Maven exec:java在NPE中运行可执行插件依赖项jar结果 [英] Maven exec:java run executable plugin dependency jar results in NPE

问题描述

我正在制作一个使用sparql端点服务的Maven应用程序.我想要一个maven目标来下载sparql端点并启动服务，但是看来maven在配置类路径时遇到了一些问题.

I'm making a maven application that uses a sparql endpoint service. I'd like to have a maven goal to download the sparql endpoint and start the service but it seems that maven have some problems to configure the classpath.

我在 https://mvnrepository.com/上使用blazegraph及其工件artifact/com.blazegraph/bigdata-jar .

这是pom.xml中我的插件配置:

Here it is my plug-in configuration in pom.xml:

<plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.6.0</version>
            <executions>
                <execution>
                    <goals>
                        <goal>java</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <mainClass>com.bigdata.rdf.sail.webapp.StandaloneNanoSparqlServer</mainClass>
                <includePluginDependencies>true</includePluginDependencies>
                <includeProjectDependencies>false</includeProjectDependencies>
                <executableDependency>
                    <groupId>com.blazegraph</groupId>
                    <artifactId>blazegraph-jar</artifactId>
                </executableDependency>
                <addOutputToClasspath>false</addOutputToClasspath>
            </configuration>
            <dependencies>
                <!-- https://mvnrepository.com/artifact/com.blazegraph/blazegraph-jar -->
                <dependency>
                    <groupId>com.blazegraph</groupId>
                    <artifactId>blazegraph-jar</artifactId>
                    <version>2.1.4</version>
                    <scope>runtime</scope>
                    <type>jar</type>
                </dependency>
            </dependencies>
        </plugin>

debug输出提示插件找不到工件:

The debug output hints that the plug-in can't find the artifact:

Caused by: java.lang.NullPointerException
at org.codehaus.mojo.exec.AbstractExecMojo.findExecutableArtifact(AbstractExecMojo.java:278)
at org.codehaus.mojo.exec.ExecJavaMojo.determineRelevantPluginDependencies(ExecJavaMojo.java:650)
at org.codehaus.mojo.exec.ExecJavaMojo.addRelevantPluginDependenciesToClasspath(ExecJavaMojo.java:568)
at org.codehaus.mojo.exec.ExecJavaMojo.getClassLoader(ExecJavaMojo.java:520)
at org.codehaus.mojo.exec.ExecJavaMojo.execute(ExecJavaMojo.java:301)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
... 27 more

我想念什么?

编辑1 这个问题与什么是NullPointerException无关，以及我该如何解决?因为Maven抛出了异常，因为它在依赖项列表中找不到正确的工件(但应该如此).

Edit 1 This question is not a duplicate of What is a NullPointerException, and how do I fix it? because the exception is thrown by Maven since it can't find the right artifact in the list of dependencies (but it should).

编辑2 感谢@Sean Patrick Floyd，我已部分解决了该问题.我猜类路径配置中仍然存在一些问题.现在，Maven找到了主类和jar，但是执行后，我在编译代码中得到了另一个NPE.在blazegraph的开源代码中，看来它无法在可执行jar中打开资源.

Edit 2 Thanks to @Sean Patrick Floyd I've partially solved the issue. There are still some problem in the classpath configuration, I guess. Now Maven finds the main class and the jar but after the execution I get an other NPE in compiled code. Looking in the open source code of blazegraph it seems that it can't open a resource inside the executable jar.

以下是引起NPE的行:

Here is the line that causes NPE:

System.setProperty("jetty.home",
            jettyXml.getClass().getResource("/war").toExternalForm());

https://github.com/blazegraph/database/blob/master/bigdata-jar/src/main/java/com/bigdata/rdf/sail/webapp/StandaloneNanoSparqlServer.java#L142

推荐答案

< executableDependency> 机制用于二进制文件，而不用于JAR，即

The <executableDependency> mechanism is used for binaries, not for JARs, see the usage page. Remove that part, these settings should be sufficient:

<mainClass>com.bigdata.rdf.sail.webapp.StandaloneNanoSparqlServer</mainClass>
<includePluginDependencies>true</includePluginDependencies>

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