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- 《Maven依赖加载错误的情况分析》
- 《Java Web工程转换为基于Maven的Web工程》
- 《Maven Web工程运行异常:Maven.multiModuleProjectDirectory system propery is not set的问题》
- 《Maven运行异常:Exception in thread “main” java.lang.UnsupportedClassVersionError》
1.0 背景
maven工程在部署时,有时候大家会碰到这种情况:自己在POM中标明的是引用版本A的jar包,实际打包后却是引用版本B的jar包。下面就以我遇到的情形来说明。
2.0 实例说明
2.1 案例
案例:pom中指定httpclient-4.4.jar,但实际打包后加载的是httpclient-4.3.6.jar
这个情况之前一直没有发现,直到最近在集成阿里云oss功能才有所察觉。因为每次部署线上服务器时,总是报如下异常:
---- [http-nio--exec-] [org.apache.catalina.core.ContainerBase.[Tomcat].[localhost].[/].[dispatcherServlet]] [ERROR] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler processing failed; nested exception is java.lang.NoClassDefFoundError: org/apache/http/conn/ssl/NoopHostnameVerifier] with root cause
java.lang.ClassNotFoundException: org.apache.http.conn.ssl.NoopHostnameVerifier
at java.net.URLClassLoader$run(URLClassLoader.java:)
at java.net.URLClassLoader$run(URLClassLoader.java:)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:)
at java.lang.ClassLoader.loadClass(ClassLoader.java:)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:)
at java.lang.ClassLoader.loadClass(ClassLoader.java:)
at com.aliyun.oss.common.comm.DefaultServiceClient.createHttpClientConnectionManager(DefaultServiceClient.java:)
at com.aliyun.oss.common.comm.DefaultServiceClient.<init>(DefaultServiceClient.java:)
at com.aliyun.oss.OSSClient.<init>(OSSClient.java:)
at com.aliyun.oss.OSSClient.<init>(OSSClient.java:)
at com.autonavi.oss.client.DefaultOSSClient.<clinit>(DefaultOSSClient.java:)
at com.autonavi.oss.put.OSSUpload.put2(OSSUpload.java:)
at com.autonavi.utils.gaokuai.FileUpload.fileUpload(FileUpload.java:)
上面这个异常是说明缺少NoopHostnameVerifier这个类。查了下,这个类是httpclient-4.4.jar版本中的类。
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsICN3QTM1UTMzIDOwMDM2EDMy8CX0Vmbu4GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.jpg)
工程的pom中明明已经制定了httpclient-4.4.jar的版本,按道理应该不会出现找不到类的异常。
到目前为止,可以判断是maven依赖冲突,既然有冲突,需要找到冲突的源在哪个依赖,然后过滤掉这个依赖即可。接下来进入本地的工程目录,执行以下命令,获取依赖树:
mvn dependency:tree -Dverbose
注意不能仅仅是mvn dependency:tree这个命令,因为这样看不出深层次的依赖引用关系,后面必须加上-Dverbose,以下为依赖树截取部分,从中可以看出aliyun-sdk-oss-2.1.0:jar包依赖httpclient-4.3.6.jar的包。
com.aliyun.oss:aliyun-sdk-oss:jar::compile
[INFO] | +- (org.apache.httpcomponents:httpclient:jar::compile - version managed from ; omitted for conflict with )
[INFO] | +- org.jdom:jdom:jar::compile
[INFO] | \- net.sf.json-lib:json-lib:jar:jdk15::compile
[INFO] | +- commons-beanutils:commons-beanutils:jar::compile (version managed from )
[INFO] | | \- (commons-collections:commons-collections:jar::compile - omitted for duplicate)
接下来,我们先在pom中过滤掉这个httpclient-4.3.6.jar的包:
<!-- OSS Java SDK -->
<dependency>
<groupId>com.aliyun.oss</groupId>
<artifactId>aliyun-sdk-oss</artifactId>
<version></version>
<exclusions>
<exclusion> <groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
</exclusion>
</exclusions>
</dependency>
注意,过滤掉冲突jar包,使用如下标注:
<exclusions>
<exclusion>
<groupId></groupId>
<artifactId></artifactId>
</exclusion>
</exclusions>
过滤掉后,重新执行mvn dependency:tree -Dverbose,得到的依赖树里面再没有说引用httpclient-4.3.6.jar,然后依次执行mvn clean和mvn install -Dmaven.test.skip=true,target中得到如下文件:
解压:
发现里面的lib目录依然加载的是httpclient-4.3.6.jar,这下子晕了,究竟问题出在哪里,这个maven工程干嘛一直加载这个版本的httpclient包。
至此,可以判断,问题的根结不是在pom依赖上面。而是其他位置,我尝试删除本地库中的httpclient-4.3.6.jar的包。然后重新执行上述maven构建命令,发现工程会自动加载这个版本的包,会不会是打包插件版本的问题:
[INFO]
[INFO] --- spring-boot-maven-plugin:.RELEASE:repackage (default) @ rus-api-services ---
[INFO]
[INFO] --- maven-assembly-plugin:-beta-:single (make-assembly) @ rus-api-services ---
[INFO] Reading assembly descriptor: src/main/assembly/assembly.xml
Downloading: https://repo.maven.apache.org/maven2/org/apache/httpcomponents/httpclient/4.3.6/httpclient-4.3.6.pom
Downloaded: https://repo.maven.apache.org/maven2/org/apache/httpcomponents/httpclient/4.3.6/httpclient-4.3.6.pom (6 KB at 1.9 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/apache/httpcomponents/httpclient/4.3.6/httpclient-4.3.6.jar
Downloaded: https://repo.maven.apache.org/maven2/org/apache/httpcomponents/httpclient/4.3.6/httpclient-4.3.6.jar (579 KB at 157.6 KB/sec)
[INFO] Building tar : /Users/xiaolong/Documents/workspace/rus-api-services/target/rus-api-services.tar.gz
[INFO]
[INFO] --- maven-install-plugin::install (default-install) @ rus-api-services ---
pom中配置的打包插件maven-assembly-plugin如下,版本是2.2-beta-5:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>-beta-</version>
<configuration>
<!-- 应用名(最后压缩包的名字)这个和你申请的应用名称一致 -->
<finalName>rus-api-services</finalName>
<appendAssemblyId>false</appendAssemblyId>
<descriptors>
<descriptor>src/main/assembly/assembly.xml</descriptor>
</descriptors>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
在网上查了下,其最新版本是2.5.3,2.2-beta-5版本有点老了,好了,先替换为新版本,试一试,果然加载了正确的httpclient-4.4.jar。
最后部署线上环境,服务运行OK。