需要用el表达式取值的数据，除了对象，最好都是String类型，

修改了1小时，将HashMap<Integer , Object> 改为HashMap<String, Object>才解决问题

可以参考下文

jsp EL表达式中令人郁闷的int/float/char

博客分类： 
• java web
• java开发常见问题分析

在EL表达式计算过程中，有朋友会遇到许多奇怪的问题，经常非常郁闷，在此我把这些总结一下，方便查询：

1、所有的整数数字字面量都是Long类型的；

2、所有小数字面量都是Double类型的；

3、""或''声明的是字符串，即''也是字符串，非char；

4、比较时都是equals比较。

 

接下来看几个可能出问题的例子，你会遇到一下的几个呢：

1、

如${1+2147483647} 结果是多少？

如果在java程序里边运行会得到-2147483648，而在jsp el中会得到2147483648。

 

2、

<%

    Map<Object, Object> map = new HashMap<Object, Object>();

    map.put(new Long(1), 123);

    request.setAttribute("map", map);

    request.setAttribute("a", new Long(1));

%>

${map[1]}  正确

${map[a]} 正确

 

3、

<%

    Map<Object, Object> map = new HashMap<Object, Object>();

    map.put(new Integer(1), 123);

    request.setAttribute("map", map);

    request.setAttribute("a", new Long(1));

    request.setAttribute("b", new Integer(1));

%>

${map[1]}  错误

${map[a]}  错误

${map[b]}  正确

 

4、

<%

    Map<Object, Object> map = new HashMap<Object, Object>();

    map.put(1.1, 123); //map.put(1.1d, 123);

    request.setAttribute("map", map);

    request.setAttribute("a", new Double(1.1));

%>

map.a=${map[1.1]}  正确

map.a=${map[a]}     正确

 

5、

<%

    Map<Object, Object> map = new HashMap<Object, Object>();

    map.put(1.1f, 123); //map.put(new Float(1.1), 123);

    request.setAttribute("map", map);

    request.setAttribute("a", new Double(1.1));

    request.setAttribute("b", new Float(1.1));

%>

map.a=${map[1.1]}  错误

map.a=${map[a]}     错误

map.a=${map[b]}     正确

 

6、

结合struts2的ognl表达式

<s:property value="#map = #{'a':123, 'b':234}, ''"/>  --->定义一个map，放入值栈的上下文区

<s:property value="#map['a']"/> ---------->正确，因为其支持char

${map['a']} ------------>错误， 因为'a'在jsp el表达式中是字符串，不能=char。

 

<s:property value='#map = #{"a":123, "b":234}, ""'/>  --->此时key是字符串

${map['a']}

 

此处需要注意ognl中'×××' 如果长度是1那么是Character 否则是String 可参考

http://jinnianshilongnian.iteye.com/blog/1870662

 

补充：

在EL表达式规范2.2中，定义了：

写道

■ The value of an IntegerLiteral ranges from Long.MIN_VALUE to
Long.MAX_VALUE
■ The value of a FloatingPointLiteral ranges from Double.MIN_VALUE to
Double.MAX_VALUE

 在tomcat7.0.6实现中，jasper.jar（实现了EL2.2规范）：

AstFloatingPoint表示小数，AstInteger表示整数，其定义如下：

 public final class AstInteger extends SimpleNode
 {
   private volatile Number number;

   public AstInteger(int id)
   {
     super(id);
   }

   protected Number getInteger()
   {
     if (this.number == null) {
       try {
         this.number = new Long(this.image);
       } catch (ArithmeticException e1) {
         this.number = new BigInteger(this.image);
       }
     }
     return this.number;
   }

   public Class<?> getType(EvaluationContext ctx)
     throws ELException
   {
     return getInteger().getClass();
   }

   public Object getValue(EvaluationContext ctx)
     throws ELException
   {
     return getInteger();
   }
 }

 

 public final class AstFloatingPoint extends SimpleNode
 {
   private volatile Number number;

   public AstFloatingPoint(int id)
   {
     super(id);
   }

   public Number getFloatingPoint()
   {
     if (this.number == null) {
       try {
         this.number = new Double(this.image);
       } catch (ArithmeticException e0) {
         this.number = new BigDecimal(this.image);
       }
     }
     return this.number;
   }

   public Object getValue(EvaluationContext ctx)
     throws ELException
   {
     return getFloatingPoint();
   }

   public Class<?> getType(EvaluationContext ctx)
     throws ELException
   {
     return getFloatingPoint().getClass();
   }
 }

 

+ - * /实现，此处只看+的：

 package org.apache.el.parser;

 import javax.el.ELException;
 import org.apache.el.lang.ELArithmetic;
 import org.apache.el.lang.EvaluationContext;

 public final class AstPlus extends ArithmeticNode
 {
   public AstPlus(int id)
   {
     super(id);
   }

   public Object getValue(EvaluationContext ctx)
     throws ELException
   {
     Object obj0 = this.children[0].getValue(ctx);
     Object obj1 = this.children[1].getValue(ctx);
     return ELArithmetic.add(obj0, obj1);
   }
 }

 其委托给ELArithmetic.add：

 public static final DoubleDelegate DOUBLE = new DoubleDelegate();

  public static final LongDelegate LONG = new LongDelegate();

  private static final Long ZERO = Long.valueOf(0L);

  public static final Number add(Object obj0, Object obj1) {
    if ((obj0 == null) && (obj1 == null))
      return Long.valueOf(0L);
    ELArithmetic delegate;
    if (BIGDECIMAL.matches(obj0, obj1))
      delegate = BIGDECIMAL;
    else if (DOUBLE.matches(obj0, obj1))
      if (BIGINTEGER.matches(obj0, obj1))
        delegate = BIGDECIMAL;
      else
        delegate = DOUBLE;
    else if (BIGINTEGER.matches(obj0, obj1))
      delegate = BIGINTEGER;
    else {
      delegate = LONG;
    }
    Number num0 = delegate.coerce(obj0);
    Number num1 = delegate.coerce(obj1);

    return delegate.add(num0, num1);
  }

 此处委托给了各种delegate计算，其+的实现：

 public static final class LongDelegate extends ELArithmetic
   {
     protected Number add(Number num0, Number num1)
     {
       return Long.valueOf(num0.longValue() + num1.longValue());
     }

 从这里我们可以看出其实现。

 

而且其规范中都规定了具体字面量的东西：

写道

1.3 Literals
There are literals for boolean, integer, floating point, string, and null in an eval-
expression.
■ Boolean - true and false
■ Integer - As defined by the IntegerLiteral construct in Section 1.19
■ Floating point - As defined by the FloatingPointLiteral construct in
Section 1.19
■ String - With single and double quotes - " is escaped as \", ' is escaped as \',
and \ is escaped as \\. Quotes only need to be escaped in a string value enclosed
in the same type of quote
■ Null - null

 

也规定了操作符的运算规则，如+ - *：

 1.3 Literals
 There are literals for boolean, integer, floating point, string, and null in an eval-expression.
   ■ Boolean - true and false
   ■ Integer - As defined by the IntegerLiteral construct in Section 1.19
   ■ Floating point - As defined by the FloatingPointLiteral construct in
 Section 1.19
   ■ String - With single and double quotes - " is escaped as \", ' is escaped as \',and \ is escaped as \\. Quotes only need to be escaped in a string value enclosed in the same type of quote
   ■ Null - null
   ■ If operator is -, return A.subtract(B)
   ■ If operator is *, return A.multiply(B)
   ■ If A or B is a Float, Double,or String containing ., e,or E:
   ■ If A or B is BigInteger, coerce both A and B to BigDecimal and apply operator.
   ■ Otherwise, coerce both A and B to Double and apply operator
   ■ If A or B is BigInteger, coerce both to BigInteger and then:
   ■ If operator is +, return A.add(B)
   ■ If operator is -, return A.subtract(B)
   ■ If operator is *, return A.multiply(B)
   ■ Otherwise coerce both A and B to Long and apply operator
   ■ If operator results in exception, error

如Integer型，直接交给前边介绍的IntegerLiteral。

 

即规范中其实已经规范了这些，但是就像java里的一些东西，虽然规范规定了（如排序时 很多人有时候使用 return a-b; 如果a是负数则可能溢出），但是还是很容易出错。