使用 param 标签抑制空参数

2022-01-16 00:00:00 url-parameters java jsp struts2

我编写了用于许多操作的 JSP.它有一个参数链接

I have written JSP that I used with many actions. It has a link with parameters

链接:

<s:a namespace="/some" action="view">
  <s:param name="purpose" value="%{purpose}"/>
  <s:param name="type" value="%{type}"/>
  <s:property value="%{name}"/>
</s:a>

动作类:

public class ViewAction extends ActionSupport {

  private Long purpose;
  private Long type;
  private String name;

  public Long getPurpose() {
    return purpose;
  }

  public void setPurpose(Long purpose) {
    this.purpose = purpose;
  }

  public Long getType() {
    return type;
  }

  public void setType(Long type) {
    this.type = type;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
}

通常我会初始化两个参数，但有时一个参数是null.所以，链接是用 href 生成的，比如

Usually I initialize both parameters, but sometimes one parameter is null. So, the link is generated with href like

/context/some/view?purpose=1&type=

但我想删除 &type=

我尝试了 Param 示例.

<s:a namespace="/some" action="view">
  <s:param name="purpose" value="%{purpose}"/>
  <s:param name="type" value="%{type}"/>
  <s:property value="%{name}"/>
  <s:param name="suppressEmptyParameters" value="true"/>
</s:a>

但是没用

我也试过了

<s:a namespace="/some" action="view">
  <s:param name="purpose" value="%{purpose}"/>
  <s:param name="type" value="%{type}" suppressEmptyParameters="true"/>
  <s:property value="%{name}"/>
</s:a>

我得到了

java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.String
    at org.apache.struts2.components.Param.end(Param.java:129)
    at org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:42)

如何解决这个问题?

推荐答案

那行 <s:param name="suppressEmptyParameters" value="true"/> 没有意义，并且应该从 <s:param> 文档中删除.

Well that line <s:param name="suppressEmptyParameters" value="true"/> doesn't make sense, and it should be removed from the <s:param> docs.

<s:param name="type" value="%{type}" suppressEmptyParameters="true"/> 是抑制空参数的正确方法，但它不起作用由于错误 WW-4275 而不是 String-s.

The <s:param name="type" value="%{type}" suppressEmptyParameters="true"/> is correct way of suppressing empty parameters and it isn't working with not String-s because of the bug WW-4275.

同时，在下一个版本发布之前，您可以使用toString()方法来避免ClassCastException异常.

Meanwhile, until the next version is released, you can use toString() method to avoid ClassCastException exception.

<s:param name="type" value="type.toString()" suppressEmptyParameters="true"/>

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