Maven 构建失败，涉及依赖 JAR 中的 MANIFEST.MF 类路径

Question

First off, I'm a long time user (and beneficiary) of StackOverflow, but this is my first question. I've done plenty of searching on this topic, but most of the articles I've turned up talk about generating JAR files, not working with 3rd party JARs from the Maven Central repo which I don't really have the power to fix. The few solutions I've seen floating around aren't really acceptable.

The problem is that most of the jaxb JARs found in the Maven Central repository contain classpath entries (in the MANIFEST.MF file) that point to dependencies, and those dependencies are specified with relative paths -- typically assuming that dependency bar.jar exists in the same directory as foo.jar.

This is fine if you have all your JAR dependencies in a single lib directory, for example. But:

• Maven wants to maintain its own local repository, so every single packaged JAR lives in its own directory (with each version in a separate subdirectory).
• Maven JARs are typically named with the version info embedded in the filename, whereas the classpath entry in MANIFEST.MF specifies the dependency with just the base filename (no version).

The net result is an error message like this:

[ERROR] bad path element "C:\\Users\\rpoole\\.m2\\repository\\com\\sun\\xml\\bind\\jaxb-impl\\2.2.11\\jaxb-core.jar": no such file or directory

One solution is to write a script or small app to go through all the JARs and strip out the classpath info from the embedded MANIFEST.MF file. But that is not very clean, and requires an extra step before doing the actual build.

Another potential solution is that some newer published versions of the JARs in question have supposedly fixed this classpath problem, so therefore use the latest and greatest. Unfortunately, this app I'm working on is legacy, and is being developed for a 3rd party, so I can't update the dependencies beyond a certain version. So far, all the jaxb JARs that I have poked into seem to have issues.

Is there a way to tell Maven to ignore the embedded classpath in the JAR and only rely on Maven's own dependency resolution? I've tried things like reordering dependencies, but that doesn't work (or moves the build problem from one subproject to another).

One additional annoyance: There is a "blessed" Maven repo we have that seems to let the build complete with no problem, but so far I've been unable to figure out why this particular set of JARs builds OK. I suspect someone may have gone in and tweaked some JARs or POMs manually, but there's scant information, and diff tools aren't really helping much.

Regardless, the project should build from scratch.

What would be nice is if I could specify something like an exclusion block in the pom.xml for the subproject that's breaking, but for dealing with a JAR's embedded classpath instead of Maven's own transitive dependencies (specified by groupId/artifactId).

Edit: Apparently, some people believe that this is impossible, and that Maven ignores the Class-Path entry in Manifest.MF. However, this is a known issue, as discussed in this StackOverflow article . There's also another good article which explains some of the history of this a bit better.

The problem is that I can't go through the JARs and edit the MANIFEST.MF files on each as part of the build process. That's just not a practical approach, even if automated by script. I need a solution that actually will work for code that is already in production. These issues were supposedly fixed in later versions of the JARs in question, but I may not be able to use newer versions of those.

Additionally, one of the proposed fixes is to add -Xlint:-path to the compiler args, which suppresses the error message. However, the build simply fails at another point for me, so at first blush this does not appear to be a good solution either. I'll be trying this again because according to this , the syntax for compiler arguments inside POM files is a bit wonky.

Answer 1

I hate answering my own question, but I finally did manage to get past this problem. For those who keep insisting that Maven builds can't possibly be affected by the Class-Path entry in a jar's MANIFEST.MF, please read this article by Michael Bayne. It summarizes the problem and the solution rather nicely. Hint: javac certainly does care about the embedded classpath in jars.

The trick is to add -Xlint:-path to the compiler arguments, although I was dubious of this solution initially. Doing this will suppress the bad path element warnings/errors, and therefore Maven won't prematurely halt the build. The problem I had was figuring out the correct syntax for embedding these arguments in the pom.xml. That's where this article comes in handy. Therefore, the compiler plugin's configuration has to look like this to be understood properly:

<plugins>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
            <source>${java-version}</source>
            <target>${java-version}</target>
            <compilerArguments>
                <Xlint/>
                <Xlint:-path/>
            </compilerArguments>
            <showWarnings>true</showWarnings>
            <showDeprecation>true</showDeprecation>
        </configuration>
    </plugin>
</plugins>

Note that this syntax is not very good XML (as Bayne points out), and most IDEs will flag the second Xlint line as an error, but it will work with Maven. Using the syntax given in some Maven tutorials may result in the arguments not being passed to the compiler at all, or only the last argument being passed.

Once this problem is taken care of, you may discover other build problems (I certainly did), but at least those problems won't be hidden from you any longer.

Answer 2

The problem is that you are referencing a post which is seven years old..and don't use more recent versions of the maven-compiler-plugin :

The arguments to the javac compiler can better done like this:

<project>
  [...]
  <build>
    [...]
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.6.1</version>
        <configuration>
          <compilerArgs>
            <arg>-Xlint</arg>
            <arg>-Xlint:-path</arg>
          </compilerArgs>
        </configuration>
      </plugin>
    </plugins>
    [...]
  </build>
  [...]
</project>