什么是Jasper

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。