org.apache.commons.ognl.enhance
Class ExpressionCompiler

java.lang.Object
  org.apache.commons.ognl.enhance.ExpressionCompiler

All Implemented Interfaces:

OgnlExpressionCompiler

public class ExpressionCompiler
extends Object
implements OgnlExpressionCompiler

Responsible for managing/providing functionality related to compiling generated java source expressions via bytecode enhancements for a given ognl expression.

PRE_CAST

public static final String PRE_CAST

Key used to store any java source string casting statements in the OgnlContext during class compilation.

See Also:

Constant Field Values

loaders

protected Map<ClassResolver,EnhancedClassLoader> loaders

ClassLoader instances.

pool

protected javassist.ClassPool pool

Javassist class definition poool.

classCounter

protected int classCounter

ExpressionCompiler

public ExpressionCompiler()

addCastString

public static void addCastString(OgnlContext context,
                                 String cast)

Used by castExpression(org.apache.commons.ognl.OgnlContext, org.apache.commons.ognl.Node, String) to store the cast java source string in to the current OgnlContext. This will either add to the existing string present if it already exists or create a new instance and store it using the static key of PRE_CAST.

Parameters:

context - The current execution context.

cast - The java source string to store in to the context.

getCastString

public static String getCastString(Class<?> type)

Returns the appropriate casting expression (minus parens) for the specified class type.

For instance, if given an Integer object the string "java.lang.Integer" would be returned. For an array of primitive ints "int[]" and so on..

Parameters:

type - The class to cast a string expression for.

Returns:

The converted raw string version of the class name.

getRootExpression

public static String getRootExpression(Node expression,
                                       Object root,
                                       OgnlContext context)

Convenience method called by many different property/method resolving AST types to get a root expression resolving string for the given node. The callers are mostly ignorant and rely on this method to properly determine if the expression should be cast at all and take the appropriate actions if it should.

Parameters:

expression - The node to check and generate a root expression to if necessary.

root - The root object for this execution.

context - The current execution context.

Returns:

Either an empty string or a root path java source string compatible with javassist compilations from the root object up to the specified Node.

shouldCast

public static boolean shouldCast(Node expression)

Used by getRootExpression(org.apache.commons.ognl.Node, Object, org.apache.commons.ognl.OgnlContext) to determine if the expression needs to be cast at all.

Parameters:

expression - The node to check against.

Returns:

Yes if the node type should be cast - false otherwise.

castExpression

public String castExpression(OgnlContext context,
                             Node expression,
                             String body)

Used primarily by AST types like ASTChain where foo.bar.id type references may need to be cast multiple times in order to properly resolve the members in a compiled statement.

This method should be using the various OgnlContext.getCurrentType() / OgnlContext.getCurrentAccessor() methods to inspect the type stack and properly cast to the right classes - but only when necessary.

Specified by:

castExpression in interface OgnlExpressionCompiler

Parameters:

context - The current execution context.

expression - The node being checked for casting.

body - The java source string generated by the given node.

Returns:

The body string parameter plus any additional casting syntax needed to make the expression resolvable.

getClassName

public String getClassName(Class<?> clazz)

Gets a javassist safe class string for the given class instance. This is especially useful for handling array vs. normal class casting strings.

Specified by:

getClassName in interface OgnlExpressionCompiler

Parameters:

clazz - The class to get a string equivalent javassist compatible string reference for.

Returns:

The string equivalent of the class.

getSuperOrInterfaceClass

public Class<?> getSuperOrInterfaceClass(Method m,
                                         Class<?> clazz)

For the given Method and class finds the highest level interface class this combination can be cast to.

Specified by:

getSuperOrInterfaceClass in interface OgnlExpressionCompiler

Parameters:

m - The method the class must implement.

clazz - The current class being worked with.

Returns:

The highest level interface / class that the referenced Method is declared in.

containsMethod

public boolean containsMethod(Method m,
                              Class<?> clazz)

Helper utility method used by compiler to help resolve class->method mappings during method calls to OgnlExpressionCompiler.getSuperOrInterfaceClass(java.lang.reflect.Method, Class).

Parameters:

m - The method to check for existance of.

clazz - The class to check for the existance of a matching method definition to the method passed in.

Returns:

True if the class contains the specified method, false otherwise.

getInterfaceClass

public Class<?> getInterfaceClass(Class<?> clazz)

Used in places where the preferred OgnlExpressionCompiler.getSuperOrInterfaceClass(java.lang.reflect.Method, Class) isn't possible because the method isn't known for a class. Attempts to upcast the given class to the next available non-private accessible class so that compiled expressions can reference the interface class of an instance so as not to be compiled in to overly specific statements.

Specified by:

getInterfaceClass in interface OgnlExpressionCompiler

Parameters:

clazz - The class to attempt to find a compatible interface for.

Returns:

The same class if no higher level interface could be matched against or the interface equivalent class.

getRootExpressionClass

public Class<?> getRootExpressionClass(Node rootNode,
                                       OgnlContext context)

For a given root object type returns the base class type to be used in root referenced expressions. This helps in some instances where the root objects themselves are compiled javassist instances that need more generic class equivalents to cast to.

Specified by:

getRootExpressionClass in interface OgnlExpressionCompiler

Parameters:

rootNode - The root expression node.

context - The current execution context.

Returns:

The root expression class type to cast to for this node.

compileExpression

public void compileExpression(OgnlContext context,
                              Node expression,
                              Object root)
                       throws Exception

The core method executed to compile a specific expression. It is expected that this expression always return a Node with a non null Node.getAccessor() instance - unless an exception is thrown by the method or the statement wasn't compilable in this instance because of missing/null objects in the expression. These instances may in some cases continue to call this compilation method until the expression is resolvable.

Specified by:

compileExpression in interface OgnlExpressionCompiler

Parameters:

context - The context of execution.

expression - The pre-parsed root expression node to compile.

root - The root object for the expression - may be null in many instances so some implementations may exit

Throws:

Exception - If an error occurs compiling the expression and no strategy has been implemented to handle incremental expression compilation for incomplete expression members.

generateGetter

protected String generateGetter(OgnlContext context,
                                javassist.CtClass newClass,
                                javassist.CtClass objClass,
                                javassist.ClassPool classPool,
                                javassist.CtMethod valueGetter,
                                Node expression,
                                Object root)
                         throws Exception

Throws:

Exception

createLocalReference

public String createLocalReference(OgnlContext context,
                                   String expression,
                                   Class<?> type)

Method is used for expressions where multiple inner parameter method calls in generated java source strings cause javassit failures. It is hacky and cumbersome to have to generate expressions this way but it's the only current known way to make javassist happy.

Takes an expression block generated by a node and creates a new method on the base object being compiled so that sufficiently complicated sub expression blocks can be broken out in to distinct methods to be referenced by the core accessor / setter methods in the base compiled root object.

Specified by:

createLocalReference in interface OgnlExpressionCompiler

Parameters:

context - The current execution context.

expression - The java source expression to dump in to a seperate method reference.

type - The return type that should be specified for the new method.

Returns:

The method name that will be used to reference the sub expression in place of the actual sub expression itself.

generateSetter

protected String generateSetter(OgnlContext context,
                                javassist.CtClass newClass,
                                javassist.CtClass objClass,
                                javassist.ClassPool classPool,
                                javassist.CtMethod valueSetter,
                                Node expression,
                                Object root)
                         throws Exception

Throws:

Exception

generateOgnlGetter

protected String generateOgnlGetter(javassist.CtClass clazz,
                                    javassist.CtMethod valueGetter,
                                    javassist.CtField node)
                             throws Exception

Fail safe getter creation when normal compilation fails.

Parameters:

clazz - The javassist class the new method should be attached to.

valueGetter - The method definition the generated code will be contained within.

node - The root expression node.

Returns:

The generated source string for this method, the method will still be added via the javassist API either way so this is really a convenience for exception reporting / debugging.

Throws:

Exception - If a javassist error occurs.

generateOgnlSetter

protected String generateOgnlSetter(javassist.CtClass clazz,
                                    javassist.CtMethod valueSetter,
                                    javassist.CtField node)
                             throws Exception

Fail safe setter creation when normal compilation fails.

Parameters:

clazz - The javassist class the new method should be attached to.

valueSetter - The method definition the generated code will be contained within.

node - The root expression node.

Returns:

The generated source string for this method, the method will still be added via the javassist API either way so this is really a convenience for exception reporting / debugging.

Throws:

Exception - If a javassist error occurs.

getClassLoader

protected EnhancedClassLoader getClassLoader(OgnlContext context)

Creates a ClassLoader instance compatible with the javassist classloader and normal OGNL class resolving semantics.

Parameters:

context - The current execution context.

Returns:

The created ClassLoader instance.

getCtClass

protected javassist.CtClass getCtClass(Class<?> searchClass)
                                throws javassist.NotFoundException

Loads a new class definition via javassist for the specified class.

Parameters:

searchClass - The class to load.

Returns:

The javassist class equivalent.

Throws:

javassist.NotFoundException - When the class definition can't be found.

getClassPool

protected javassist.ClassPool getClassPool(OgnlContext context,
                                           EnhancedClassLoader loader)

Gets either a new or existing ClassPool for use in compiling javassist classes. A new class path object is inserted in to the returned ClassPool using the passed in loader instance if a new pool needs to be created.

Parameters:

context - The current execution context.

loader - The ClassLoader instance to use - as returned by getClassLoader(org.apache.commons.ognl.OgnlContext).

Returns:

The existing or new ClassPool instance.