姓张的小子

使用Spring依赖注入实现方法替换

Posted by eDWARD at 15:42

　　在ApplicationContext配置文件中配置Bean的时候可以使用replaced-method设置需要替换的方法。replaced-method标签的name属性用来设置需要替换的方法名称，replacer属性用来设置替换方法的Bean，前提是这个Bean需要实现Spring的MethodReplacer接口，replaced-method标签下的元素arg-type用来区分替换方法的参数。

需要替换方法的Class

public class ReplacementTarget {
  public String formatMessage(String msg) {
    return msg;
  }

  public String formatMessage(Object msg) {
    return msg;
  }

  public void foo() {
  }
}

替换方法的CLASS

public class FormatMessageReplacer implements MethodReplacer {
  public Object reimplement(Object target, Method method, Object[] args)
    throws Throwable {
    if (isFormatMessageMethod(method)) {
      String msg = (String) args[0];
      return msg;
    } else {
      throw new IllegalArgumentException("Unable to reimplement method "
        + method.getName());
    }
  }

  // 验证方法是否正确
  private boolean isFormatMessageMethod(Method method) {
    if (method.getParameterTypes().length != 1) {
      return false;
    }

    if (!("formatMessage".equals(method.getName())))
      return false;
    }

    if (method.getReturnType() != String.class) {
      return false;
    }

    if (method.getParameterTypes()[0] != String.class) {
      return false;
    }

    return true;
    }
}

配置文件(replacement.xml)

<beans>
  <bean id="methodReplacer" class="FormatMessageReplacer"/>
    <bean id="replacementTarget" class="ReplacementTarget">
      <replaced -method name="formatMessage" replacer="methodReplacer">
        <arg -type>String</arg>
      </replaced>
    </bean>
  <bean id="standardTarget" class="ReplacementTarget"/>
</beans>

测试类

public class MethodReplacementExample {
  public static void main(String[] args) {
    BeanFactory factory = new XmlBeanFactory(
      new FileSystemResource("build/replacement.xml"));
    ReplacementTarget replacementTarget = (ReplacementTarget)
      factory.getBean("replacementTarget");
    ReplacementTarget standardTarget = (ReplacementTarget)
      factory.getBean("standardTarget");

    // 执行方法
    displayInfo(replacementTarget);
    displayInfo(standardTarget);
  }

  private static void displayInfo(ReplacementTarget target) {
    System.out.println(target.formatMessage("Hello World!"));
  }
}

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