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我想利用JSP表达式语言来评估servlet中的JSP EL表达式。 理想情况下,我想使用与JSP中使用的完全相同的ExpressionFactory和上下文,以便访问常见的JSP EL变量,如$ {param.myParam}或$ {cookie.myCookie}。如何评估servlet中的JSP EL表达式
到目前为止,我想出了以下内容:
package test;
import java.io.IOException;
import javax.el.ELContext;
import javax.el.ExpressionFactory;
import javax.el.StandardELContext;
import javax.el.ValueExpression;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspApplicationContext;
import javax.servlet.jsp.JspFactory;
@WebServlet(name = "NewServlet", urlPatterns = {"/NewServlet"})
public class NewServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/plain;charset=UTF-8");
ServletContext svc = getServletContext();
JspFactory jspf = JspFactory.getDefaultFactory();
JspApplicationContext jspContext = jspf.getJspApplicationContext(svc);
ExpressionFactory expressionFactory = jspContext.getExpressionFactory();
ELContext context = new StandardELContext(expressionFactory);
ValueExpression expression = expressionFactory.createValueExpression(context, "hello ${param.x}", Object.class);
response.getWriter().println(expression.getValue(context));
}
}
其失败:
ELResolver cannot handle a null base Object with identifier 'param'
的问题似乎在于找到适当的ELContext。
谢谢,我甚至不知道这样一类的存在。这无疑是正确的轨道上,但是这失败: 显示java.lang.NullPointerException 在javax.servlet.jsp.el.ImplicitObjectELResolver $ ImplicitObjects.getImplicitObjects(ImplicitObjectELResolver.java:612) 一些更神奇似乎有需要以便ImplicitObjectELResolver访问隐式对象。 – Remi
我改编了我的答案 –
很好,这个作品,感谢魔术! – Remi