How to precompile jsp in a spring boot application? - spring

Question

I'm using Spring boot and we were using Spring with Tomcat before that.
When we used Spring and Tomcat two years ago, we used a maven plugin to precompile the jsp.
It was really useful to avoid this compilation to be made for every first visits after a deployement.
However all maven plugin that we know dumps a web.xml file that list all jsp and associated generated servlets.
With Spring boot, it don't use web.xml anymore, so this file is ignored.
We still have the compilation and that's a security belt but there is a penalty for every first visit on each page.
Does anybody know if it's possible to precompile jsp in a Spring boot application ?

Answer 1

I got precompiling to work either at server start time (don't have to use JspC, so simpler build file) and at build time (much quicker server start time). I register the resulting servlets dynamically, so you don't have to manually change any files if you add/remove JSPs.
At server start time
Use ServletRegistration.Dynamic to register a JSP_SERVLET_CLASS Servlet for each JSP.
Use the initParameter jspFile to set the JSP filename (ref)
e.g. for SpringBoot in a ServletContextInitializer (ref):
#Bean
public ServletContextInitializer preCompileJspsAtStartup() {
return servletContext -> {
getDeepResourcePaths(servletContext, "/WEB-INF/jsp/").forEach(jspPath -> {
log.info("Registering JSP: {}", jspPath);
ServletRegistration.Dynamic reg = servletContext.addServlet(jspPath, Constants.JSP_SERVLET_CLASS);
reg.setInitParameter("jspFile", jspPath);
reg.setLoadOnStartup(99);
reg.addMapping(jspPath);
});
};
}
private static Stream<String> getDeepResourcePaths(ServletContext servletContext, String path) {
return (path.endsWith("/")) ? servletContext.getResourcePaths(path).stream().flatMap(p -> getDeepResourcePaths(servletContext, p))
: Stream.of(path);
}
At build time
Generate Java source files for each JSP and a web.xml with their servlet mappings using JspC (ref).
Then register these with the ServletContext (by parsing the web.xml with Tomcat's WebXmlParser, e.g. for SpringBoot:
#Value("classpath:precompiled-jsp-web.xml")
private Resource precompiledJspWebXml;
#Bean
public ServletContextInitializer registerPreCompiledJsps() {
return servletContext -> {
// Use Tomcat's web.xml parser (assume complete XML file and validate).
WebXmlParser parser = new WebXmlParser(false, true, true);
try (InputStream is = precompiledJspWebXml.getInputStream()) {
WebXml webXml = new WebXml();
boolean success = parser.parseWebXml(new InputSource(is), webXml, false);
if (!success) {
throw new RuntimeException("Error parsing Web XML " + precompiledJspWebXml);
}
for (ServletDef def : webXml.getServlets().values()) {
log.info("Registering precompiled JSP: {} = {} -> {}", def.getServletName(), def.getServletClass());
ServletRegistration.Dynamic reg = servletContext.addServlet(def.getServletName(), def.getServletClass());
reg.setLoadOnStartup(99);
}
for (Map.Entry<String, String> mapping : webXml.getServletMappings().entrySet()) {
log.info("Mapping servlet: {} -> {}", mapping.getValue(), mapping.getKey());
servletContext.getServletRegistration(mapping.getValue()).addMapping(mapping.getKey());
}
} catch (IOException e) {
throw new RuntimeException("Error registering precompiled JSPs", e);
}
};
}
Example Maven config to generate and compile the JSP classes, and generate the precompiled-jsp-web.xml:
<!-- Needed to get the jasper Ant task to work (putting it in the plugin's dependencies didn't work) -->
<dependency>
<groupId>org.apache.tomcat</groupId>
<artifactId>tomcat-catalina-ant</artifactId>
<version>8.0.32</version>
<scope>provided</scope>
</dependency>
<!-- ... -->
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.8</version>
<executions>
<execution>
<id>precompile-jsp-generate-java</id>
<!-- Can't be generate-sources because we need the compiled Henry taglib classes already! -->
<phase>compile</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<echo message="Precompiling JSPs"/>
<property name="compile_classpath" refid="maven.compile.classpath"/>
<property name="target_dir" value="${project.basedir}/generated-sources/jspc" />
<path id="jspc_classpath">
<path path="${compile_classpath}"/>
</path>
<typedef resource="org/apache/catalina/ant/catalina.tasks" classpathref="jspc_classpath"/>
<mkdir dir="${target_dir}/java"/>
<mkdir dir="${target_dir}/resources"/>
<jasper
validateXml="false"
uriroot="${project.basedir}/src/main/webapp"
compilertargetvm="1.8"
compilersourcevm="1.8"
failonerror="true"
javaencoding="UTF-8"
webXml="${target_dir}/resources/precompiled-jsp-web.xml"
outputDir="${target_dir}/java/" >
</jasper>
<!-- Can't use Maven to compile the JSP classes because it has already compiled the app's classes
(needed to do that becuase JspC needs compiled app classes) -->
<javac srcdir="${target_dir}/java" destdir="${project.build.outputDirectory}" classpathref="jspc_classpath" fork="true"/>
<!-- Have to copy the web.xml because process-resources phase has already finished (before compile) -->
<copy todir="${project.build.outputDirectory}">
<fileset dir="${target_dir}/resources"/>
</copy>
</tasks>
</configuration>
</execution>
</executions>
</plugin>
<!-- Not strictly necessary, because Ant does the compilation, but at least attempts to keep it in sync with Maven -->
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<executions>
<execution>
<id>add-precompiled-jsp-java-sources</id>
<phase>generate-sources</phase>
<goals><goal>add-source</goal></goals>
<configuration>
<sources>
<source>${project.basedir}/generated-sources/jspc/java</source>
</sources>
</configuration>
</execution>
<execution>
<id>add-precompiled-jsp-resources</id>
<phase>generate-resources</phase>
<goals><goal>add-resource</goal></goals>
<configuration>
<resources>
<resource>
<directory>${project.basedir}/generated-sources/jspc/resources</directory>
</resource>
</resources>
</configuration>
</execution>
</executions>
</plugin>

Answer 2

Based on the excellent answer of paulcm I came up with my own solution as the above solution didn't work for me and I couldn't track down the error. Maybe the answer above is outdated for tomcat9. Or it had some problem with multi-module setup. However: All credits belong to paulcm
This is only the compile time solution.
Add these two plugins to your pom.xml
<plugin>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-jspc-maven-plugin</artifactId>
<version>9.4.15.v20190215</version>
<executions>
<execution>
<id>jspc</id>
<goals>
<goal>jspc</goal>
</goals>
<configuration>
<mergeFragment>true</mergeFragment>
<sourceVersion>1.8</sourceVersion>
<targetVersion>1.8</targetVersion>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<webXml>${project.basedir}/target/web.xml</webXml>
</configuration>
</plugin>
Add an empty web.xml file
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0"
metadata-complete="true">
<session-config>
<cookie-config>
</cookie-config>
</session-config>
</web-app>
Add a Registry
import org.apache.tomcat.util.descriptor.web.ServletDef;
import org.apache.tomcat.util.descriptor.web.WebXml;
import org.apache.tomcat.util.descriptor.web.WebXmlParser;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.xml.sax.InputSource;
import javax.servlet.ServletRegistration;
import java.io.InputStream;
import java.util.Map;
#Configuration
public class PreCompileJspRegistry {
private Logger logger = LoggerFactory.getLogger(this.getClass());
#Bean
public ServletContextInitializer registerPreCompiledJsps() {
return servletContext -> {
InputStream inputStream = servletContext.getResourceAsStream("/WEB-INF/web.xml");
if (inputStream == null) {
logger.info("Could not read web.xml");
return;
}
try {
WebXmlParser parser = new WebXmlParser(false, false, true);
WebXml webXml = new WebXml();
boolean success = parser.parseWebXml(new InputSource(inputStream), webXml, false);
if (!success) {
logger.error("Error registering precompiled JSPs");
}
for (ServletDef def : webXml.getServlets().values()) {
logger.info("Registering precompiled JSP: {} = {} -> {}", def.getServletName(), def.getServletClass());
ServletRegistration.Dynamic reg = servletContext.addServlet(def.getServletName(), def.getServletClass());
reg.setLoadOnStartup(99);
}
for (Map.Entry<String, String> mapping : webXml.getServletMappings().entrySet()) {
logger.info("Mapping servlet: {} -> {}", mapping.getValue(), mapping.getKey());
servletContext.getServletRegistration(mapping.getValue()).addMapping(mapping.getKey());
}
} catch (Exception e) {
logger.error("Error registering precompiled JSPs", e);
}
};
}
}

Answer 3

A comment for "At server start time" outlined above: the servlet you create will by default be in development mode if the application is packaged in an executable jar, so you if you use it in production mode, you should also set development = false ++ to prevent the jsps from being compiled again:
reg.setInitParameter("genStringAsCharArray", "true");
reg.setInitParameter("trimSpaces", "true");
reg.setInitParameter("development", "false");