Apache Commons EL

Apache Commons EL
直接使用 JSTL Expression Language

import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.el.ExpressionEvaluator;
import javax.servlet.jsp.el.VariableResolver;

import org.apache.commons.el.ExpressionEvaluatorImpl;
import org.apache.commons.el.VariableResolverImpl;

public class Main {
  public static void main(String[] args) throws Exception {

    PageContext pc = new PageContext() {
      Map map = new HashMap();
      VariableResolver pResolver = new VariableResolverImpl(this);

      public void forward(String arg0) throws ServletException,
          IOException {
      }

      public Exception getException() {
        return null;
      }

      public Object getPage() {
        return null;
      }

      public ServletRequest getRequest() {
        return null;
      }

      public ServletResponse getResponse() {
        return null;
      }

      public ServletConfig getServletConfig() {
        return null;
      }

      public ServletContext getServletContext() {
        return null;
      }

      public HttpSession getSession() {
        return null;
      }

      public void handlePageException(Exception arg0)
          throws ServletException, IOException {

      }

      public void handlePageException(Throwable arg0)
          throws ServletException, IOException {

      }

      public void include(String arg0) throws ServletException,
          IOException {

      }

      public void include(String arg0, boolean arg1)
          throws ServletException, IOException {

      }

      public void initialize(Servlet arg0, ServletRequest arg1,
          ServletResponse arg2, String arg3, boolean arg4, int arg5,
          boolean arg6) throws IOException, IllegalStateException,
          IllegalArgumentException {

      }

      public void release() {

      }

      public Object findAttribute(String key) {
        return map.get(key);
      }

      public Object getAttribute(String key) {
        return map.get(key);
      }

      public Object getAttribute(String key, int arg1) {
        return map.get(key);
      }

      public Enumeration getAttributeNamesInScope(int arg0) {
        return java.util.Collections.enumeration(map.keySet());
      }

      public int getAttributesScope(String arg0) {
        return 0;
      }

      public ExpressionEvaluator getExpressionEvaluator() {
        return null;
      }

      public JspWriter getOut() {
        return null;
      }

      public VariableResolver getVariableResolver() {
        return pResolver;
      }

      public void removeAttribute(String key) {
        map.remove(key);
      }

      public void removeAttribute(String key, int arg1) {
        map.remove(key);
      }

      public void setAttribute(String key, Object value) {
        map.put(key, value);
      }

      public void setAttribute(String key, Object value, int arg2) {
        map.put(key, value);
      }

    };

    pc.setAttribute("v", "World");
    pc.setAttribute("x", "2");
    pc.setAttribute("sysProp", System.getProperties());
    pc.setAttribute("x.y", "requestScope x.y value");

    StringBuilder sb = new StringBuilder();
    sb.append("Hello ${v}!\n");
    sb.append("5 - ${x} = ${5-x}\n");
    sb.append("ava.version = ${sysProp['java.version']}\n");
    sb.append("${requestScope['x.y']}\n");

    ExpressionEvaluator ee = new ExpressionEvaluatorImpl();

    Object s = ee.evaluate(sb.toString(), String.class, pc
        .getVariableResolver(), null);

    System.out.println(s);
  }
}
/*
Hello World!
5 - 2 = 3
ava.version = 1.6.0_13
requestScope x.y value
*/