Class ELEvaluator
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- org.apache.taglibs.standard.lang.jstl.ELEvaluator
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public class ELEvaluator extends java.lang.Object
This is the main class for evaluating expression Strings. An expression String is a String that may contain expressions of the form ${...}. Multiple expressions may appear in the same expression String. In such a case, the expression String's value is computed by concatenating the String values of those evaluated expressions and any intervening non-expression text, then converting the resulting String to the expected type using the PropertyEditor mechanism.
In the special case where the expression String is a single expression, the value of the expression String is determined by evaluating the expression, without any intervening conversion to a String.
The evaluator maintains a cache mapping expression Strings to their parsed results. For expression Strings containing no expression elements, it maintains a cache mapping ExpectedType/ExpressionString to parsed value, so that static expression Strings won't have to go through a conversion step every time they are used. All instances of the evaluator share the same cache. The cache may be bypassed by setting a flag on the evaluator's constructor.
The evaluator must be passed a VariableResolver in its constructor. The VariableResolver is used to resolve variable names encountered in expressions, and can also be used to implement "implicit objects" that are always present in the namespace. Different applications will have different policies for variable lookups and implicit objects - these differences can be encapsulated in the VariableResolver passed to the evaluator's constructor.
Most VariableResolvers will need to perform their resolution against some context. For example, a JSP environment needs a PageContext to resolve variables. The evaluate() method takes a generic Object context which is eventually passed to the VariableResolver - the VariableResolver is responsible for casting the context to the proper type.
Once an evaluator instance has been constructed, it may be used multiple times, and may be used by multiple simultaneous Threads. In other words, an evaluator instance is well-suited for use as a singleton.
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Field Summary
Fields Modifier and Type Field Description private static java.lang.String
EXPR_CACHE_PARAM
Name of configuration setting for maximum number of entries in the cached expression string mapprivate static int
MAX_SIZE
Default maximum cache size(package private) boolean
mBypassCache
Flag if the cache should be bypassed *(package private) VariableResolver
mResolver
The VariableResolver *(package private) javax.servlet.jsp.PageContext
pageContext
The PageContext *(package private) static java.util.Map
sCachedExpectedTypes
The mapping from ExpectedType to Maps mapping literal String to parsed value *(package private) static java.util.Map
sCachedExpressionStrings
The mapping from expression String to its parsed form (String, Expression, or ExpressionString)(package private) static Logger
sLogger
The static Logger *
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Constructor Summary
Constructors Constructor Description ELEvaluator(VariableResolver pResolver)
Constructor
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description (package private) static java.lang.String
addEscapes(java.lang.String str)
Used to convert raw characters to their escaped version when these raw version cannot be used as part of an ASCII string literal.(package private) java.lang.Object
convertStaticValueToExpectedType(java.lang.String pValue, java.lang.Class pExpectedType, Logger pLogger)
Converts the given String, specified as a static expression string, to the given expected type.(package private) java.lang.Object
convertToExpectedType(java.lang.Object pValue, java.lang.Class pExpectedType, Logger pLogger)
Converts the given value to the specified expected type.private void
createExpressionStringMap()
Creates LRU map of expression strings.java.lang.Object
evaluate(java.lang.String pExpressionString, java.lang.Object pContext, java.lang.Class pExpectedType, java.util.Map functions, java.lang.String defaultPrefix)
Evaluates the given expression String(package private) java.lang.Object
evaluate(java.lang.String pExpressionString, java.lang.Object pContext, java.lang.Class pExpectedType, java.util.Map functions, java.lang.String defaultPrefix, Logger pLogger)
Evaluates the given expression string(package private) static java.lang.String
formatParseException(java.lang.String pExpressionString, ParseException pExc)
Formats a ParseException into an error message suitable for displaying on a web page(package private) static java.util.Map
getOrCreateExpectedTypeMap(java.lang.Class pExpectedType)
Creates or returns the Map that maps string literals to parsed values for the specified expected type.java.lang.String
parseAndRender(java.lang.String pExpressionString)
Parses the given expression string, then converts it back to a String in its canonical form.java.lang.Object
parseExpressionString(java.lang.String pExpressionString)
Gets the parsed form of the given expression string.void
setBypassCache(boolean pBypassCache)
Enable cache bypass
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Field Detail
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EXPR_CACHE_PARAM
private static final java.lang.String EXPR_CACHE_PARAM
Name of configuration setting for maximum number of entries in the cached expression string map- See Also:
- Constant Field Values
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MAX_SIZE
private static final int MAX_SIZE
Default maximum cache size- See Also:
- Constant Field Values
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sCachedExpressionStrings
static java.util.Map sCachedExpressionStrings
The mapping from expression String to its parsed form (String, Expression, or ExpressionString)Using LRU Map with a maximum capacity to avoid out of bound map growth.
NOTE: use LinkedHashmap if a dependency on J2SE 1.4+ is ok
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sCachedExpectedTypes
static java.util.Map sCachedExpectedTypes
The mapping from ExpectedType to Maps mapping literal String to parsed value *
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sLogger
static Logger sLogger
The static Logger *
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mResolver
VariableResolver mResolver
The VariableResolver *
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mBypassCache
boolean mBypassCache
Flag if the cache should be bypassed *
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pageContext
javax.servlet.jsp.PageContext pageContext
The PageContext *
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Constructor Detail
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ELEvaluator
public ELEvaluator(VariableResolver pResolver)
Constructor- Parameters:
pResolver
- the object that should be used to resolve variable names encountered in expressions. If null, all variable references will resolve to null.
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Method Detail
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setBypassCache
public void setBypassCache(boolean pBypassCache)
Enable cache bypass- Parameters:
pBypassCache
- flag indicating cache should be bypassed
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evaluate
public java.lang.Object evaluate(java.lang.String pExpressionString, java.lang.Object pContext, java.lang.Class pExpectedType, java.util.Map functions, java.lang.String defaultPrefix) throws ELException
Evaluates the given expression String- Parameters:
pExpressionString
- the expression String to be evaluatedpContext
- the context passed to the VariableResolver for resolving variable namespExpectedType
- the type to which the evaluated expression should be coerced- Returns:
- the expression String evaluated to the given expected type
- Throws:
ELException
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evaluate
java.lang.Object evaluate(java.lang.String pExpressionString, java.lang.Object pContext, java.lang.Class pExpectedType, java.util.Map functions, java.lang.String defaultPrefix, Logger pLogger) throws ELException
Evaluates the given expression string- Throws:
ELException
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parseExpressionString
public java.lang.Object parseExpressionString(java.lang.String pExpressionString) throws ELException
Gets the parsed form of the given expression string. If the parsed form is cached (and caching is not bypassed), return the cached form, otherwise parse and cache the value. Returns either a String, Expression, or ExpressionString.- Throws:
ELException
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convertToExpectedType
java.lang.Object convertToExpectedType(java.lang.Object pValue, java.lang.Class pExpectedType, Logger pLogger) throws ELException
Converts the given value to the specified expected type.- Throws:
ELException
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convertStaticValueToExpectedType
java.lang.Object convertStaticValueToExpectedType(java.lang.String pValue, java.lang.Class pExpectedType, Logger pLogger) throws ELException
Converts the given String, specified as a static expression string, to the given expected type. The conversion is cached.- Throws:
ELException
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getOrCreateExpectedTypeMap
static java.util.Map getOrCreateExpectedTypeMap(java.lang.Class pExpectedType)
Creates or returns the Map that maps string literals to parsed values for the specified expected type.
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createExpressionStringMap
private void createExpressionStringMap()
Creates LRU map of expression strings. If context parameter specifying cache size is present use that as the maximum size of the LRU map otherwise use default.
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formatParseException
static java.lang.String formatParseException(java.lang.String pExpressionString, ParseException pExc)
Formats a ParseException into an error message suitable for displaying on a web page
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addEscapes
static java.lang.String addEscapes(java.lang.String str)
Used to convert raw characters to their escaped version when these raw version cannot be used as part of an ASCII string literal.
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parseAndRender
public java.lang.String parseAndRender(java.lang.String pExpressionString) throws ELException
Parses the given expression string, then converts it back to a String in its canonical form. This is used to test parsing.- Throws:
ELException
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