java - 如何解决java9中的模块读取包错误

Question

我正在尝试使用 spring-boot 了解 java 9 中的新模块化，因此我想运行一些简单的应用程序，例如:https://github.com/tmatyashovsky/java9-springboot

我正在使用 maven 3.5.0 和 java 9:

Apache Maven 3.5.0 (ff8f5e7444045639af65f6095c62210b5713f426; 2017-04-03T21:39:06+02:00)
Maven home: ~/soft/apache-maven-3.5.0
Java version: 9-ea, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-9-oracle
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "4.4.0-79-generic", arch: "amd64", family: "unix"

问题是我仍然遇到一些异常。这是什么意思以及我应该如何解决它？

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.1:compile (default-compile) on project api: Compilation failure: Compilation failure: 
[ERROR] module  reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.core reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.jcl reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.aop reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.expression reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.starter.web reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.starter reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.autoconfigure reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.starter.logging reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module logback.classic reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module logback.core reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module slf4j.api reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jul.to.slf4j reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module log4j.over.slf4j reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.starter.json reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.databind reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.annotations reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.core reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.datatype.jdk8 reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.datatype.jsr310 reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jackson.module.parameter.names reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.boot.starter.tomcat reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module tomcat.embed.core reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module tomcat.embed.el reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module tomcat.embed.websocket reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module hibernate.validator reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module validation.api reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module jboss.logging reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module classmate reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.web reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.webmvc reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.context reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module spring.beans reads package javax.annotation from both tomcat.embed.core and java.xml.ws.annotation
[ERROR] module com.lohika.morning.java9modules.service reads package javax.annotation from both java.xml.ws.annotation and tomcat.embed.core

Answer 1

问题是您的模块路径在不同模块(java.xml.ws.annotation 和 tomcat.embed.core)中包含相同的包(javax.annotation)，模块系统禁止这样做，以使配置更可靠。这称为 split package 。当列出所有读取(即“看到”)该包两次的模块时，模块系统会告诉您同样多的信息。那么现在该怎么办？

首要任务是检查两个包是否包含相同的类。如果是，那么你很幸运。现在您需要做的就是确保模块系统只看到其中之一，这有两种可能性:

• 如果在其中一个模块中，您只需要一个包而无需其他任何东西，请将其从您的配置中取出并使用另一个包。也许您可以停止明确要求​​java.xml.ws.annotation？
• 如果将tomcat.embed.core放在类路径上，其包的版本将被完全忽略，整个系统，包括类路径上的代码将只能看到java.xml.ws.annotation中的包。

如果包的两个变体都包含 (a) 另一个不包含的类型以及 (b) 您的应用程序需要的类型，那么您的处境会更困难。首先，这让人怀疑 tomcat.embed.core 做了一些可疑的事情(尽管我对此不确定)。我知道唯一可以提供帮助的可能是 non-standard javac option --patch-module .