How to include an external jar in a GWT module?

Question

I would like to use the org.apache.commons.validator.GenericValidator class in a view class of my GWT web app. I have read that I have to implicitely tell that I intend to use this external library. I thought adding the next line into my App.gwt.xml would work.

<inherits name='org.apache.commons.validator.GenericValidator'/>

I get the next error:

    Loading inherited module 'org.apache.commons.validator.GenericValidator'
       [ERROR] Unable to find 'org/apache/commons/validator/GenericValidator.gwt.xml' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?
    [ERROR] Line 13: Unexpected exception while processing element 'inherits'
    com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
at com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:239)
    at com.google.gwt.dev.cfg.ModuleDefSchema$BodySchema.__inherits_begin(ModuleDefSchema.java:354)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.util.xml.HandlerMethod.invokeBegin(HandlerMethod.java:223)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.startElement(ReflectiveParser.java:270)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:501)
    at com.sun.org.apache.xerces.internal.parsers.AbstractXMLDocumentParser.emptyElement(AbstractXMLDocumentParser.java:179)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(XMLDocumentFragmentScannerImpl.java:1339)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2747)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:807)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.parse(ReflectiveParser.java:327)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.access$100(ReflectiveParser.java:48)
    at com.google.gwt.dev.util.xml.ReflectiveParser.parse(ReflectiveParser.java:398)
    at com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:257)
    at com.google.gwt.dev.cfg.ModuleDefLoader$1.load(ModuleDefLoader.java:169)
    at com.google.gwt.dev.cfg.ModuleDefLoader.doLoadModule(ModuleDefLoader.java:283)
    at com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(ModuleDefLoader.java:141)
    at com.google.gwt.dev.Compiler.run(Compiler.java:184)
    at com.google.gwt.dev.Compiler$1.run(Compiler.java:152)
    at com.google.gwt.dev.CompileTaskRunner.doRun(CompileTaskRunner.java:87)
    at com.google.gwt.dev.CompileTaskRunner.runWithAppropriateLogger(CompileTaskRunner.java:81)
    at com.google.gwt.dev.Compiler.main(Compiler.java:159)
[ERROR] Failure while parsing XML
com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
    at com.google.gwt.dev.util.xml.DefaultSchema.onHandlerException(DefaultSchema.java:56)
    at com.google.gwt.dev.util.xml.Schema.onHandlerException(Schema.java:66)
    at com.google.gwt.dev.util.xml.Schema.onHandlerException(Schema.java:66)
    at com.google.gwt.dev.util.xml.HandlerMethod.invokeBegin(HandlerMethod.java:233)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.startElement(ReflectiveParser.java:270)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:501)
    at com.sun.org.apache.xerces.internal.parsers.AbstractXMLDocumentParser.emptyElement(AbstractXMLDocumentParser.java:179)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanStartElement(XMLDocumentFragmentScannerImpl.java:1339)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2747)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:648)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:807)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:737)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:107)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1205)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.parse(ReflectiveParser.java:327)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.access$100(ReflectiveParser.java:48)
    at com.google.gwt.dev.util.xml.ReflectiveParser.parse(ReflectiveParser.java:398)
    at com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:257)
    at com.google.gwt.dev.cfg.ModuleDefLoader$1.load(ModuleDefLoader.java:169)
    at com.google.gwt.dev.cfg.ModuleDefLoader.doLoadModule(ModuleDefLoader.java:283)
    at com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(ModuleDefLoader.java:141)
    at com.google.gwt.dev.Compiler.run(Compiler.java:184)
    at com.google.gwt.dev.Compiler$1.run(Compiler.java:152)
    at com.google.gwt.dev.CompileTaskRunner.doRun(CompileTaskRunner.java:87)
    at com.google.gwt.dev.CompileTaskRunner.runWithAppropriateLogger(CompileTaskRunner.java:81)
    at com.google.gwt.dev.Compiler.main(Compiler.java:159)
[ERROR] Unexpected error while processing XML
com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.parse(ReflectiveParser.java:351)
    at com.google.gwt.dev.util.xml.ReflectiveParser$Impl.access$100(ReflectiveParser.java:48)
    at com.google.gwt.dev.util.xml.ReflectiveParser.parse(ReflectiveParser.java:398)
    at com.google.gwt.dev.cfg.ModuleDefLoader.nestedLoad(ModuleDefLoader.java:257)
    at com.google.gwt.dev.cfg.ModuleDefLoader$1.load(ModuleDefLoader.java:169)
    at com.google.gwt.dev.cfg.ModuleDefLoader.doLoadModule(ModuleDefLoader.java:283)
    at com.google.gwt.dev.cfg.ModuleDefLoader.loadFromClassPath(ModuleDefLoader.java:141)
    at com.google.gwt.dev.Compiler.run(Compiler.java:184)
    at com.google.gwt.dev.Compiler$1.run(Compiler.java:152)
    at com.google.gwt.dev.CompileTaskRunner.doRun(CompileTaskRunner.java:87)
    at com.google.gwt.dev.CompileTaskRunner.runWithAppropriateLogger(CompileTaskRunner.java:81)
    at com.google.gwt.dev.Compiler.main(Compiler.java:159)

I have commons.validator-1.3.1.jar in war/WEB-INF/lib

I am using eclipse with Google Plugin.

Anyone knows how it works?

Answer 1

The syntax <inherits name='package.SomeModule'/> is only for special GWT modules, built to be used with GWT, not generics Java libraries (docs). A quick test to see if a jar/library is built to be used with GWT is to see if it includes a module file. If you look at the error you posted the top line reads:

Loading inherited module 'org.apache.commons.validator.GenericValidator'
       [ERROR] Unable to find 'org/apache/commons/validator/GenericValidator.gwt.xml' on your classpath; could be a typo, or maybe you forgot to include a classpath entry for source?

You can see that commons.validator is missing the required module file. You can still use this library on the server side (no restrictions there). For client side, chances are GWT doesn't emulate the required parts of Java - for more information see the docs.