JSTL——添加参数调用

Question

我在 JSTL 中有以下代码可以在 j2ee 站点中检索学生图片

 <c:if test="${student.studentPictureId != null}">
        <a href="javascript:showImage('<c:out value="${student.studentId}"/>','<c:out value="${student.studentPictureId }"/>
</c:if>

我想让代码更通用
而不是调用

 student.studentPictureId

我想用枚举调用通用函数:
学生 class 的函数签名如下：

  Student class  
           String getPictureId(PictureTypeEnum picture type)

所以最终的 JSTL 代码将是这样的：

  <c:if test="${student.getPictureId(PictureTypeEnum.StudentCard) != null}">
        <a href="javascript:showImage('<c:out value="${student.studentId}"/>','<c:out value="${student.getPictureId(PictureTypeEnum.StudentCard)}"/>
</c:if>

我知道打电话时

 <c:out value="${student.studentPictureId }"/>

它基本上是在调用 getter、student.getStudentPictureId() student.studentPictureId

但是是否可以调用学生对象方法并向其传递参数？

Answer 1

不可能直接从 JSTL 调用方法，所以我使用了一种 hack：QuickMap：

public abstract class QuickMap<K,V> implements Map<K,V> {
    @Override
    public abstract V get(Object key);

    @Override
    public final int size() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final boolean isEmpty() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final boolean containsKey(Object key) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final boolean containsValue(Object value) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final V put(K key, V value) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final V remove(Object key) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final void putAll(Map<? extends K, ? extends V> m) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final void clear() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final Set<K> keySet() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final Collection<V> values() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    @Override
    public final Set<Entry<K, V>> entrySet() {
        throw new UnsupportedOperationException("Not supported yet.");
    }
}

对于你的情况，我会在你的学生中添加以下方法 class:

public Map<Object,String> getStudentPictureIds() {
    return new QuickMap<Object,String>() {
        @Override
        public String get(Object k) {
            PictureTypeEnum type;
            if (k instanceof PictureTypeEnum) {
                type = (PictureTypeEnum)k; 
            } else {
                type = PictureTypeEnum.valueOf(k.toString());
            }
            return getStudentPictureId(type);
        }            
    };
}

并不是说使用 JSTL 操作枚举并不容易，所以该方法也接受字符串。

您将在 JSP 中按如下方式使用它：

<c:out value="${student.pictureIds['StudentCard']}"/>

JSTL——添加参数调用

JSTL - add parameters to call

java

jstl

el

jstl-functions