Use webapp class path using JavaCompiler in Tomcat in Eclipse with Maven

Question

I have a “Webapp Example” that references the “Example Library” using Maven. I am running Tomcat 7 inside Eclipse 4.3RC3 with the m2e plugin. When I run the Webapp example on Tomcat inside Eclipse, I confirmed that example-library.jar is likely to be deployed to the Tomcat instance folder WEB-INF/lib .

Example Webapp has code that compiles certain classes on the fly using JavaCompiler.CompilationTask . These dynamically generated classes map classes in example-library.jar . Unfortunately, the compilation task fails because the reference classes cannot be found.

I understand that I can set the JavaCompiler classpath , but System.getProperty("java.class.path") returns me the path of the Tomcat class, not the path of the webapp path:

 C:\bin\tomcat\bin\bootstrap.jar;C:\bin\tomcat\bin\tomcat-juli.jar;C:\bin\jdk6\lib\tools.jar 

Others said that I need to get the real WEB-INF/lib path from the servlet context, but the class generation code knows nothing about the context servlet --- it is written as an agnostic about whether it is used on the client or on the server.

In another question , one answer indicated that I can list the URLs of the class loader, and, of course, I provide this with banks in WEB-INF/lib , but when I provide this as the -classpath option for compiler.getTask() , the task still fails because it cannot find the reference classes.

How can I just provide the class path of the current executable code to the JavaCompiler instance so that it finds classes from libraries in WEB-INF/lib ? (A similar question was raised, but he never answered regarding jar links in ear files using JavaCompiler .)

Example. In an attempt to get things to work at all costs, I even tried hardcoded the classpath. For example, I have foobar.lib in my webapp lib directory, so I used the following code, modified from the answers above:

 List<String> options = new ArrayList<String>(); options.add("-classpath"); options.add("C:\\work\\.metadata\\.plugins\\org.eclipse.wst.server.core\\tmp0\\wtpwebapps\\FooBar\\WEB-INF\\lib\\foobar.jar"); JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, diagnostics, options, null, compilationUnits); boolean success = task.call(); 

At the end, success is false , and my diaognostics indicates package com.example.foo.bar does not exist... although this package is in foobar.jar .

Answer 1

Place example-library.jar somewhere on your file system and pass that place to the code that runs JavaCompiler (option -classpath). If you use a deployed WAR file for deployment, you can, of course, point it to a physical location in the WEB-INF / lib folder. The fact is that for this you need only one custom parameter in your webapp, which can be a properties file, -D system property, a database row, or something else.

Sample code (tested on Tomcat 7 and OpenJDK 1.7 on Fedora 18 x64):

 private File compile(File javaFile, String classpath) throws IOException { JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null); Iterable<? extends JavaFileObject> compilationUnit = fileManager.getJavaFileObjects(javaFile); List<String> options = classpath != null ? Arrays.asList("-classpath", classpath) : null; StringWriter output = new StringWriter(); try { boolean successful = compiler.getTask(output, fileManager, null, options, null, compilationUnit).call(); if (!successful) { throw new CompilationException("Failed to compile: " + javaFile, output.toString()); } return firstClassFileFrom(javaFile.getParentFile()); } finally { fileManager.close(); } } private File firstClassFileFrom(File directory) { return directory.listFiles(new FilenameFilter() { @Override public boolean accept(File dir, String name) { return name.endsWith(".class"); } })[0]; } 

See https://github.com/jpalomaki/compiler for a webapp executable example.

Answer 2

I met the same question. The reason is not the "-classpath".

my code is:

  String classpath ="xx/WEB-INF/clases "; List<String> options = classpath != null ? Arrays.asList("-d", classpath,"-cp",classpath) : null; CompilationTask task = compiler.getTask(null, javaDinamicoManager, diagnostics, options, null, Arrays.asList(sourceObj)); boolean result = task.call(); 

"result" will return true.

Answer 3

You can fulfill the answer provided for an even more specific question about how to load compiled code dependencies from a web application launched directly from an unextended WAR file (there is no link to link to JAR files - only the class of the loder class knows how to access the classes) : fooobar.com/questions/1484089 / ...