInterval is the time in seconds  -->
<!--					   between checks to see if a JSP page (and its   -->
<!--					   dependent files) needs to  be recompiled. [0]  -->
<!--																	  -->
<!--   classdebuginfo	  Should the class file be compiled with		 -->
<!--					   debugging information?  [true]				 -->
<!--																	  -->
<!--   classpath		   What class path should I use while compiling   -->
<!--					   generated servlets?  [Created dynamically	  -->
<!--					   based on the current web application]		  -->
<!--																	  -->
<!--   compiler			Which compiler Ant should use to compile JSP   -->
<!--					   pages.  See the jasper documentation for more  -->
<!--					   information.								   -->
<!--																	  -->
<!--   compilerSourceVM	Compiler source VM. [1.5]					  -->
<!--																	  -->
<!--   compilerTargetVM	Compiler target VM. [1.5]					  -->  
<!--																	  -->
<!--   development		 Is Jasper used in development mode? If true,   -->
<!--					   the frequency at which JSPs are checked for	-->
<!--					   modification may be specified via the		  -->
<!--					   modificationTestInterval parameter. [true]	 -->
<!--																	  -->
<!--   displaySourceFragment											  -->
<!--					   Should a source fragment be included in		-->
<!--					   exception messages? [true]					 -->
<!--																	  -->
<!--   dumpSmap			Should the SMAP info for JSR45 debugging be	-->
<!--					   dumped to a file? [false]					  -->
<!--					   False if suppressSmap is true				  -->
<!--																	  -->
<!--   enablePooling	   Determines whether tag handler pooling is	  -->
<!--					   enabled. This is a compilation option. It will -->
<!--					   not alter the behaviour of JSPs that have	  -->
<!--					   already been compiled. [true]				  -->
<!--																	  -->
<!--   engineOptionsClass  Allows specifying the Options class used to	-->
<!--					   configure Jasper. If not present, the default  -->
<!--					   EmbeddedServletOptions will be used.		   -->
<!--																	  -->
<!--   errorOnUseBeanInvalidClassAttribute								-->
<!--					   Should Jasper issue an error when the value of -->
<!--					   the class attribute in an useBean action is	-->
<!--					   not a valid bean class?  [true]				-->
<!--																	  -->
<!--   fork				Tell Ant to fork compiles of JSP pages so that -->
<!--					   a separate JVM is used for JSP page compiles   -->
<!--					   from the one Tomcat is running in. [true]	  -->
<!--																	  -->
<!--   genStringAsCharArray											   -->
<!--					   Should text strings be generated as char	   -->
<!--					   arrays, to improve performance in some cases?  -->
<!--					   [false]										-->
<!--																	  -->
<!--   ieClassId		   The class-id value to be sent to Internet	  -->
<!--					   Explorer when using <jsp:plugin> tags.		 -->
<!--					   [clsid:8AD9C840-044E-11D1-B3E9-00805F499D93]   -->
<!--																	  -->
<!--   javaEncoding		Java file encoding to use for generating java  -->
<!--					   source files. [UTF8]						   -->
<!--																	  -->
<!--   keepgenerated	   Should we keep the generated Java source code  -->
<!--					   for each page instead of deleting it? [true]   -->
<!--																	  -->
<!--   mappedfile		  Should we generate static content with one	 -->
<!--					   print statement per input line, to ease		-->
<!--					   debugging?  [true]							 -->
<!--																	  -->
<!--   modificationTestInterval										   -->
<!--					   Causes a JSP (and its dependent files) to not  -->
<!--					   be checked for modification during the		 -->
<!--					   specified time interval (in seconds) from the  -->
<!--					   last time the JSP was checked for			  -->
<!--					   modification. A value of 0 will cause the JSP  -->
<!--					   to be checked on every access.				 -->
<!--					   Used in development mode only. [4]			 -->
<!--																	  -->
<!--   recompileOnFail	 If a JSP compilation fails should the		  -->
<!--					   modificationTestInterval be ignored and the	-->
<!--					   next access trigger a re-compilation attempt?  -->
<!--					   Used in development mode only and is disabled  -->
<!--					   by default as compilation may be expensive and -->
<!--					   could lead to excessive resource usage.		-->
<!--					   [false]										-->
<!--																	  -->
<!--   scratchdir		  What scratch directory should we use when	  -->
<!--					   compiling JSP pages?  [default work directory  -->
<!--					   for the current web application]			   -->
<!--																	  -->
<!--   suppressSmap		Should the generation of SMAP info for JSR45   -->
<!--					   debugging be suppressed?  [false]			  -->
<!--																	  -->
<!--   trimSpaces		  Should white spaces in template text between   -->
<!--					   actions or directives be trimmed?  [false]	 -->
<!--																	  -->
<!--   xpoweredBy		  Determines whether X-Powered-By response	   -->
<!--					   header is added by generated servlet  [false]  -->
<!--																	  -->
<!-- If you wish to use Jikes to compile JSP pages:					   -->
<!--   Please see the "Using Jikes" section of the Jasper-HowTo		   -->
<!--   page in the Tomcat documentation.								  -->
  <servlet>
    <servlet-name>jsp</servlet-name>
    <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
    <init-param>
      <param-name>fork</param-name>
      <param-value>false</param-value>
    </init-param>
    <init-param>
      <param-name>xpoweredBy</param-name>
      <param-value>false</param-value>
    </init-param>
    <load-on-startup>3</load-on-startup>
  </servlet>

具体的参数,上面都有解释,这里就不多赘述了。

都是些调节JSP编译的参数,比如多长时间检测一次,debug的调试信息相关配置,编译信息等等。

如何利用Japser.Jspc自定义预编译JSP

1 jasper相关jar包

在tomcat6中提供了几个jasper的jar包,相对于之前版本,去掉了jasper-compiler.jar以及jasper-runtime.jar,合并为jasper.jar

另外如果开发者自己想要编译JSP,还需要使用ant以及tomcat-juli.jar。

2 ant相关jar包

其中ant相关的jar包可以去官网下载ant.zip,然后解压提取其中lib内的jar包。

3 tomcat-juli相关jar包

tomcat-juli.jar位于CATALINA_HOME/bin/目录下。

在Eclipse的构建路径下添加上述相关的jar包即可,然后创建测试类:

添加JAR包步骤:右键工程-->Properties-->Java Build Path-->Libraries-->Add External JARs-->选择添加的JAR包-->OK

package com.test;
import org.apache.jasper.JspC;
public class testCompiler{
  public String jspcTest(){  
    String error="";  
    try {  
      JspC jspc = new JspC();  
      //第一种方式
      String[] arg0 = {"-uriroot", "F:/apache-tomcat-6.0.43/webapps/ROOT", "-d", "F:/test", 
          "index.jsp" }; 
      jspc.setArgs(arg0); 
      //第二种方式
      /*jspc.setUriroot("F:/apache-tomcat-6.0.43/webapps/ROOT");//web应用的root目录  
      jspc.setOutputDir("F:/test");//.java文件和.class文件的输出目录  
      jspc.setJspFiles("index.jsp");//要编译的jsp  */
      jspc.setCompile(true);//是否编译 false或不指定的话只生成.java文件  
      jspc.execute(); 
    }catch(Exception e){
      error=e.toString();
    }
    return error;  
  }
  public static void main(String args[]){  
    testCompiler t=new testCompiler();  
    System.out.println(t.jspcTest());  
  }  
}  

可以使用两种方式进行自定义的JSP编译。

测试后,可以在 F:/test  目录下发现编译出的index.jsp的java文件以及class文件。

参考

【1】Jasper2 JSP引擎: http://tomcat.apache.org/tomcat-6.0-doc/jasper-howto.html

【2】解读JSP解析过程: http://www.cnblogs.com/zollty/p/3309310.html

【3】使用Jspc编译JSP文件: http://kjah.iteye.com/blog/625588

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