问题:你想和JSTL共同工作。比如,在用自己的标签处理一些逻辑之后,让JSTL处理余下的工作。 看这个JSP例子: <% String name="diego"; request.setAttribute("name",name); %> <c:out value="${name}"/> ...... 许多JSTL标签支持El表达式,所以,只要你在自己的标签内部把值塞进request,其他jstl标签就能使用它们 下面这个例子,从request里面取得对象,找到它属性的值,塞到request里去。 package diegoyun; import javax.servlet.jsp.JspException; import javax.servlet.jsp.tagext.TagSupport; import org.apache.commons.beanutils.PropertyUtils; import org.apache.taglibs.standard.lang.support.ExpressionEvaluatorManager; public class SetVarTag extends TagSupport { private Object value = null; private String property = null; private String var = null; public void setVar(String var) { this.var = var; } public void setProperty(String property) { this.property = property; } public void setValue(Object value)throws JspException{ this.value = ExpressionEvaluatorManager.evaluate( "value", value.toString(), Object.class, this, pageContext); } public int doEndTag() throws JspException{ Object propertyValue = null; try{ propertyValue = PropertyUtils.getProperty(value, property); } catch (Exception e) { throw new JspException(e); } pageContext.setAttribute(var,propertyValue); return EVAL_PAGE; } } 编写TLD <!--SetVarTag--> <tag> <name>set</name> <tag-class>diegoyun.SetVarTag</tag-class> <body-content>empty</body-content> <attribute> <name>value</name> <required>true</required> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>property</name> <required>false</required> <rtexprvalue>false</rtexprvalue> </attribute> <attribute> <name>var</name> <required>false</required> <rtexprvalue>false</rtexprvalue> </attribute> </tag> 编写JSP <%@ page language="java" %> <%@ page import="diegoyun.vo.*"%> <%@ taglib uri="/WEB-INF/tlds/diego.tld" prefix="diego"%> <%@ taglib uri="/WEB-INF/tlds/c.tld" prefix="c"%> <html> <body bgcolor="#FFFFFF"> <% Man man = new Man(); man.setName("diego"); request.setAttribute("man",man); %> Get value from request and set it's property value into request:<br> <diego:set value="${man}" property="name" var="myname"/> now use OutTag of jstl taglib to get the name:<br> value is : <c:out value="${myname}" /> </body> </html> 运行,效果如下: Get value from request and set it's property value into request: now use OutTag of jstl taglib to get the name: value is : diego 结束语 和JSTL交互是非常有用的技术。在JSTL里提供了许多完成基本功能的标签,如输出,循环,条件选择等。仅在处理自己特定逻辑的时候才实现自己的标签,并提供和jstl交互,能大大提高重用性和减少工作量。 |
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