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Tomcat 6 --- 使用Jasper引擎解析JSP

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

Tomcat 6 --- 使用Jasper引擎解析JSP

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。

Tomcat 6 --- 使用Jasper引擎解析JSP

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());    }   }