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Unable to locate Spring NamespaceHandler for XML schema namespace

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使用“assembly”插件构建一个胖JAR包，加载该胖JAR包执行后，出现如下错误：

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Caused by: org.springframework.beans.factory.parsing.BeanDefinitionParsingException: Configuration problem: Unable to locate Spring NamespaceHandler for XML schema namespace [http://www.springframework.org/schema/p]

一般出现Unable to locate Spring NamespaceHandler for XML schema namespace错误的原因是缺少对相应Spring 包（比如“spring-core”）的依赖，但是这里经过确认，所有需要的Spring包都被正确依赖。
根据[1]可知，使用“assembly”插件构建胖JAR包时，目标胖JAR包中“META-INF”子目录下的“spring.schemas”和“spring.handlers”文件内容可能由于“互相覆盖”而缺失所需的Spring相关内容并最终导致出现Unable to locate Spring NamespaceHandler for XML schema namespace错误，验证我们这里所生成胖JAR包内上述两个文件的内容，发现果然缺失了所需的Spring相关内容。

“spring.schemas”文件内容如下：

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http\://www.alibaba.com/schema/stat.xsd=META-INF/stat.xsd

“spring.handlers”文件内容如下：

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http\://www.alibaba.com/schema/stat=com.alibaba.druid.support.spring.stat.config.DruidStatNamespaceHandler

接下来使用“shade”插件构建胖JAR包，且配置目标胖JAR包中“META-INF”子目录下“spring.schemas”和“spring.handlers”文件的生成策略是“合并”而非“互相覆盖”，具体插件配置如下： 
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<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>2.4</version>
    <executions>
      <execution>
        <phase>package</phase>
        <goals>
          <goal>shade</goal>
        </goals>
        <configuration>
          <transformers>
            <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
              <resource>META-INF/spring.handlers</resource>
            </transformer>
            <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
              <resource>META-INF/spring.schemas</resource>
            </transformer>
          </transformers>
        </configuration>
      </execution>
    </executions>
</plugin>
构建新胖JAR包，现在构建得胖JAR包中“META-INF”子目录下的“spring.schemas”和“spring.handlers”文件内容正确保留了所需的Spring相关内容，加载该胖JAR包执行不再出现`Unable to locate Spring NamespaceHandler for XML schema namespace`错误。

“spring.schemas”文件内容如下：

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http\://www.alibaba.com/schema/stat.xsd=META-INF/stat.xsd
http\://www.springframework.org/schema/beans/spring-beans-2.0.xsd=org/springframework/beans/factory/xml/spring-beans-2.0.xsd
http\://www.springframework.org/schema/beans/spring-beans-2.5.xsd=org/springframework/beans/factory/xml/spring-beans-2.5.xsd
http\://www.springframework.org/schema/beans/spring-beans-3.0.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd
http\://www.springframework.org/schema/beans/spring-beans.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd
http\://www.springframework.org/schema/tool/spring-tool-2.0.xsd=org/springframework/beans/factory/xml/spring-tool-2.0.xsd
http\://www.springframework.org/schema/tool/spring-tool-2.5.xsd=org/springframework/beans/factory/xml/spring-tool-2.5.xsd
http\://www.springframework.org/schema/tool/spring-tool-3.0.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd
http\://www.springframework.org/schema/tool/spring-tool.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd
http\://www.springframework.org/schema/util/spring-util-2.0.xsd=org/springframework/beans/factory/xml/spring-util-2.0.xsd
http\://www.springframework.org/schema/util/spring-util-2.5.xsd=org/springframework/beans/factory/xml/spring-util-2.5.xsd
http\://www.springframework.org/schema/util/spring-util-3.0.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd
http\://www.springframework.org/schema/util/spring-util.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd
...（篇幅所限，以上只是部分文件内容）

“spring.handlers”文件内容如下：

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http\://www.alibaba.com/schema/stat=com.alibaba.druid.support.spring.stat.config.DruidStatNamespaceHandler
http\://www.springframework.org/schema/p=org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler
http\://www.springframework.org/schema/util=org.springframework.beans.factory.xml.UtilNamespaceHandler

http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler
http\://www.springframework.org/schema/jee=org.springframework.ejb.config.JeeNamespaceHandler
http\://www.springframework.org/schema/lang=org.springframework.scripting.config.LangNamespaceHandler
http\://www.springframework.org/schema/task=org.springframework.scheduling.config.TaskNamespaceHandler

http\://www.springframework.org/schema/aop=org.springframework.aop.config.AopNamespaceHandler

**参考文献：** [1]https://stackoverflow.com/questions/31892587/spring-4-2-dependancy-injection-http-www-springframework-org-schema-p-erro
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