起因

在tomcat启动时，总会报Name [UserDatabase] is not bound in this Context这一异常，但是也不会影响tomcat中程序的正常运行，但总是报异常不解决看着也难受，在这里记录下解决的过程。

异常代码

Caused by: org.apache.catalina.LifecycleException: No UserDatabase component found under key [UserDatabase]
    at org.apache.catalina.realm.UserDatabaseRealm.startInternal(UserDatabaseRealm.java:239)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    ... 17 more

思路

从异常代码中可以看出，应该是缺少UserDatabase这一组件（配置）。以此为出发点，联想到Tomcat的Server.xml中有UserDatabase这一配置项。所以开始检查conf/server.xml文件。

通过检查conf/server.xml文件，找到了UserDatabase的配置项及其引用，代码如下：

配置项

  <!-- Global JNDI resources
       Documentation at /docs/jndi-resources-howto.html
  -->
  <GlobalNamingResources>
    <!-- Editable user database that can also be used by
         UserDatabaseRealm to authenticate users
    -->
    <Resource name="UserDatabase" auth="Container"
              type="org.apache.catalina.UserDatabase"
              description="User database that can be updated and saved"
              factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
              pathname="conf/tomcat-users.xml" />
  </GlobalNamingResources>

引用

      <!-- Use the LockOutRealm to prevent attempts to guess user passwords
           via a brute-force attack -->
      <Realm className="org.apache.catalina.realm.LockOutRealm">
        <!-- This Realm uses the UserDatabase configured in the global JNDI
             resources under the key "UserDatabase".  Any edits
             that are performed against this UserDatabase are immediately
             available for use by the Realm.  -->
        <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
               resourceName="UserDatabase"/>
      </Realm>

解决办法

1. 首先查看是否正常引用UserDatabase；
2. 如果引用了UserDatabase，再查看server.xml文件中是否存在其配置项；