我有一个保存结果的Bean。我需要使用JSTL对其进行迭代并呈现结果。这是豆子：

public class DetResults
{
    private List<String> headings;
    private List<Class<?>> types;
    private List<Object[]> data;

    public DetResults() {}

    public List<String> getHeadings() { return this.headings; }
    public String getHeading(int which) { return this.headings.get(which); }

    public List<Class<?>> getTypes() { return this.types; }
    public Class<?> getType(int which) { return this.types.get(which); }

    public List<Object[]> getData( ) { return this.data; }
    public Object[] getDataAtRow( int row ) { return this.data.get(row); }


    public void setHeadings( List<String> val ) { this.headings = val; }
    public void setHeadings( String[] val ) { this.headings = Arrays.asList(val); }
    public void addHeading( String val ) 
    { 
        if( this.headings == null ) this.headings = new ArrayList<String>();
        this.headings.add(val); 
    }

    public void setTypes( List<Class<?>> val ) { this.types = val; }
    public void setTypes( Class<?> val[] ) { this.types = Arrays.asList(val); }
    public void addType( Class<?> val ) 
    {
        if( this.types == null ) this.types = new ArrayList<Class<?>>();
        this.types.add(val); 
    }


    public void setData( List<Object[]> val ) { this.data = val; }

    // allow NPE to get thrown
    public void setDataAtRow( Object[] val, int row ) { this.data.set(row, val); }

    public void appendDataRow( Object[] val ) 
    {
        if( data == null ) data = new ArrayList<Object[]>(); 
        this.data.add(val); 
    }

    public int getColumnCount() { return this.headings!=null?this.headings.size():0; }

}

这是将bean设置为JSP的处理程序：

DetResults results = detDAO.fetchDetResults(paramBean);
request.setAttribute("results", results);
action.setJspURI(".../.jsp");

我试图显示如下：

<c:forEach var="results" items="${results}">
    ${results.heading}
</c:forEach>

但这引发了以下异常：

原因：javax.servlet.ServletException：javax.servlet.jsp.JspTagException：不知道如何迭代中提供的“项目”

如果我将结果记录在我的处理程序页面上，如下所示：

System.out.println( "\n\nthere are " + results.getColumnCount() + " columns in the result set" );
for( int i=0; i<results.getColumnCount(); i++ )
{
    System.out.println( results.getHeading(i) + " --> " + results.getType(i) );
}

日志记录似乎在服务器上显示正常。