根据条件在ant中复制文件

Question

如果在 ant 目标中设置了属性，我必须复制一个文件，但我总是收到此代码的错误：

<condition property="component.is.x">
  <equals arg1="${COMPONENT_ID}" arg2="x" />
</condition>
<target name="copyschemaparamsfile" if="sql.file.present" >
  <if>
    <equals arg1="${component.is.x}" arg2="true" />
    <then>
      <copy file="${in.root}/schema/${COMPONENT_ID}-schema.sql"
            tofile="${tmp.dir}/${COMPONENT_ID}/x/schema/schema.sql" 
            failonerror="false" />
    </then>
    <else>
      <copy file="${inf.root}/schema/${COMPONENT_ID}-schema.sql"
            tofile="${tmp.dir}/${COMPONENT_ID}/${COMPONENT_ID}/schema/schema.sql" failonerror="false" />
    </else>
  </if>
</target>

错误是：

Ant could not find the task or a class this task relies upon.
This is common and has a number of causes; the usual
    solutions are to read the manual pages then download and
    install needed JAR files, or fix the build file:
     - You have misspelt 'if'.
       Fix: check your spelling.
     - The task needs an external JAR file to execute
         and this is not found at the right place in the classpath.
       Fix: check the documentation for dependencies.
       Fix: declare the task.
     - The task is an Ant optional task and the JAR file and/or libraries
         implementing the functionality were not found at the time you
         yourself built your installation of Ant from the Ant sources.
       Fix: Look in the ANT_HOME/lib for the 'ant-' JAR corresponding to the
         task and make sure it contains more than merely a META-INF/MANIFEST.MF.
         If all it contains is the manifest, then rebuild Ant with the needed
         libraries present in ${ant.home}/lib/optional/ , or alternatively,
         download a pre-built release version from apache.org
     - The build file was written for a later version of Ant
       Fix: upgrade to at least the latest release version of Ant
     - The task is not an Ant core or optional task
         and needs to be declared using <taskdef>.
     - You are attempting to use a task defined using
        <presetdef> or <macrodef> but have spelt wrong or not
       defined it at the point of use

    Remember that for JAR files to be visible to Ant tasks implemented
    in ANT_HOME/lib, the files must be in the same directory or on the
    classpath

我在执行时总是遇到错误。有人可以建议如何在 ant 目标中检查参数并从一个目录复制到另一个目录吗？

Answer 1

Ant <if/> 是 Ant-Contrib 的一部分。要使用，请按照Ant-Contrib Tasks installation page 上的说明进行操作：

(1) 将ant-contrib-0.3.jar复制到你的Ant的lib目录下 安装。如果您想在自己的项目中使用其中一项任务， 添加行

<taskdef resource="net/sf/antcontrib/antcontrib.properties"/>

到您的构建文件。

(2) 将 ant-contrib-0.3.jar 保存在单独的位置。你现在必须 明确告诉 Ant 在哪里可以找到它（比如在 /usr/share/java/lib 中）：

<taskdef resource="net/sf/antcontrib/antcontrib.properties">
  <classpath>
    <pathelement location="/usr/share/java/lib/ant-contrib-0.3.jar"/>
  </classpath>
</taskdef>