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Jexl is an implementation of the JSTL Expression Language with extensions.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.jexl2;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import org.apache.commons.jexl2.introspection.JexlMethod;
import org.apache.commons.jexl2.introspection.Uberspect;
import org.apache.commons.jexl2.parser.ASTJexlScript;
import org.apache.commons.jexl2.parser.JexlNode;
import org.apache.commons.jexl2.parser.StringParser;
/**
* An evaluator similar to the Unified EL evaluator used in JSP/JSF based on JEXL.
* It is intended to be used in configuration modules, XML based frameworks or JSP taglibs
* and facilitate the implementation of expression evaluation.
*
* An expression can mix immediate, deferred and nested sub-expressions as well as string constants;
*
* - The "immediate" syntax is of the form
"...${jexl-expr}..."
* - The "deferred" syntax is of the form
"...#{jexl-expr}..."
* - The "nested" syntax is of the form
"...#{...${jexl-expr0}...}..."
* - The "composite" syntax is of the form
"...${jexl-expr0}... #{jexl-expr1}..."
*
*
*
* Deferred & immediate expression carry different intentions:
*
* - An immediate expression indicate that evaluation is intended to be performed close to
* the definition/parsing point.
* - A deferred expression indicate that evaluation is intended to occur at a later stage.
*
*
*
* For instance: "Hello ${name}, now is #{time}" is a composite "deferred" expression since one
* of its subexpressions is deferred. Furthermore, this (composite) expression intent is
* to perform two evaluations; one close to its definition and another one in a later
* phase.
*
*
* The API reflects this feature in 2 methods, prepare and evaluate. The prepare method
* will evaluate the immediate subexpression and return an expression that contains only
* the deferred subexpressions (& constants), a prepared expression. Such a prepared expression
* is suitable for a later phase evaluation that may occur with a different JexlContext.
* Note that it is valid to call evaluate without prepare in which case the same JexlContext
* is used for the 2 evaluation phases.
*
*
* In the most common use-case where deferred expressions are to be kept around as properties of objects,
* one should parse & prepare an expression before storing it and evaluate it each time
* the property storing it is accessed.
*
*
* Note that nested expression use the JEXL syntax as in:
* "#{${bar}+'.charAt(2)'}"
* The most common mistake leading to an invalid expression being the following:
* "#{${bar}charAt(2)}"
*
* Also note that methods that parse evaluate expressions may throw unchecked exceptions;
* The {@link UnifiedJEXL.Exception} are thrown when the engine instance is in "non-silent" mode
* but since these are RuntimeException, user-code should catch them where appropriate.
*
* @since 2.0
*/
public final class UnifiedJEXL {
/** The JEXL engine instance. */
private final JexlEngine jexl;
/** The expression cache. */
private final JexlEngine.SoftCache cache;
/** The default cache size. */
private static final int CACHE_SIZE = 256;
/** The first character for immediate expressions. */
private static final char IMM_CHAR = '$';
/** The first character for deferred expressions. */
private static final char DEF_CHAR = '#';
/**
* Creates a new instance of UnifiedJEXL with a default size cache.
* @param aJexl the JexlEngine to use.
*/
public UnifiedJEXL(JexlEngine aJexl) {
this(aJexl, CACHE_SIZE);
}
/**
* Creates a new instance of UnifiedJEXL creating a local cache.
* @param aJexl the JexlEngine to use.
* @param cacheSize the number of expressions in this cache
*/
public UnifiedJEXL(JexlEngine aJexl, int cacheSize) {
this.jexl = aJexl;
this.cache = aJexl.new SoftCache(cacheSize);
}
/**
* Types of expressions.
* Each instance carries a counter index per (composite sub-) expression type.
* @see ExpressionBuilder
*/
private static enum ExpressionType {
/** Constant expression, count index 0. */
CONSTANT(0),
/** Immediate expression, count index 1. */
IMMEDIATE(1),
/** Deferred expression, count index 2. */
DEFERRED(2),
/** Nested (which are deferred) expressions, count index 2. */
NESTED(2),
/** Composite expressions are not counted, index -1. */
COMPOSITE(-1);
/** The index in arrays of expression counters for composite expressions. */
private final int index;
/**
* Creates an ExpressionType.
* @param idx the index for this type in counters arrays.
*/
ExpressionType(int idx) {
this.index = idx;
}
}
/**
* A helper class to build expressions.
* Keeps count of sub-expressions by type.
*/
private static class ExpressionBuilder {
/** Per expression type counters. */
private final int[] counts;
/** The list of expressions. */
private final ArrayList expressions;
/**
* Creates a builder.
* @param size the initial expression array size
*/
ExpressionBuilder(int size) {
counts = new int[]{0, 0, 0};
expressions = new ArrayList(size <= 0 ? 3 : size);
}
/**
* Adds an expression to the list of expressions, maintain per-type counts.
* @param expr the expression to add
*/
void add(Expression expr) {
counts[expr.getType().index] += 1;
expressions.add(expr);
}
/**
* Builds an expression from a source, performs checks.
* @param el the unified el instance
* @param source the source expression
* @return an expression
*/
Expression build(UnifiedJEXL el, Expression source) {
int sum = 0;
for (int count : counts) {
sum += count;
}
if (expressions.size() != sum) {
StringBuilder error = new StringBuilder("parsing algorithm error, exprs: ");
error.append(expressions.size());
error.append(", constant:");
error.append(counts[ExpressionType.CONSTANT.index]);
error.append(", immediate:");
error.append(counts[ExpressionType.IMMEDIATE.index]);
error.append(", deferred:");
error.append(counts[ExpressionType.DEFERRED.index]);
throw new IllegalStateException(error.toString());
}
// if only one sub-expr, no need to create a composite
if (expressions.size() == 1) {
return expressions.get(0);
} else {
return el.new CompositeExpression(counts, expressions, source);
}
}
}
/**
* Gets the JexlEngine underlying the UnifiedJEXL.
* @return the JexlEngine
*/
public JexlEngine getEngine() {
return jexl;
}
/**
* Clears the cache.
* @since 2.1
*/
public void clearCache() {
synchronized (cache) {
cache.clear();
}
}
/**
* The sole type of (runtime) exception the UnifiedJEXL can throw.
*/
public static class Exception extends RuntimeException {
/** Serial version UID. */
private static final long serialVersionUID = -8201402995815975726L;
/**
* Creates a UnifiedJEXL.Exception.
* @param msg the exception message
* @param cause the exception cause
*/
public Exception(String msg, Throwable cause) {
super(msg, cause);
}
}
/**
* The abstract base class for all expressions, immediate '${...}' and deferred '#{...}'.
*/
public abstract class Expression {
/** The source of this expression (see {@link UnifiedJEXL.Expression#prepare}). */
protected final Expression source;
/**
* Creates an expression.
* @param src the source expression if any
*/
Expression(Expression src) {
this.source = src != null ? src : this;
}
/**
* Checks whether this expression is immediate.
* @return true if immediate, false otherwise
*/
public boolean isImmediate() {
return true;
}
/**
* Checks whether this expression is deferred.
* @return true if deferred, false otherwise
*/
public final boolean isDeferred() {
return !isImmediate();
}
/**
* Gets this expression type.
* @return its type
*/
abstract ExpressionType getType();
/**
* Formats this expression, adding its source string representation in
* comments if available: 'expression /*= source *\/'' .
* Note: do not override; will be made final in a future release.
* @return the formatted expression string
*/
@Override
public String toString() {
StringBuilder strb = new StringBuilder();
asString(strb);
if (source != this) {
strb.append(" /*= ");
strb.append(source.toString());
strb.append(" */");
}
return strb.toString();
}
/**
* Generates this expression's string representation.
* @return the string representation
*/
public String asString() {
StringBuilder strb = new StringBuilder();
asString(strb);
return strb.toString();
}
/**
* Adds this expression's string representation to a StringBuilder.
* @param strb the builder to fill
* @return the builder argument
*/
public abstract StringBuilder asString(StringBuilder strb);
/**
* Gets the list of variables accessed by this expression.
* This method will visit all nodes of the sub-expressions and extract all variables whether they
* are written in 'dot' or 'bracketed' notation. (a.b is equivalent to a['b']).
* @return the set of variables, each as a list of strings (ant-ish variables use more than 1 string)
* or the empty set if no variables are used
* @since 2.1
*/
public Set> getVariables() {
return Collections.emptySet();
}
/**
* Fills up the list of variables accessed by this expression.
* @param refs the set of variable being filled
* @since 2.1
*/
protected void getVariables(Set> refs) {
// nothing to do
}
/**
* Evaluates the immediate sub-expressions.
*
* When the expression is dependant upon immediate and deferred sub-expressions,
* evaluates the immediate sub-expressions with the context passed as parameter
* and returns this expression deferred form.
*
*
* In effect, this binds the result of the immediate sub-expressions evaluation in the
* context, allowing to differ evaluation of the remaining (deferred) expression within another context.
* This only has an effect to nested & composite expressions that contain differed & immediate sub-expressions.
*
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warning.
*
* Note: do not override; will be made final in a future release.
* @param context the context to use for immediate expression evaluations
* @return an expression or null if an error occurs and the {@link JexlEngine} is running in silent mode
* @throws UnifiedJEXL.Exception if an error occurs and the {@link JexlEngine} is not in silent mode
*/
public Expression prepare(JexlContext context) {
try {
Interpreter interpreter = new Interpreter(jexl, context, !jexl.isLenient(), jexl.isSilent());
if (context instanceof TemplateContext) {
interpreter.setFrame(((TemplateContext) context).getFrame());
}
return prepare(interpreter);
} catch (JexlException xjexl) {
Exception xuel = createException("prepare", this, xjexl);
if (jexl.isSilent()) {
jexl.logger.warn(xuel.getMessage(), xuel.getCause());
return null;
}
throw xuel;
}
}
/**
* Evaluates this expression.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warning.
*
* Note: do not override; will be made final in a future release.
* @param context the variable context
* @return the result of this expression evaluation or null if an error occurs and the {@link JexlEngine} is
* running in silent mode
* @throws UnifiedJEXL.Exception if an error occurs and the {@link JexlEngine} is not silent
*/
public Object evaluate(JexlContext context) {
try {
Interpreter interpreter = new Interpreter(jexl, context, !jexl.isLenient(), jexl.isSilent());
if (context instanceof TemplateContext) {
interpreter.setFrame(((TemplateContext) context).getFrame());
}
return evaluate(interpreter);
} catch (JexlException xjexl) {
Exception xuel = createException("prepare", this, xjexl);
if (jexl.isSilent()) {
jexl.logger.warn(xuel.getMessage(), xuel.getCause());
return null;
}
throw xuel;
}
}
/**
* Retrieves this expression's source expression.
* If this expression was prepared, this allows to retrieve the
* original expression that lead to it.
* Other expressions return themselves.
* @return the source expression
*/
public final Expression getSource() {
return source;
}
/**
* Prepares a sub-expression for interpretation.
* @param interpreter a JEXL interpreter
* @return a prepared expression
* @throws JexlException (only for nested & composite)
*/
protected Expression prepare(Interpreter interpreter) {
return this;
}
/**
* Intreprets a sub-expression.
* @param interpreter a JEXL interpreter
* @return the result of interpretation
* @throws JexlException (only for nested & composite)
*/
protected abstract Object evaluate(Interpreter interpreter);
}
/** A constant expression. */
private class ConstantExpression extends Expression {
/** The constant held by this expression. */
private final Object value;
/**
* Creates a constant expression.
*
* If the wrapped constant is a string, it is treated
* as a JEXL strings with respect to escaping.
*
* @param val the constant value
* @param source the source expression if any
*/
ConstantExpression(Object val, Expression source) {
super(source);
if (val == null) {
throw new NullPointerException("constant can not be null");
}
if (val instanceof String) {
val = StringParser.buildString((String) val, false);
}
this.value = val;
}
/** {@inheritDoc} */
@Override
ExpressionType getType() {
return ExpressionType.CONSTANT;
}
/** {@inheritDoc} */
@Override
public StringBuilder asString(StringBuilder strb) {
if (value != null) {
strb.append(value.toString());
}
return strb;
}
/** {@inheritDoc} */
@Override
protected Object evaluate(Interpreter interpreter) {
return value;
}
}
/** The base for Jexl based expressions. */
private abstract class JexlBasedExpression extends Expression {
/** The JEXL string for this expression. */
protected final CharSequence expr;
/** The JEXL node for this expression. */
protected final JexlNode node;
/**
* Creates a JEXL interpretable expression.
* @param theExpr the expression as a string
* @param theNode the expression as an AST
* @param theSource the source expression if any
*/
protected JexlBasedExpression(CharSequence theExpr, JexlNode theNode, Expression theSource) {
super(theSource);
this.expr = theExpr;
this.node = theNode;
}
/** {@inheritDoc} */
@Override
public StringBuilder asString(StringBuilder strb) {
strb.append(isImmediate() ? IMM_CHAR : DEF_CHAR);
strb.append("{");
strb.append(expr);
strb.append("}");
return strb;
}
/** {@inheritDoc} */
@Override
protected Object evaluate(Interpreter interpreter) {
return interpreter.interpret(node);
}
/** {@inheritDoc} */
@Override
public Set> getVariables() {
Set> refs = new LinkedHashSet>();
getVariables(refs);
return refs;
}
/** {@inheritDoc} */
@Override
protected void getVariables(Set> refs) {
jexl.getVariables(node, refs, null);
}
}
/** An immediate expression: ${jexl}. */
private class ImmediateExpression extends JexlBasedExpression {
/**
* Creates an immediate expression.
* @param expr the expression as a string
* @param node the expression as an AST
* @param source the source expression if any
*/
ImmediateExpression(CharSequence expr, JexlNode node, Expression source) {
super(expr, node, source);
}
/** {@inheritDoc} */
@Override
ExpressionType getType() {
return ExpressionType.IMMEDIATE;
}
/** {@inheritDoc} */
@Override
protected Expression prepare(Interpreter interpreter) {
// evaluate immediate as constant
Object value = evaluate(interpreter);
return value != null ? new ConstantExpression(value, source) : null;
}
}
/** A deferred expression: #{jexl}. */
private class DeferredExpression extends JexlBasedExpression {
/**
* Creates a deferred expression.
* @param expr the expression as a string
* @param node the expression as an AST
* @param source the source expression if any
*/
DeferredExpression(CharSequence expr, JexlNode node, Expression source) {
super(expr, node, source);
}
/** {@inheritDoc} */
@Override
public boolean isImmediate() {
return false;
}
/** {@inheritDoc} */
@Override
ExpressionType getType() {
return ExpressionType.DEFERRED;
}
/** {@inheritDoc} */
@Override
protected Expression prepare(Interpreter interpreter) {
return new ImmediateExpression(expr, node, source);
}
/** {@inheritDoc} */
@Override
protected void getVariables(Set> refs) {
// noop
}
}
/**
* An immediate expression nested into a deferred expression.
* #{...${jexl}...}
* Note that the deferred syntax is JEXL's, not UnifiedJEXL.
*/
private class NestedExpression extends JexlBasedExpression {
/**
* Creates a nested expression.
* @param expr the expression as a string
* @param node the expression as an AST
* @param source the source expression if any
*/
NestedExpression(CharSequence expr, JexlNode node, Expression source) {
super(expr, node, source);
if (this.source != this) {
throw new IllegalArgumentException("Nested expression can not have a source");
}
}
@Override
public StringBuilder asString(StringBuilder strb) {
strb.append(expr);
return strb;
}
/** {@inheritDoc} */
@Override
public boolean isImmediate() {
return false;
}
/** {@inheritDoc} */
@Override
ExpressionType getType() {
return ExpressionType.NESTED;
}
/** {@inheritDoc} */
@Override
protected Expression prepare(Interpreter interpreter) {
String value = interpreter.interpret(node).toString();
JexlNode dnode = jexl.parse(value, jexl.isDebug() ? node.debugInfo() : null, null);
return new ImmediateExpression(value, dnode, this);
}
/** {@inheritDoc} */
@Override
protected Object evaluate(Interpreter interpreter) {
return prepare(interpreter).evaluate(interpreter);
}
}
/** A composite expression: "... ${...} ... #{...} ...". */
private class CompositeExpression extends Expression {
/** Bit encoded (deferred count > 0) bit 1, (immediate count > 0) bit 0. */
private final int meta;
/** The list of sub-expression resulting from parsing. */
protected final Expression[] exprs;
/**
* Creates a composite expression.
* @param counters counters of expression per type
* @param list the sub-expressions
* @param src the source for this expresion if any
*/
CompositeExpression(int[] counters, ArrayList list, Expression src) {
super(src);
this.exprs = list.toArray(new Expression[list.size()]);
this.meta = (counters[ExpressionType.DEFERRED.index] > 0 ? 2 : 0)
| (counters[ExpressionType.IMMEDIATE.index] > 0 ? 1 : 0);
}
/** {@inheritDoc} */
@Override
public boolean isImmediate() {
// immediate if no deferred
return (meta & 2) == 0;
}
/** {@inheritDoc} */
@Override
ExpressionType getType() {
return ExpressionType.COMPOSITE;
}
/** {@inheritDoc} */
@Override
public StringBuilder asString(StringBuilder strb) {
for (Expression e : exprs) {
e.asString(strb);
}
return strb;
}
/** {@inheritDoc} */
@Override
public Set> getVariables() {
Set> refs = new LinkedHashSet>();
for (Expression expr : exprs) {
expr.getVariables(refs);
}
return refs;
}
/** {@inheritDoc} */
@Override
protected Expression prepare(Interpreter interpreter) {
// if this composite is not its own source, it is already prepared
if (source != this) {
return this;
}
// we need to prepare all sub-expressions
final int size = exprs.length;
final ExpressionBuilder builder = new ExpressionBuilder(size);
// tracking whether prepare will return a different expression
boolean eq = true;
for (int e = 0; e < size; ++e) {
Expression expr = exprs[e];
Expression prepared = expr.prepare(interpreter);
// add it if not null
if (prepared != null) {
builder.add(prepared);
}
// keep track of expression equivalence
eq &= expr == prepared;
}
Expression ready = eq ? this : builder.build(UnifiedJEXL.this, this);
return ready;
}
/** {@inheritDoc} */
@Override
protected Object evaluate(Interpreter interpreter) {
final int size = exprs.length;
Object value = null;
// common case: evaluate all expressions & concatenate them as a string
StringBuilder strb = new StringBuilder();
for (int e = 0; e < size; ++e) {
value = exprs[e].evaluate(interpreter);
if (value != null) {
strb.append(value.toString());
}
}
value = strb.toString();
return value;
}
}
/** Creates a a {@link UnifiedJEXL.Expression} from an expression string.
* Uses & fills up the expression cache if any.
*
* If the underlying JEXL engine is silent, errors will be logged through its logger as warnings.
*
* @param expression the UnifiedJEXL string expression
* @return the UnifiedJEXL object expression, null if silent and an error occured
* @throws UnifiedJEXL.Exception if an error occurs and the {@link JexlEngine} is not silent
*/
public Expression parse(String expression) {
Exception xuel = null;
Expression stmt = null;
try {
if (cache == null) {
stmt = parseExpression(expression, null);
} else {
synchronized (cache) {
stmt = cache.get(expression);
if (stmt == null) {
stmt = parseExpression(expression, null);
cache.put(expression, stmt);
}
}
}
} catch (JexlException xjexl) {
xuel = new Exception("failed to parse '" + expression + "'", xjexl);
} catch (Exception xany) {
xuel = xany;
} finally {
if (xuel != null) {
if (jexl.isSilent()) {
jexl.logger.warn(xuel.getMessage(), xuel.getCause());
return null;
}
throw xuel;
}
}
return stmt;
}
/**
* Creates a UnifiedJEXL.Exception from a JexlException.
* @param action parse, prepare, evaluate
* @param expr the expression
* @param xany the exception
* @return an exception containing an explicit error message
*/
private Exception createException(String action, Expression expr, java.lang.Exception xany) {
StringBuilder strb = new StringBuilder("failed to ");
strb.append(action);
if (expr != null) {
strb.append(" '");
strb.append(expr.toString());
strb.append("'");
}
Throwable cause = xany.getCause();
if (cause != null) {
String causeMsg = cause.getMessage();
if (causeMsg != null) {
strb.append(", ");
strb.append(causeMsg);
}
}
return new Exception(strb.toString(), xany);
}
/** The different parsing states. */
private static enum ParseState {
/** Parsing a constant. */
CONST,
/** Parsing after $ .*/
IMMEDIATE0,
/** Parsing after # .*/
DEFERRED0,
/** Parsing after ${ .*/
IMMEDIATE1,
/** Parsing after #{ .*/
DEFERRED1,
/** Parsing after \ .*/
ESCAPE
}
/**
* Parses a unified expression.
* @param expr the string expression
* @param scope the expression scope
* @return the expression instance
* @throws JexlException if an error occur during parsing
*/
private Expression parseExpression(String expr, JexlEngine.Scope scope) {
final int size = expr.length();
ExpressionBuilder builder = new ExpressionBuilder(0);
StringBuilder strb = new StringBuilder(size);
ParseState state = ParseState.CONST;
int inner = 0;
boolean nested = false;
int inested = -1;
for (int i = 0; i < size; ++i) {
char c = expr.charAt(i);
switch (state) {
default: // in case we ever add new expression type
throw new UnsupportedOperationException("unexpected expression type");
case CONST:
if (c == IMM_CHAR) {
state = ParseState.IMMEDIATE0;
} else if (c == DEF_CHAR) {
inested = i;
state = ParseState.DEFERRED0;
} else if (c == '\\') {
state = ParseState.ESCAPE;
} else {
// do buildup expr
strb.append(c);
}
break;
case IMMEDIATE0: // $
if (c == '{') {
state = ParseState.IMMEDIATE1;
// if chars in buffer, create constant
if (strb.length() > 0) {
Expression cexpr = new ConstantExpression(strb.toString(), null);
builder.add(cexpr);
strb.delete(0, Integer.MAX_VALUE);
}
} else {
// revert to CONST
strb.append(IMM_CHAR);
strb.append(c);
state = ParseState.CONST;
}
break;
case DEFERRED0: // #
if (c == '{') {
state = ParseState.DEFERRED1;
// if chars in buffer, create constant
if (strb.length() > 0) {
Expression cexpr = new ConstantExpression(strb.toString(), null);
builder.add(cexpr);
strb.delete(0, Integer.MAX_VALUE);
}
} else {
// revert to CONST
strb.append(DEF_CHAR);
strb.append(c);
state = ParseState.CONST;
}
break;
case IMMEDIATE1: // ${...
if (c == '}') {
// materialize the immediate expr
Expression iexpr = new ImmediateExpression(
strb.toString(),
jexl.parse(strb, null, scope),
null);
builder.add(iexpr);
strb.delete(0, Integer.MAX_VALUE);
state = ParseState.CONST;
} else {
// do buildup expr
strb.append(c);
}
break;
case DEFERRED1: // #{...
// skip inner strings (for '}')
if (c == '"' || c == '\'') {
strb.append(c);
i = StringParser.readString(strb, expr, i + 1, c);
continue;
}
// nested immediate in deferred; need to balance count of '{' & '}'
if (c == '{') {
if (expr.charAt(i - 1) == IMM_CHAR) {
inner += 1;
strb.deleteCharAt(strb.length() - 1);
nested = true;
}
continue;
}
// closing '}'
if (c == '}') {
// balance nested immediate
if (inner > 0) {
inner -= 1;
} else {
// materialize the nested/deferred expr
Expression dexpr = null;
if (nested) {
dexpr = new NestedExpression(
expr.substring(inested, i + 1),
jexl.parse(strb, null, scope),
null);
} else {
dexpr = new DeferredExpression(
strb.toString(),
jexl.parse(strb, null, scope),
null);
}
builder.add(dexpr);
strb.delete(0, Integer.MAX_VALUE);
nested = false;
state = ParseState.CONST;
}
} else {
// do buildup expr
strb.append(c);
}
break;
case ESCAPE:
if (c == DEF_CHAR) {
strb.append(DEF_CHAR);
} else if (c == IMM_CHAR) {
strb.append(IMM_CHAR);
} else {
strb.append('\\');
strb.append(c);
}
state = ParseState.CONST;
}
}
// we should be in that state
if (state != ParseState.CONST) {
throw new Exception("malformed expression: " + expr, null);
}
// if any chars were buffered, add them as a constant
if (strb.length() > 0) {
Expression cexpr = new ConstantExpression(strb.toString(), null);
builder.add(cexpr);
}
return builder.build(this, null);
}
/**
* The enum capturing the difference between verbatim and code source fragments.
*/
private static enum BlockType {
/** Block is to be output "as is". */
VERBATIM,
/** Block is a directive, ie a fragment of code. */
DIRECTIVE;
}
/**
* Abstract the source fragments, verbatim or immediate typed text blocks.
* @since 2.1
*/
private static final class TemplateBlock {
/** The type of block, verbatim or directive. */
private final BlockType type;
/** The actual contexnt. */
private final String body;
/**
* Creates a new block.
* @param theType the type
* @param theBlock the content
*/
TemplateBlock(BlockType theType, String theBlock) {
type = theType;
body = theBlock;
}
@Override
public String toString() {
return body;
}
}
/**
* A Template is a script that evaluates by writing its content through a Writer.
* This is a simplified replacement for Velocity that uses JEXL (instead of OGNL/VTL) as the scripting
* language.
*
* The source text is parsed considering each line beginning with '$$' (as default pattern) as JEXL script code
* and all others as Unified JEXL expressions; those expressions will be invoked from the script during
* evaluation and their output gathered through a writer.
* It is thus possible to use looping or conditional construct "around" expressions generating output.
*
* For instance:
*
* $$ for(var x : [1, 3, 5, 42, 169]) {
* $$ if (x == 42) {
* Life, the universe, and everything
* $$ } else if (x > 42) {
* The value $(x} is over fourty-two
* $$ } else {
* The value ${x} is under fourty-two
* $$ }
* $$ }
*
* Will evaluate as:
*
* The value 1 is under fourty-two
* The value 3 is under fourty-two
* The value 5 is under fourty-two
* Life, the universe, and everything
* The value 169 is over fourty-two
*
*
* During evaluation, the template context exposes its writer as '$jexl' which is safe to use in this case.
* This allows writing directly through the writer without adding new-lines as in:
*
* $$ for(var cell : cells) { $jexl.print(cell); $jexl.print(';') }
*
*
*
* A template is expanded as one JEXL script and a list of UnifiedJEXL expressions; each UnifiedJEXL expression
* being replace in the script by a call to jexl:print(expr) (the expr is in fact the expr number in the template).
* This integration uses a specialized JexlContext (TemplateContext) that serves as a namespace (for jexl:)
* and stores the expression array and the writer (java.io.Writer) that the 'jexl:print(...)'
* delegates the output generation to.
*
* @since 2.1
*/
public final class Template {
/** The prefix marker. */
private final String prefix;
/** The array of source blocks. */
private final TemplateBlock[] source;
/** The resulting script. */
private final ASTJexlScript script;
/** The UnifiedJEXL expressions called by the script. */
private final Expression[] exprs;
/**
* Creates a new template from an input.
* @param directive the prefix for lines of code; can not be "$", "${", "#" or "#{"
* since this would preclude being able to differentiate directives and UnifiedJEXL expressions
* @param reader the input reader
* @param parms the parameter names
* @throws NullPointerException if either the directive prefix or input is null
* @throws IllegalArgumentException if the directive prefix is invalid
*/
public Template(String directive, Reader reader, String... parms) {
if (directive == null) {
throw new NullPointerException("null prefix");
}
if ("$".equals(directive)
|| "${".equals(directive)
|| "#".equals(directive)
|| "#{".equals(directive)) {
throw new IllegalArgumentException(directive + ": is not a valid directive pattern");
}
if (reader == null) {
throw new NullPointerException("null input");
}
JexlEngine.Scope scope = new JexlEngine.Scope(parms);
prefix = directive;
List blocks = readTemplate(prefix, reader);
List uexprs = new ArrayList();
StringBuilder strb = new StringBuilder();
int nuexpr = 0;
int codeStart = -1;
for (int b = 0; b < blocks.size(); ++b) {
TemplateBlock block = blocks.get(b);
if (block.type == BlockType.VERBATIM) {
strb.append("jexl:print(");
strb.append(nuexpr++);
strb.append(");");
} else {
// keep track of first block of code, the frame creator
if (codeStart < 0) {
codeStart = b;
}
strb.append(block.body);
}
}
// parse the script
script = getEngine().parse(strb.toString(), null, scope);
scope = script.getScope();
// parse the exprs using the code frame for those appearing after the first block of code
for (int b = 0; b < blocks.size(); ++b) {
TemplateBlock block = blocks.get(b);
if (block.type == BlockType.VERBATIM) {
uexprs.add(UnifiedJEXL.this.parseExpression(block.body, b > codeStart ? scope : null));
}
}
source = blocks.toArray(new TemplateBlock[blocks.size()]);
exprs = uexprs.toArray(new Expression[uexprs.size()]);
}
/**
* Private ctor used to expand deferred expressions during prepare.
* @param thePrefix the directive prefix
* @param theSource the source
* @param theScript the script
* @param theExprs the expressions
*/
private Template(String thePrefix, TemplateBlock[] theSource, ASTJexlScript theScript, Expression[] theExprs) {
prefix = thePrefix;
source = theSource;
script = theScript;
exprs = theExprs;
}
@Override
public String toString() {
StringBuilder strb = new StringBuilder();
for (TemplateBlock block : source) {
if (block.type == BlockType.DIRECTIVE) {
strb.append(prefix);
}
strb.append(block.toString());
strb.append('\n');
}
return strb.toString();
}
/**
* Recreate the template source from its inner components.
* @return the template source rewritten
*/
public String asString() {
StringBuilder strb = new StringBuilder();
int e = 0;
for (int b = 0; b < source.length; ++b) {
TemplateBlock block = source[b];
if (block.type == BlockType.DIRECTIVE) {
strb.append(prefix);
} else {
exprs[e++].asString(strb);
}
}
return strb.toString();
}
/**
* Prepares this template by expanding any contained deferred expression.
* @param context the context to prepare against
* @return the prepared version of the template
*/
public Template prepare(JexlContext context) {
JexlEngine.Frame frame = script.createFrame((Object[]) null);
TemplateContext tcontext = new TemplateContext(context, frame, exprs, null);
Expression[] immediates = new Expression[exprs.length];
for (int e = 0; e < exprs.length; ++e) {
immediates[e] = exprs[e].prepare(tcontext);
}
return new Template(prefix, source, script, immediates);
}
/**
* Evaluates this template.
* @param context the context to use during evaluation
* @param writer the writer to use for output
*/
public void evaluate(JexlContext context, Writer writer) {
evaluate(context, writer, (Object[]) null);
}
/**
* Evaluates this template.
* @param context the context to use during evaluation
* @param writer the writer to use for output
* @param args the arguments
*/
public void evaluate(JexlContext context, Writer writer, Object... args) {
JexlEngine.Frame frame = script.createFrame(args);
TemplateContext tcontext = new TemplateContext(context, frame, exprs, writer);
Interpreter interpreter = jexl.createInterpreter(tcontext, !jexl.isLenient(), false);
interpreter.setFrame(frame);
interpreter.interpret(script);
}
}
/**
* The type of context to use during evaluation of templates.
* This context exposes its writer as '$jexl' to the scripts.
* public for introspection purpose.
* @since 2.1
*/
public final class TemplateContext implements JexlContext, NamespaceResolver {
/** The wrapped context. */
private final JexlContext wrap;
/** The array of UnifiedJEXL expressions. */
private final Expression[] exprs;
/** The writer used to output. */
private final Writer writer;
/** The call frame. */
private final JexlEngine.Frame frame;
/**
* Creates a template context instance.
* @param jcontext the base context
* @param jframe the calling frame
* @param expressions the list of expression from the template to evaluate
* @param out the output writer
*/
protected TemplateContext(JexlContext jcontext, JexlEngine.Frame jframe, Expression[] expressions, Writer out) {
wrap = jcontext;
frame = jframe;
exprs = expressions;
writer = out;
}
/**
* Gets this context calling frame.
* @return the engine frame
*/
public JexlEngine.Frame getFrame() {
return frame;
}
/** {@inheritDoc} */
public Object get(String name) {
if ("$jexl".equals(name)) {
return writer;
} else {
return wrap.get(name);
}
}
/** {@inheritDoc} */
public void set(String name, Object value) {
wrap.set(name, value);
}
/** {@inheritDoc} */
public boolean has(String name) {
return wrap.has(name);
}
/** {@inheritDoc} */
public Object resolveNamespace(String ns) {
if ("jexl".equals(ns)) {
return this;
} else if (wrap instanceof NamespaceResolver) {
return ((NamespaceResolver) wrap).resolveNamespace(ns);
} else {
return null;
}
}
/**
* Includes a call to another template.
* Evaluates a template using this template initial context and writer.
* @param template the template to evaluate
* @param args the arguments
*/
public void include(Template template, Object... args) {
template.evaluate(wrap, writer, args);
}
/**
* Prints an expression result.
* @param e the expression number
*/
public void print(int e) {
if (e < 0 || e >= exprs.length) {
return;
}
Expression expr = exprs[e];
if (expr.isDeferred()) {
expr = expr.prepare(wrap);
}
if (expr instanceof CompositeExpression) {
printComposite((CompositeExpression) expr);
} else {
doPrint(expr.evaluate(this));
}
}
/**
* Prints a composite expression.
* @param composite the composite expression
*/
protected void printComposite(CompositeExpression composite) {
Expression[] cexprs = composite.exprs;
final int size = cexprs.length;
Object value = null;
for (int e = 0; e < size; ++e) {
value = cexprs[e].evaluate(this);
doPrint(value);
}
}
/**
* Prints to output.
* This will dynamically try to find the best suitable method in the writer through uberspection.
* Subclassing Writer by adding 'print' methods should be the preferred way to specialize output.
*
* @param arg the argument to print out
*/
private void doPrint(Object arg) {
try {
if (arg instanceof CharSequence) {
writer.write(arg.toString());
} else if (arg != null) {
Object[] value = {arg};
Uberspect uber = getEngine().getUberspect();
JexlMethod method = uber.getMethod(writer, "print", value, null);
if (method != null) {
method.invoke(writer, value);
} else {
writer.write(arg.toString());
}
}
} catch (java.io.IOException xio) {
throw createException("call print", null, xio);
} catch (java.lang.Exception xany) {
throw createException("invoke print", null, xany);
}
}
}
/**
* Whether a sequence starts with a given set of characters (following spaces).
* Space characters at beginning of line before the pattern are discarded.
* @param sequence the sequence
* @param pattern the pattern to match at start of sequence
* @return the first position after end of pattern if it matches, -1 otherwise
* @since 2.1
*/
protected int startsWith(CharSequence sequence, CharSequence pattern) {
int s = 0;
while (Character.isSpaceChar(sequence.charAt(s))) {
s += 1;
}
sequence = sequence.subSequence(s, sequence.length());
if (pattern.length() <= sequence.length()
&& sequence.subSequence(0, pattern.length()).equals(pattern)) {
return s + pattern.length();
} else {
return -1;
}
}
/**
* Reads lines of a template grouping them by typed blocks.
* @param prefix the directive prefix
* @param source the source reader
* @return the list of blocks
* @since 2.1
*/
protected List readTemplate(final String prefix, Reader source) {
try {
int prefixLen = prefix.length();
List blocks = new ArrayList();
BufferedReader reader;
if (source instanceof BufferedReader) {
reader = (BufferedReader) source;
} else {
reader = new BufferedReader(source);
}
StringBuilder strb = new StringBuilder();
BlockType type = null;
while (true) {
CharSequence line = reader.readLine();
if (line == null) {
// at end
TemplateBlock block = new TemplateBlock(type, strb.toString());
blocks.add(block);
break;
} else if (type == null) {
// determine starting type if not known yet
prefixLen = startsWith(line, prefix);
if (prefixLen >= 0) {
type = BlockType.DIRECTIVE;
strb.append(line.subSequence(prefixLen, line.length()));
} else {
type = BlockType.VERBATIM;
strb.append(line.subSequence(0, line.length()));
strb.append('\n');
}
} else if (type == BlockType.DIRECTIVE) {
// switch to verbatim if necessary
prefixLen = startsWith(line, prefix);
if (prefixLen < 0) {
TemplateBlock code = new TemplateBlock(BlockType.DIRECTIVE, strb.toString());
strb.delete(0, Integer.MAX_VALUE);
blocks.add(code);
type = BlockType.VERBATIM;
strb.append(line.subSequence(0, line.length()));
} else {
strb.append(line.subSequence(prefixLen, line.length()));
}
} else if (type == BlockType.VERBATIM) {
// switch to code if necessary(
prefixLen = startsWith(line, prefix);
if (prefixLen >= 0) {
strb.append('\n');
TemplateBlock verbatim = new TemplateBlock(BlockType.VERBATIM, strb.toString());
strb.delete(0, Integer.MAX_VALUE);
blocks.add(verbatim);
type = BlockType.DIRECTIVE;
strb.append(line.subSequence(prefixLen, line.length()));
} else {
strb.append(line.subSequence(0, line.length()));
}
}
}
return blocks;
} catch (IOException xio) {
return null;
}
}
/**
* Creates a new template.
* @param prefix the directive prefix
* @param source the source
* @param parms the parameter names
* @return the template
* @since 2.1
*/
public Template createTemplate(String prefix, Reader source, String... parms) {
return new Template(prefix, source, parms);
}
/**
* Creates a new template.
* @param source the source
* @param parms the parameter names
* @return the template
* @since 2.1
*/
public Template createTemplate(String source, String... parms) {
return new Template("$$", new StringReader(source), parms);
}
/**
* Creates a new template.
* @param source the source
* @return the template
* @since 2.1
*/
public Template createTemplate(String source) {
return new Template("$$", new StringReader(source), (String[]) null);
}
}