使用阿里云OSS对象储存服务时Java常见问题：包冲突

• 错误原因
  使用OSS Java SDK时，报类似如下错误，说明工程中可能有包冲突。

  Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/http/ssl/TrustStrategy
    at com.aliyun.oss.OSSClient.<init>(OSSClient.java:268)
    at com.aliyun.oss.OSSClient.<init>(OSSClient.java:193)
    at com.aliyun.oss.demo.HelloOSS.main(HelloOSS.java:77)
  Caused by: java.lang.ClassNotFoundException: org.apache.http.ssl.TrustStrategy
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    ... 3 more
  

```java
Exception in thread "main" java.lang.NoSuchFieldError: INSTANCE
 at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:52)
 at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:56)
 at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<clinit>(DefaultHttpRequestWriterFactory.java:46)
 at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:82)
 at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:95)
 at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:104)
 at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<clinit>(ManagedHttpClientConnectionFactory.java:62)
 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager$InternalConnectionFactory.<init>(PoolingHttpClientConnectionManager.java:572)
 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:174)
 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:158)
 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:149)
 at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:125)
 at com.aliyun.oss.common.comm.DefaultServiceClient.createHttpClientConnectionManager(DefaultServiceClient.java:237)
 at com.aliyun.oss.common.comm.DefaultServiceClient.<init>(DefaultServiceClient.java:78)
 at com.aliyun.oss.OSSClient.<init>(OSSClient.java:268)
 at com.aliyun.oss.OSSClient.<init>(OSSClient.java:193)
 at OSSManagerImpl.upload(OSSManagerImpl.java:42)
 at OSSManagerImpl.main(OSSManagerImpl.java:63)

错误原因是OSS Java SDK使用了Apache HttpClient 4.4.1，而您的工程使用了与Apache HttpClient 4.4.1冲突的Apache HttpClient或commons-httpclient jar包。要查看工程使用的jar包及版本，请在您的工程目录下执行mvn dependency:tree。如下图所示，您的工程里使用了Apache HttpClient 4.3：

• 解决方法
  包冲突有以下两种解决方法：

• 使用统一版本。如果您的工程使用与Apache HttpClient 4.4.1冲突的版本，请您使用4.4.1版本，并在pom.xml删除其它版本的Apache HttpClient依赖。如果您的工程使用了commons-httpclient，也可能存在冲突，请删除commons-httpclient。

• 解决依赖冲突。如果您的工程依赖多个第三方包，而第三方包又依赖不同版本的Apache HttpClient，您的工程里会有依赖冲突，请使用exclusion解除。更多信息，请参见Maven Guides。

OSS Java SDK依赖以下版本的包，冲突解决办法与HttpClient类似。

• 免费的容量毕竟有限，有购买云产品需求的可以找微信：xmh607 在官网基础上返现。

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