## org.apache.taglibs.standard.lang.jstl
Class Coercions

    java.lang.Object
      org.apache.taglibs.standard.lang.jstl.Coercions

    public class Coercions

extends Object

This class contains the logic for coercing data types before operators are applied to them.

The following is the list of rules applied for various type conversions.

     Applying arithmetic operator
       Binary operator - A {+,-,*} B
         if A and B are null
           return 0
         if A or B is Float, Double, or String containing ".", "e", or "E"
           coerce both A and B to Double
           apply operator
         otherwise
           coerce both A and B to Long
           apply operator
         if operator results in exception (such as divide by 0), error

       Binary operator - A {/,div} B
         if A and B are null
           return 0
         otherwise
           coerce both A and B to Double
           apply operator
         if operator results in exception (such as divide by 0), error

       Binary operator - A {%,mod} B
         if A and B are null
           return 0
         if A or B is Float, Double, or String containing ".", "e" or "E"
           coerce both to Double
           apply operator
         otherwise
           coerce both A and B to Long
           apply operator
         if operator results in exception (such as divide by 0), error

       Unary minus operator - -A
         if A is null
           return 0
         if A is String
           if A contains ".", "e", or "E"
             coerce to Double, apply operator
           otherwise
             coerce to a Long and apply operator
         if A is Byte,Short,Integer,Long,Float,Double
           retain type, apply operator
         if operator results in exception, error
         otherwise
           error

     Applying "empty" operator - empty A
       if A is null
         return true
       if A is zero-length String
         return true
       if A is zero-length array
         return true
       if A is List and ((List) A).isEmpty()
         return true
       if A is Map and ((Map) A).isEmpty()
         return true
       otherwise
         return false

     Applying logical operators
       Binary operator - A {and,or} B
         coerce both A and B to Boolean, apply operator
       NOTE - operator stops as soon as expression can be determined, i.e.,
         A and B and C and D - if B is false, then only A and B is evaluated
       Unary not operator - not A
         coerce A to Boolean, apply operator

     Applying relational operator
       A {<,>,<=,>=,lt,gt,lte,gte} B
         if A==B
           if operator is >= or <=
             return true
           otherwise
             return false
         if A or B is null
           return false
         if A or B is Float or Double
           coerce both A and B to Double
           apply operator
         if A or B is Byte,Short,Character,Integer,Long
           coerce both A and B to Long
           apply operator
         if A or B is String
           coerce both A and B to String, compare lexically
         if A is Comparable
           if A.compareTo (B) throws exception
             error
           otherwise
             use result of A.compareTo(B)
         if B is Comparable
           if B.compareTo (A) throws exception
             error
           otherwise
             use result of B.compareTo(A)
         otherwise
           error

     Applying equality operator
       A {==,!=} B
         if A==B
           apply operator
         if A or B is null
           return false for ==, true for !=
         if A or B is Float or Double
           coerce both A and B to Double
           apply operator
         if A or B is Byte,Short,Character,Integer,Long
           coerce both A and B to Long
           apply operator
         if A or B is Boolean
           coerce both A and B to Boolean
           apply operator
         if A or B is String
           coerce both A and B to String, compare lexically
         otherwise
           if an error occurs while calling A.equals(B)
             error
           apply operator to result of A.equals(B)

     coercions

       coerce A to String
         A is String
           return A
         A is null
           return ""
         A.toString throws exception
           error
         otherwise
           return A.toString

       coerce A to primitive Number type N
         A is null or ""
           return 0
         A is Character
           convert to short, apply following rules
         A is Boolean
           error
         A is Number type N
           return A
         A is Number with less precision than N
           coerce quietly
         A is Number with greater precision than N
           coerce quietly
         A is String
           new N.valueOf(A) throws exception
             error
           return N.valueOf(A)
         otherwise
           error

       coerce A to Character should be
         A is null or ""
           return (char) 0
         A is Character
           return A
         A is Boolean
           error
         A is Number with less precision than short
           coerce quietly - return (char) A
         A is Number with greater precision than short
           coerce quietly - return (char) A
         A is String
           return A.charAt (0)
         otherwise
           error

       coerce A to Boolean
         A is null or ""
           return false
         A is Boolean
           return A
         A is String
           Boolean.valueOf(A) throws exception
             error
           return Boolean.valueOf(A)
         otherwise
           error

       coerce A to any other type T
         A is null
           return null
         A is assignable to T
           coerce quietly
         A is String
           T has no PropertyEditor
             if A is "", return null
             otherwise error
           T's PropertyEditor throws exception
             if A is "", return null
             otherwise error
           otherwise
             apply T's PropertyEditor
         otherwise
           error

Version:
  $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: tcfujii $
Author:
  Nathan Abramson - Art Technology Group

Constructor Summary
`Coercions()`

Method Summary
`static Object` `applyArithmeticOperator(Object pLeft, Object pRight, ArithmeticOperator pOperator, Logger pLogger)` Performs all of the necessary type conversions, then calls on the appropriate operator.
`static Object` `applyEqualityOperator(Object pLeft, Object pRight, EqualityOperator pOperator, Logger pLogger)` Performs all of the necessary type conversions, then calls on the appropriate operator.
`static Object` `applyRelationalOperator(Object pLeft, Object pRight, RelationalOperator pOperator, Logger pLogger)` Performs all of the necessary type conversions, then calls on the appropriate operator.
`static Object` `coerce(Object pValue, Class pClass, Logger pLogger)` Coerces the given value to the specified class.
`static Boolean` `coerceToBoolean(Object pValue, Logger pLogger)` Coerces a value to a Boolean
`static Character` `coerceToCharacter(Object pValue, Logger pLogger)` Coerces a value to a Character
`static Integer` `coerceToInteger(Object pValue, Logger pLogger)` Coerces a value to an Integer, returning null if the coercion isn't possible.
`static Object` `coerceToObject(Object pValue, Class pClass, Logger pLogger)` Coerces a value to the specified Class that is not covered by any of the above cases
`static Number` `coerceToPrimitiveNumber(Object pValue, Class pClass, Logger pLogger)` Coerces a value to the given primitive number class
`static String` `coerceToString(Object pValue, Logger pLogger)` Coerces the specified value to a String
`static boolean` `isFloatingPointString(Object pObject)` Returns true if the given string might contain a floating point number - i.e., it contains ".", "e", or "E"
`static boolean` `isFloatingPointType(Class pClass)` Returns true if the given class is of a floating point type
`static boolean` `isFloatingPointType(Object pObject)` Returns true if the given Object is of a floating point type
`static boolean` `isIntegerType(Class pClass)` Returns true if the given class is of an integer type
`static boolean` `isIntegerType(Object pObject)` Returns true if the given Object is of an integer type

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### Coercions

    public Coercions()

Method Detail

### coerce

    public static Object coerce(Object pValue,
                                Class pClass,
                                Logger pLogger)
                         throws ELException

  Coerces the given value to the specified class.

  Throws:
    `ELException`

### coerceToString

    public static String coerceToString(Object pValue,
                                        Logger pLogger)
                                 throws ELException

  Coerces the specified value to a String

  Throws:
    `ELException`

### coerceToPrimitiveNumber

    public static Number coerceToPrimitiveNumber(Object pValue,
                                                 Class pClass,
                                                 Logger pLogger)
                                          throws ELException

  Coerces a value to the given primitive number class

  Throws:
    `ELException`

### coerceToInteger

    public static Integer coerceToInteger(Object pValue,
                                          Logger pLogger)
                                   throws ELException

  Coerces a value to an Integer, returning null if the coercion isn't possible.

  Throws:
    `ELException`

### coerceToCharacter

    public static Character coerceToCharacter(Object pValue,
                                              Logger pLogger)
                                       throws ELException

  Coerces a value to a Character

  Throws:
    `ELException`

### coerceToBoolean

    public static Boolean coerceToBoolean(Object pValue,
                                          Logger pLogger)
                                   throws ELException

  Coerces a value to a Boolean

  Throws:
    `ELException`

### coerceToObject

    public static Object coerceToObject(Object pValue,
                                        Class pClass,
                                        Logger pLogger)
                                 throws ELException

  Coerces a value to the specified Class that is not covered by any of the above cases

  Throws:
    `ELException`

### applyArithmeticOperator

    public static Object applyArithmeticOperator(Object pLeft,
                                                 Object pRight,
                                                 ArithmeticOperator pOperator,
                                                 Logger pLogger)
                                          throws ELException

  Performs all of the necessary type conversions, then calls on the appropriate operator.

  Throws:
    `ELException`

### applyRelationalOperator

    public static Object applyRelationalOperator(Object pLeft,
                                                 Object pRight,
                                                 RelationalOperator pOperator,
                                                 Logger pLogger)
                                          throws ELException

  Performs all of the necessary type conversions, then calls on the appropriate operator.

  Throws:
    `ELException`

### applyEqualityOperator

    public static Object applyEqualityOperator(Object pLeft,
                                               Object pRight,
                                               EqualityOperator pOperator,
                                               Logger pLogger)
                                        throws ELException

  Performs all of the necessary type conversions, then calls on the appropriate operator.

  Throws:
    `ELException`

### isFloatingPointType

    public static boolean isFloatingPointType(Object pObject)

  Returns true if the given Object is of a floating point type

### isFloatingPointType

    public static boolean isFloatingPointType(Class pClass)

  Returns true if the given class is of a floating point type

### isFloatingPointString

    public static boolean isFloatingPointString(Object pObject)

  Returns true if the given string might contain a floating point number - i.e., it contains ".", "e", or "E"

### isIntegerType

    public static boolean isIntegerType(Object pObject)

  Returns true if the given Object is of an integer type

### isIntegerType

    public static boolean isIntegerType(Class pClass)

  Returns true if the given class is of an integer type

Copyright © 2008 Mort Bay Consulting. All Rights Reserved.