Generating interface with ASM is not working - java

I need to generate an interface at runtime. This interface will be used in a dynamic proxy. At first, I found this article from Google, but then I found I could just use ASM instead. Here is my code that gets the bytecode of the interface:
private static byte[] getBytecode(String internalName, String genericClassTypeSignature, Method[] methods, Class<?>... extendedInterfaces) throws IOException {
ClassWriter cw = new ClassWriter(0);
String[] interfaces = new String[extendedInterfaces.length];
int i = 0;
for (Class<?> interfac : extendedInterfaces) {
interfaces[i] = interfac.getName().replace('.', '/');
i++;
}
cw.visit(V1_6, ACC_PUBLIC + ACC_ABSTRACT + ACC_INTERFACE, internalName, null, "java/lang/Object", interfaces);
ArrayList<String> exceptions = new ArrayList<String>();
for (Method m : methods) {
exceptions.clear();
for (Class<?> exception : m.getExceptionTypes()) {
exceptions.add(getInternalNameOf(exception));
}
cw.visitMethod(removeInvalidAbstractModifiers(m.getModifiers()) + ACC_ABSTRACT, m.getName(), getMethodDescriptorOf(m), getTypeSignatureOf(m), exceptions.toArray(new String[exceptions.size()]));
}
cw.visitEnd();
return cw.toByteArray();
}
private static int removeInvalidAbstractModifiers(int mod) {
int result = 0;
if (Modifier.isProtected(mod)) {
result += ACC_PROTECTED;
}
if (Modifier.isPublic(mod)) {
result += ACC_PUBLIC;
}
if (Modifier.isTransient(mod)) {
result += ACC_VARARGS;
}
return result;
}
Just for test purposes, I tried to convert JFrame to an interface. But when I load my generated interface, it gives me a java.lang.ClassFormatError:
java.lang.ClassFormatError: Method paramString in class javax/swing/JFrame$GeneratedInterface has illegal modifiers: 0x404
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
// ...
Modifier.toString(0x404) tells me that 0x404 means protected abstract. As far as I know, a protected abstract method in an abstract class is perfectly legal.
Here is the code for the paramString method (see above) in JFrame:
/**
* Returns a string representation of this <code>JFrame</code>.
* This method
* is intended to be used only for debugging purposes, and the
* content and format of the returned string may vary between
* implementations. The returned string may be empty but may not
* be <code>null</code>.
*
* #return a string representation of this <code>JFrame</code>
*/
protected String paramString() {
String defaultCloseOperationString;
if (defaultCloseOperation == HIDE_ON_CLOSE) {
defaultCloseOperationString = "HIDE_ON_CLOSE";
} else if (defaultCloseOperation == DISPOSE_ON_CLOSE) {
defaultCloseOperationString = "DISPOSE_ON_CLOSE";
} else if (defaultCloseOperation == DO_NOTHING_ON_CLOSE) {
defaultCloseOperationString = "DO_NOTHING_ON_CLOSE";
} else if (defaultCloseOperation == 3) {
defaultCloseOperationString = "EXIT_ON_CLOSE";
} else defaultCloseOperationString = "";
String rootPaneString = (rootPane != null ?
rootPane.toString() : "");
String rootPaneCheckingEnabledString = (rootPaneCheckingEnabled ?
"true" : "false");
return super.paramString() +
",defaultCloseOperation=" + defaultCloseOperationString +
",rootPane=" + rootPaneString +
",rootPaneCheckingEnabled=" + rootPaneCheckingEnabledString;
}
I see no reason why I should be getting this error. Could someone explain this to me?

Methods in an interface must be public.
Also, in your removeInvalidAbstractModifiers() method, you should be using |= to set a flag, rather than +=. The latter will cause problems if the flag is already set (which I realize it won't be if starting from 0, but it's a good habit to get into). Although why you're setting the flag in a method called "remove," I have no idea.

Related

Initialize multiple numeric fields at once in JAVA that begin with certain values

I am working on a Java class that contains a ton of numeric fields. Most of them would begin with something like 'CMTH' or 'FYTD'. Is it possible to initialize all fields of the same type that begin or end with a certain value. For example I have the following fields:
CMthRepCaseACR CMthRepUnitACR CMthRecCaseACR CMthRecUnitACR CMthHecCaseACR CMthHecUnitACR FYTDHecCaseACR FYTDHecUnitACR CMthBBKCaseACR CMthBBKUnitACR CMthPIHCaseACR .
I am trying to figure if it is possible to initialize all fields to zero that end with an 'ACR' or begin with an 'Cmth"
I know I can do something like cmtha = cmthb = cmthc = 0 but I was wondering there was a command where you can some kind of mask to initialize
Thanks
Assuming that you cannot change that said Java class (and e.g. use a collection or map to store the values) your best bet is probably reflection (see also: Trail: The Reflection API). Reflection gives you access to all fields of the class and you can then implement whatever matching you'd like.
Here's a short demo to get you started, minus error handling, sanity checks and adaptions to your actual class:
import java.util.stream.Stream;
public class Demo {
private static class DemoClass {
private int repCaseACR = 1;
private int CMthRepUnit = 2;
private int foo = 3;
private int bar = 4;
#Override
public String toString() {
return "DemoClass [repCaseACR=" + repCaseACR + ", CMthRepUnit=" + CMthRepUnit + ", foo=" + foo + ", bar="
+ bar + "]";
}
}
public static void main(String[] args) {
DemoClass demoClass = new DemoClass();
System.out.println("before: " + demoClass);
resetFields(demoClass, "CMth", null);
System.out.println("after prefix reset: " + demoClass);
resetFields(demoClass, null, "ACR");
System.out.println("after suffix reset: " + demoClass);
}
private static void resetFields(DemoClass instance, String prefix, String suffix) {
Stream.of(instance.getClass().getDeclaredFields())
.filter(field ->
(prefix != null && field.getName().startsWith(prefix))
|| (suffix != null && field.getName().endsWith(suffix)))
.forEach(field -> {
field.setAccessible(true);
try {
field.set(instance, 0);
} catch (IllegalArgumentException | IllegalAccessException e) {
// TODO handle me
}
});
}
}
Output:
before: DemoClass [repCaseACR=1, CMthRepUnit=2, foo=3, bar=4]
after prefix reset: DemoClass [repCaseACR=1, CMthRepUnit=0, foo=3, bar=4]
after suffix reset: DemoClass [repCaseACR=0, CMthRepUnit=0, foo=3, bar=4]
Note: Both links are seriously dated but the core functionality of reflection is still the same.

Refactor parameter names programmatically

Using eclipse's jdt refactoring framework, I am trying to convert two different code bases to the same names. They are almost identical codebases except that names are different.
Function/Field/Class renaming works fine, but when it comes to parameters it yells at me that the workbench is not created yet. However i'm trying to do this in a headless manor.
private void refactor(String task, IJavaElement element, String new_name) throws CoreException
{
RefactoringStatus status = new RefactoringStatus();
RefactoringContribution contrib = RefactoringCore.getRefactoringContribution(task);
RenameJavaElementDescriptor rnDesc = (RenameJavaElementDescriptor)contrib.createDescriptor();
rnDesc.setFlags(JavaRefactoringDescriptor.JAR_MIGRATION | JavaRefactoringDescriptor.JAR_REFACTORING);
rnDesc.setProject(element.getJavaProject().getProject().getName());
rnDesc.setUpdateReferences(true);
rnDesc.setJavaElement(element);
rnDesc.setNewName(new_name);
Refactoring ref = rnDesc.createRefactoring(status);
ref.checkInitialConditions(NULL_MON);
ref.checkFinalConditions(NULL_MON);
Change change = ref.createChange(NULL_MON);
change.perform(NULL_MON);
}
This works fine:
for (IMethod method : type.getMethods())
{
refactor(IJavaRefactorings.RENAME_METHOD, method, {new name});
}
This does not:
for (IMethod method : type.getMethods())
{
for (ILocalVariable param : method.getParameters())
{
refactor(IJavaRefactorings.RENAME_LOCAL_VARIABLE, param, {new name});
}
}
And the error, not really helpful as I said I need to do this in a headless manor {so can't make workbench}
java.lang.IllegalStateException: Workbench has not been created yet.
at org.eclipse.ui.PlatformUI.getWorkbench(PlatformUI.java:92)
at org.eclipse.jdt.internal.ui.javaeditor.ASTProvider.install(ASTProvider.java:245)
at org.eclipse.jdt.internal.ui.javaeditor.ASTProvider.<init>(ASTProvider.java:236)
at org.eclipse.jdt.internal.ui.JavaPlugin.getASTProvider(JavaPlugin.java:710)
at org.eclipse.jdt.ui.SharedASTProvider.getAST(SharedASTProvider.java:128)
at org.eclipse.jdt.internal.corext.refactoring.util.RefactoringASTParser.parseWithASTProvider(RefactoringASTParser.java:119)
at org.eclipse.jdt.internal.corext.refactoring.rename.RenameLocalVariableProcessor.initAST(RenameLocalVariableProcessor.java:231)
at org.eclipse.jdt.internal.corext.refactoring.rename.RenameLocalVariableProcessor.checkInitialConditions(RenameLocalVariableProcessor.java:218)
at org.eclipse.ltk.core.refactoring.participants.ProcessorBasedRefactoring.checkInitialConditions(ProcessorBasedRefactoring.java:203)
UPDATE: Made some progress, now I can refactor functions that are not overrides. But any function that overrides another or an interface screws up:
F_ARGUMENTS = JavaRefactoringDescriptor.class.getDeclaredField("fArguments");
F_ARGUMENTS.setAccessible(true);
private void refactor(IMethod method, String[] names) throws CoreException
{
/* My attempt to fix the interface issues, causes duplicate functions instead of renaming the parameters
IMethod parent = null;
if (method.getDeclaringType().isInterface())
{
parent = MethodChecks.overridesAnotherMethod(method, method.getDeclaringType().newSupertypeHierarchy(NULL_MON));
}
else if (MethodChecks.isVirtual(method))
{
ITypeHierarchy hierarchy = method.getDeclaringType().newTypeHierarchy(NULL_MON);
parent = MethodChecks.isDeclaredInInterface(method, hierarchy, NULL_MON);
if (parent == null)
{
parent = MethodChecks.overridesAnotherMethod(method, hierarchy);
}
}
parent = (parent == null ? method : parent);
if (!method.equals(parent))
{
refactor(parent, names);
return;
}*/
String task = IJavaRefactorings.CHANGE_METHOD_SIGNATURE;
RefactoringStatus status = new RefactoringStatus();
ChangeMethodSignatureRefactoringContribution contrib = (ChangeMethodSignatureRefactoringContribution)RefactoringCore.getRefactoringContribution(task);
ChangeMethodSignatureDescriptor desc = (ChangeMethodSignatureDescriptor)contrib.createDescriptor();
desc.setFlags(JavaRefactoringDescriptor.JAR_MIGRATION |
JavaRefactoringDescriptor.JAR_REFACTORING |
RefactoringDescriptor.MULTI_CHANGE |
RefactoringDescriptor.STRUCTURAL_CHANGE);
Map<String, String> args = null;
try
{
args = (Map<String, String>)F_ARGUMENTS.get(desc);
}
catch (Exception e)
{
e.printStackTrace();
}
String project = method.getJavaProject().getProject().getName();
desc.setProject(method.getJavaProject().getProject().getName());
args.put("input", JavaRefactoringDescriptorUtil.elementToHandle(project, method));
args.put("name", method.getElementName());
args.put("deprecate", "false");
args.put("delegate", "true");
boolean changed = false;
int x = 0;
for (ILocalVariable param : method.getParameters())
{
if (!param.getElementName().equals(names[x]))
{
changed = true;
}
String type = "String"; //Doesn't seem to actually matter as long as they are both the same
String info = type + " " + param.getElementName() + " " + x + " " +
type + " " + names[x] + " false";
args.put("parameter" + (x + 1), info);
x++;
}
if (changed)
{
refactor(desc.createRefactoring(status));
}
}
This is what I came up with:
ChangeSignatureProcessor changeSignatureProcessor = new ChangeSignatureProcessor((IMethod) node.resolveBinding().getJavaElement());
ParameterInfo info=new ParameterInfo("FormContext", "formContext", ParameterInfo.INDEX_FOR_ADDED);
info.setDefaultValue("formContext");
changeSignatureProcessor.getParameterInfos().add(0,info);
RefactoringStatus status = new RefactoringStatus();
CheckConditionsContext context= new CheckConditionsContext();
context.add(new ValidateEditChecker(null));
context.add(new ResourceChangeChecker());
changeSignatureProcessor.checkInitialConditions(monitor);
changeSignatureProcessor.checkFinalConditions(monitor,context);
changeSignatureProcessor.createChange(monitor).perform(monitor);

How to combine 2 java methods into one efficiently

I'm trying to create a validate java class that receives 4 inputs from an object passed as 1 from the requester. The class needs to convert float inputs to string and evaluate each input to meet a certain format and then throw exceptions complete with error message and code when it fails.
What I have is in two methods and would like to know if there is a better way to combine these two classes into one validate method for the main class to call. I don't seem to be able to get around using the pattern/matcher concept to insure the inputs are formatted correctly. Any help you can give would be very much appreciated.
public class Validator {
private static final String MoneyPattern ="^\\d{1,7}(\\.\\d{1,2})$" ;
private static final String PercentagePattern = "^\\d{1,3}\\.\\d{1,2}$";
private static final String CalendarYearPattern = "^20[1-9][0-9]$";
private int errorcode = 0;
private String errormessage = null;
public Validator(MyInput input){
}
private boolean verifyInput(){
String Percentage = ((Float) input.getPercentage().toString();
String Income = ((Float) input.getIncome().toString();
String PublicPlan = ((Float) input.getPublicPlan().toString();
String Year = ((Float) input.getYear();
try {
if (!doesMatch(Income, MoneyPattern)) {
errormessage = errormessage + "income,";
}
if (!doesMatch(PublicPlan, MoneyPattern)) {
errormessage = errormessage + "insurance plan,";
}
if (!doesMatch(Percentage, PercentagePattern)) {
errormessage = errormessage + "Percentage Plan,";
}
if (!doesMatch(Year, CalendarYearPattern)) {
errormessage = errormessage + "Year,";
}
} catch (Exception e){
errorcode = 111;
errormessage = e.getMessage();
}
}
private boolean doesMatch(String s, String pattern) throws Exception{
try {
Pattern p = Pattern.compile(pattern);
Matcher m = p.matcher(s);
if (!s.equals("")){
if(m.find()){
return true;
} else {
return false;
}
}else {
return false;
}
} catch (PatternSyntaxException pse){
errorcode = 111;
errormessage = pse.getMessage();
}
}
}
This code is borked from the word "go". You have a constructor into which you pass a MyInput reference, but there's no code in the ctor and no private data member to receive it. It looks like you expect to use input in your doesMatch() method, but it's a NullPointerException waiting to happen.
Your code doesn't follow the Sun Java coding standards; variable names should be lower case.
Why you wouldn't do that input validation in the ctor, when you actually receive the value, is beyond me. Perhaps you really meant to pass it into that verifyInput() method.
I would worry about correctness and readability before concerning myself with efficiency.
I'd have methods like this:
public boolean isValidMoney(String money) { // put the regex here }
public boolean isValidYear(String year) { // the regex here }
I think I'd prefer a real Money class to a String. There's no abstraction whatsoever.
Here's one bit of honesty:
private static final String CalendarYearPattern = "^20[1-9][0-9]$";
I guess you either don't think this code will still be running in the 22nd century or you won't be here to maintain it.
One way of doing this would be with DynamicBeans.
package com.acme.validator;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.apache.commons.beanutils.PropertyUtils;
public class Validator {
//A simple optimisation of the pattern
private static final Pattern MoneyPattern = Pattern.compile("^\\d{1,7}(\\.\\d{1,2})$");
private static final Pattern PercentagePattern = Pattern.compile("^\\d{1,3}\\.\\d{1,2}$");
private static final Pattern CalendarYearPattern = Pattern.compile("^20[1-9][0-9]$");
public String Validator(MyInput input) {
String errormessage = "";
/*
* Setting these up as Maps.
* Ideally this would be a 'simple bean'
* but that goes beyond the scope of the
* original question
*/
Map<String,Pattern> patternMap = new HashMap<String,Pattern>();
patternMap.put("percentage", PercentagePattern);
patternMap.put("publicPlan", MoneyPattern);
patternMap.put("income", MoneyPattern);
patternMap.put("year", CalendarYearPattern);
Map<String,String> errorMap = new HashMap<String,String>();
errorMap.put("percentage", "Percentage Plan,");
errorMap.put("publicPlan", "insurance plan,");
errorMap.put("income", "income,");
errorMap.put("year", "Year,");
for (String key : patternMap.keySet()) {
try {
String match = ((Float) PropertyUtils.getSimpleProperty(input, key)).toString();
Matcher m = patternMap.get(key).matcher(match);
if ("".equals(match) || !m.find()) {
errormessage = errormessage + errorMap.get(key);
}
} catch (Exception e) {
errormessage = e.getMessage(); //since getMessage() could be null, you need to work out some way of handling this in the response
//don't know the point of the error code so remove this altogether
break; //Assume an exception trumps any validation failure
}
}
return errormessage;
}
}
I've made a few assumptions about the validation rules (for simplicity used 2 maps but you could also use a single map and a bean containing both the Pattern and the Message and even the 'error code' if that is important).
The key 'flaw' in your original setup and what would hamper the solution above, is that you are using 'year' as Float in the input bean.
(new Float(2012)).toString()
The above returns "2012.0". This will always fail your pattern. When you start messing about with the different types of objects potentially in the input bean, you may need to consider ensuring they are String at the time of creating the input bean and not, as is the case here, when they are retrieved.
Good Luck with the rest of your Java experience.

Remove attributes from XMLBean

Assume there's an XMLBeans XmlObject with attributes, how can I get selected attributes in single step?
I'm expecting like something ....
removeAttributes(XmlObject obj, String[] selectableAttributes){};
Now the above method should return me the XMLObject with only those attributes.
Assumption: the attributes that you want to remove from your XmlObject must be optional in the corresponding XML Schema. Under this assumption, XMLBeans provides you with a couple of useful methods: unsetX and isSetX (where X is your attribute name. So, we can implement a removeAttributes method in this way:
public void removeAttributes(XmlObject obj,
String[] removeAttributeNames)
throws IllegalArgumentException, IllegalAccessException,
InvocationTargetException, SecurityException,
NoSuchMethodException {
Class<?> clazz = obj.getClass();
for (int i = 0; i < removeAttributeNames.length; i++) {
String attrName =
removeAttributeNames[i].substring(0, 1).toUpperCase() +
removeAttributeNames[i].substring(1);
String isSetMethodName = "isSet" + attrName;
Boolean isSet = null;
try {
Method isSetMethod = clazz.getMethod(isSetMethodName);
isSet = (Boolean) isSetMethod.invoke(obj, new Object[] {});
} catch (NoSuchMethodException e) {
System.out.println("attribute " + removeAttributeNames[i]
+ " is not optional");
}
if (isSet != null && isSet.booleanValue() == true) {
String unsetMethodName = "unset" + attrName;
Method unsetMethod = clazz.getMethod(unsetMethodName);
unsetMethod.invoke(obj, new Object[] {});
}
}
}
Note 1: I have slightly modified the semantics of your method signature: the second argument (the String[]) is actually the list of attributes that you want to remove. I think this is more consistent with the method name (removeAttributes), and it also simplify things (using unsetX and isSetX).
Note 2: The reason for calling isSetX before calling unsetX is that unsetX would throw an InvocationTargetException if called when the attribute X is not set.
Note 3: You may want to change exception handling according to your needs.
I think you can use a cursor ... they are cumbersome to handle, but so is reflection.
public static XmlObject RemoveAllAttributes(XmlObject xo) {
return RemoveAllofType(xo, TokenType.ATTR);
}
public static XmlObject RemoveAllofTypes(XmlObject xo, final TokenType... tts) {
printTokens(xo);
final XmlCursor xc = xo.newCursor();
while (TokenType.STARTDOC == xc.currentTokenType() || TokenType.START == xc.currentTokenType()) {
xc.toNextToken();
}
while (TokenType.ENDDOC != xc.currentTokenType() && TokenType.STARTDOC != xc.prevTokenType()) {
if (ArrayUtils.contains(tts, xc.currentTokenType())) {
xc.removeXml();
continue;
}
xc.toNextToken();
}
xc.dispose();
return xo;
}
I am using this simple method to clean everything in the element. You can omit the cursor.removeXmlContents to only delete attributes. Second cursor is used to return to the initial position:
public static void clearElement(final XmlObject object)
{
final XmlCursor cursor = object.newCursor();
cursor.removeXmlContents();
final XmlCursor start = object.newCursor();
while (cursor.toFirstAttribute())
{
cursor.removeXml();
cursor.toCursor(start);
}
start.dispose();
cursor.dispose();
}

Creating classes dynamically with Java

I have tried to find information about this but have come up empty handed:
I gather it is possible to create a class dynamically in Java using reflection or proxies but I can't find out how. I'm implementing a simple database framework where I create the SQL queries using reflection. The method gets the object with the database fields as a parameter and creates the query based on that. But it would be very useful if I could also create the object itself dynamically so I wouldn't have the need to have a simple data wrapper object for each table.
The dynamic classes would only need simple fields (String, Integer, Double), e.g.
public class Data {
public Integer id;
public String name;
}
Is this possible and how would I do this?
EDIT: This is how I would use this:
/** Creates an SQL query for updating a row's values in the database.
*
* #param entity Table name.
* #param toUpdate Fields and values to update. All of the fields will be
* updated, so each field must have a meaningful value!
* #param idFields Fields used to identify the row(s).
* #param ids Id values for id fields. Values must be in the same order as
* the fields.
* #return
*/
#Override
public String updateItem(String entity, Object toUpdate, String[] idFields,
String[] ids) {
StringBuilder sb = new StringBuilder();
sb.append("UPDATE ");
sb.append(entity);
sb.append("SET ");
for (Field f: toUpdate.getClass().getDeclaredFields()) {
String fieldName = f.getName();
String value = new String();
sb.append(fieldName);
sb.append("=");
sb.append(formatValue(f));
sb.append(",");
}
/* Remove last comma */
sb.deleteCharAt(sb.toString().length()-1);
/* Add where clause */
sb.append(createWhereClause(idFields, ids));
return sb.toString();
}
/** Formats a value for an sql query.
*
* This function assumes that the field type is equivalent to the field
* in the database. In practice this means that this field support two
* types of fields: string (varchar) and numeric.
*
* A string type field will be escaped with single parenthesis (') because
* SQL databases expect that. Numbers are returned as-is.
*
* If the field is null, a string containing "NULL" is returned instead.
*
* #param f The field where the value is.
* #return Formatted value.
*/
String formatValue(Field f) {
String retval = null;
String type = f.getClass().getName();
if (type.equals("String")) {
try {
String value = (String)f.get(f);
if (value != null) {
retval = "'" + value + "'";
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
} else if (type.equals("Integer")) {
try {
Integer value = (Integer)f.get(f);
if (value != null) {
retval = String.valueOf(value);
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
} else {
try {
String value = (String) f.get(f);
if (value != null) {
retval = value;
} else {
retval = "NULL";
}
} catch (Exception e) {
System.err.println("No such field: " + e.getMessage());
}
}
return retval;
}
There are many different ways to achieve this (e.g proxies, ASM), but the simplest approach, one that you can start with when prototyping is:
import java.io.*;
import java.util.*;
import java.lang.reflect.*;
public class MakeTodayClass {
Date today = new Date();
String todayMillis = Long.toString(today.getTime());
String todayClass = "z_" + todayMillis;
String todaySource = todayClass + ".java";
public static void main (String args[]){
MakeTodayClass mtc = new MakeTodayClass();
mtc.createIt();
if (mtc.compileIt()) {
System.out.println("Running " + mtc.todayClass + ":\n\n");
mtc.runIt();
}
else
System.out.println(mtc.todaySource + " is bad.");
}
public void createIt() {
try {
FileWriter aWriter = new FileWriter(todaySource, true);
aWriter.write("public class "+ todayClass + "{");
aWriter.write(" public void doit() {");
aWriter.write(" System.out.println(\""+todayMillis+"\");");
aWriter.write(" }}\n");
aWriter.flush();
aWriter.close();
}
catch(Exception e){
e.printStackTrace();
}
}
public boolean compileIt() {
String [] source = { new String(todaySource)};
ByteArrayOutputStream baos= new ByteArrayOutputStream();
new sun.tools.javac.Main(baos,source[0]).compile(source);
// if using JDK >= 1.3 then use
// public static int com.sun.tools.javac.Main.compile(source);
return (baos.toString().indexOf("error")==-1);
}
public void runIt() {
try {
Class params[] = {};
Object paramsObj[] = {};
Class thisClass = Class.forName(todayClass);
Object iClass = thisClass.newInstance();
Method thisMethod = thisClass.getDeclaredMethod("doit", params);
thisMethod.invoke(iClass, paramsObj);
}
catch (Exception e) {
e.printStackTrace();
}
}
}
It is possible to generate classes (via cglib, asm, javassist, bcel), but you shouldn't do it that way. Why?
the code that's using the library should expect type Object and get all the fields using reflection - not a good idea
java is statically typed language, and you want to introduce dynamic typing - it's not the place.
If you simply want the data in an undefined format, then you can return it in an array, like Object[], or Map<String, Object> if you want them named, and get it from there - it will save you much trouble with unneeded class generation for the only purpose of containing some data that will be obtained by reflection.
What you can do instead is have predefined classes that will hold the data, and pass them as arguments to querying methods. For example:
public <T> T executeQuery(Class<T> expectedResultClass,
String someArg, Object.. otherArgs) {..}
Thus you can use reflection on the passed expectedResultClass to create a new object of that type and populate it with the result of the query.
That said, I think you could use something existing, like an ORM framework (Hibernate, EclipseLink), spring's JdbcTemplate, etc.
This is possible, but (I believe) you need something like ASM or BCEL.
Alternately, you could use something with more power (like Groovy).
It will take a couple of minutes to create a data model class for each table, which you can easily map to the database with an ORM like Hibernate or by writing your own JDBC DAOs. It is far easier than delving deeply into reflection.
You could create a utility that interrogates the database structure for a table, and creates the data model class and DAO for you. Alternatively you could create the model in Java and create a utility to create the database schema and DAO from that (using reflection and Java 5 Annotations to assist). Don't forget that javaFieldNames are different from database_column_names typically.
Recently I needed to create about 200 simple classes from medatata (objects filled with static data) and I did it through the open source burningwave library, with the following scenario:
The classes needed to have a certain prefix in the name, for example "Registro "*.java;
The classes needed to extend from a superclass Registro.java
The classes needed to contain JPA annotations like #Entity, #Column (in attributes), Lombok annotations and custom annotations.
Here is the link to the repository with the complete project: https://github.com/leandrosoares6/criacao-classes-entidade-efd
Here is the code snippet responsible for creating the classes:
public class RegistrosClassFactory {
private static final String PACOTE = "com.example.demo.model.registros";
private static final String SCHEMA = "MY_SCHEMA";
private static final String PREFIXO = "Registro";
static void criaRegistros() {
List<RegistroTest> registros = RegistroMetadataFactory.criaMetadados();
criaClasses(registros);
}
private static void criaClasses(List<RegistroTest> registros) {
for (RegistroTest registroTest : registros) {
UnitSourceGenerator gerador = UnitSourceGenerator.create(PACOTE);
ClassSourceGenerator registro = ClassSourceGenerator
.create(TypeDeclarationSourceGenerator.create(PREFIXO + registroTest.getNome()))
.addModifier(Modifier.PUBLIC)
.addAnnotation(AnnotationSourceGenerator.create(Getter.class))
.addAnnotation(AnnotationSourceGenerator.create(Setter.class))
.addAnnotation(AnnotationSourceGenerator.create(NoArgsConstructor.class))
.addAnnotation(AnnotationSourceGenerator.create(ToString.class))
.addAnnotation(AnnotationSourceGenerator.create(Entity.class))
.addAnnotation(AnnotationSourceGenerator.create(Table.class)
.addParameter("name",
VariableSourceGenerator.create(String.format("\"%s\"",
registroTest.getNomeTabelaBd())))
.addParameter("schema", VariableSourceGenerator
.create(String.format("\"%s\"", SCHEMA))));
criaColunas(registroTest.getCampos(), registro);
registro.addConstructor(FunctionSourceGenerator.create().addModifier(Modifier.PUBLIC)
.addParameter(VariableSourceGenerator.create(String.class, "linha"))
.addBodyCodeLine("super(linha);")).expands(Registro.class);
gerador.addClass(registro);
// System.out.println("\nRegistro gerado:\n" + gerador.make());
String caminhoPastaRegistros = System.getProperty("user.dir") + "/src/main/java/";
gerador.storeToClassPath(caminhoPastaRegistros);
}
}
private static void criaColunas(List<Campo> campos, ClassSourceGenerator registro) {
for (Campo campo : campos) {
VariableSourceGenerator field = VariableSourceGenerator
.create(TypeDeclarationSourceGenerator.create(String.class),
campo.getNomeAtributo())
.addModifier(Modifier.PRIVATE)
.addAnnotation(AnnotationSourceGenerator.create(Column.class)
.addParameter("name", VariableSourceGenerator
.create(String.format("\"%s\"", campo.getNome())))
)
.addAnnotation(AnnotationSourceGenerator.create(Indice.class).addParameter(
"valor",
VariableSourceGenerator.create(String.valueOf(campo.getSequencial()))));
if (campo.getNome().equals("ID")) {
field.addAnnotation(AnnotationSourceGenerator.create(Id.class));
}
if (campo.getEId()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoId.class));
}
if (campo.getEData()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoData.class));
}
if (campo.getEDataPart()) {
field.addAnnotation(AnnotationSourceGenerator.create(CampoTipoDataPart.class));
}
registro.addField(field);
}
}
}
I'm aware of the performance drawback of reflection but for my little project I needed this and I created a project lib which converts JSON to Java and then finally .class in JVM context.
Anyone need such thing can have a look into my open source solution, which requires JDK to compile the code.
https://medium.com/#davutgrbz/the-need-history-c91c9d38ec9?sk=f076487e78a1ff5a66ef8eb1aa88f930

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