org.apache.derby.impl.services.bytecode
Class BCJava

java.lang.Object
  extended byorg.apache.derby.impl.services.bytecode.BCJava
All Implemented Interfaces:
CacheableFactory, JavaFactory, ModuleControl

public class BCJava
extends java.lang.Object
implements JavaFactory, CacheableFactory, ModuleControl

Debugging problems with generated classes

When the code has been generated incorrectly, all sorts of odd things can go wrong. This is one recommended approach to finding the problem.

First, turn on ByteCodeGenInstr and DumpClassFile. Look for missing files (right now they are consecutively numbered by the activation class builder; later on they won't be, but BytCodeGenInstr dumps messages about the classes it has). Look at the log to make sure that all "GEN starting class/method" messages are paired with a "GEN ending class/method" message. If a file is missing or the pairing is missing, then something went wrong when the system tried to generate the bytecodes. Resort to your favorite debugging tool to step through the faulty statement.

If you get class files but the system crashes on you (I had an OS segmentation fault once) or you get funny messages like JDBC Excpetion: ac5 where ac5 is just the name of a generated class, then one of the following is likely:

The best way to locate the problem here is to do this (replace ac5.class with the name of your class file):
  1. javap -c -v ac5 >ac5.gp
    if javap reports "Class not found", and the file ac5.class does exist in the current directory, then the .class file is probably corrupt. Try running mocha on it to see if that works. The problem will be in the code that generates the entries for the class file -- most likely the ConstantPool is bad, an attribute got created incorrectly, or perhaps the instruction streams are goofed up.
  2. java mocha.Decompiler ac5.class
    if mocha cannot create good java source, then you really need to go back and examine the calls creating the java constructs; a parameter might have been null when it should have, a call to turn an expression into a statement may be missing, or something else may be wrong.
  3. mv ac5.mocha ac5.java
  4. vi ac5.java ; you will have to fix any new SQLBoolean(1, ...) calls to be new SQLBoolean(true, ...). Also mocha occasionally messes up other stuff too. Just iterate on it until it builds or you figure out what is wrong with the generated code.
  5. javac ac5.java
  6. javap -v -c ac5 >ac5.jp
  7. sed '1,$s/#[0-9]* ac5.gn
  8. sed '1,$s/#[0-9]* ac5.jn
    These seds are to get rid of constant pool entry numbers, which will be wildly different on the two files.
  9. vdiff32 ac5.gn ac5.jn
    this tool shows you side-by-side diffs. If you change to the window that interleaves the diffs, you can see the length of the line. Look for places where there are invokevirtual vs. invokeinterface differences, differences in the class name of a field, differences in the class name of a method parameter or return type. The generated code will* have some unavoidable differences from the compiled code, such as: Once you find a diff, you need to track down where the call was generated and modify it appropriately: change newMethodCall to newInterfaceMethodCall; add newCastExpression to get a argument into the right type for the parameter; ensure the return type given for the method is its declared return type.

Author:
ames
See Also:
JavaFactory

Field Summary
private  CacheManager vmTypeIdCache
           
 
Fields inherited from interface org.apache.derby.iapi.services.compiler.JavaFactory
JAVA_FACTORY_PROPERTY
 
Constructor Summary
BCJava()
           
 
Method Summary
 void boot(boolean create, java.util.Properties properties)
          Start this module.
 Cacheable newCacheable(CacheManager cm)
           
 ClassBuilder newClassBuilder(ClassFactory cf, java.lang.String packageName, int modifiers, java.lang.String className, java.lang.String superClass)
          a class.
 void stop()
          Stop this module.
(package private)  Type type(java.lang.String javaType)
          Get the VM Type ID that corresponds with the given java type name.
(package private)  java.lang.String vmType(BCMethodDescriptor md)
           
(package private) static short vmTypeId(java.lang.String vmTypeS)
          Map vm types as strings to vm types as the VM handles, with int ids.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

vmTypeIdCache

private CacheManager vmTypeIdCache
Constructor Detail

BCJava

public BCJava()
Method Detail

boot

public void boot(boolean create,
                 java.util.Properties properties)
          throws StandardException
Start this module. We need a read/write version of the class utilities

Specified by:
boot in interface ModuleControl
Throws:
StandardException - standard cloudscape policy
See Also:
Monitor, ModuleFactory

stop

public void stop()
Stop this module. In this case, nothing needs to be done.

Specified by:
stop in interface ModuleControl
See Also:
Monitor, ModuleFactory

newClassBuilder

public ClassBuilder newClassBuilder(ClassFactory cf,
                                    java.lang.String packageName,
                                    int modifiers,
                                    java.lang.String className,
                                    java.lang.String superClass)
a class. Once it is created, fields, methods, interfaces, static initialization code, and constructors can be added to it. Java: package #packageName; #modifiers #className extends #superClass { } // modifiers is the | of the JVM constants for // the modifiers such as static, public, etc.

Specified by:
newClassBuilder in interface JavaFactory
Parameters:
packageName - the name of the package the class is in. null if it is in the default package.
modifiers - the | of the Modifiers constants representing the visibility and control of this method.
className - the name of the class or interface
superClass - the name of the superclass or superinterface
cf - ClassFactory to be used for class resolution (debug only) and loading of the generated class.
Returns:
the class builder.
See Also:
java.lang.reflect.Modifiers

newCacheable

public Cacheable newCacheable(CacheManager cm)
Specified by:
newCacheable in interface CacheableFactory

type

Type type(java.lang.String javaType)
Get the VM Type ID that corresponds with the given java type name. This uses the cache of VM type ids.

Parameters:
javaType - The java type name to translate to a java VM type id
Returns:
The java VM type ID

vmType

java.lang.String vmType(BCMethodDescriptor md)

vmTypeId

static short vmTypeId(java.lang.String vmTypeS)
Map vm types as strings to vm types as the VM handles, with int ids. Used in mapping opcodes based on type of operand/stack entry available.



Apache Derby V10.0 Engine Documentation - Copyright © 1997,2004 The Apache Software Foundation or its licensors, as applicable.