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Created by Dr. Xi on June 22, 2011 15:15:15    Last update: June 22, 2011 15:15:15
There's no such thing as an immutable byte array in Java. What we are trying to achieve here is to protect the byte array inside the object from which it is being returned. We want to caller to have the contents of the byte array, but not be able to change the contents inside the object. The trick is to return a copy instead of the internal reference: public class ReturnByteArray { public stati...
Created by alfa on June 02, 2011 15:49:26    Last update: June 02, 2011 15:51:08
Facts: Dynamic proxy classes are generated by the Java runtime, from a list of interfaces given by the user. The generated proxy class implements all interfaces given by the user. The dynamic proxy class is not synthetic . The dynamic proxy class is useless without a user supplied InvocationHandler class, since there's only one constructor for the proxy class and it takes a InvocationHandler as parameter. Example code: import java.lang.reflect.Constructor; import ja... Output: Class: $Proxy0 isSynthetic: false Constructo...
Created by alfa on June 02, 2011 15:26:37    Last update: June 02, 2011 15:26:37
While doing some Java reflection code, I noticed the method Class.isSynthetic() , which the JavaDoc says returns " true if and only if this class is a synthetic class as defined by the Java Language Specification". However, there's no definition of "synthetic class" in the JLS ! The only thing that I can find that remotely resembles a definition is in the JVM spec , where it defines the synthetic attribute : "The Synthetic attribute is a fixed-length attribute in the attributes table of ClassFile (§4.1), field_info (§4.5), and method_info (§4.6) structures. A class member that does not appear in the source code must be marked using a Synthetic attribute." By this definition, a default constructor, which does not appear in the source code, should...
Created by Dr. Xi on October 26, 2010 16:07:40    Last update: October 26, 2010 16:07:40
This is a more generic version, which can be expanded to accommodate additional file signatures. import java.io.*; import java.util.*; pu...
Created by Dr. Xi on August 03, 2010 16:23:55    Last update: October 22, 2010 15:35:20
According to Java documentation: The Java compiler and other Java tools can only process files which contain Latin-1 and/or Unicode-encoded (\udddd notation) characters. This utility converts a utf-8 encoded file to ascii with unicode escape strings for non-ascii characters. import java.io.*; /** * Reads file in U... It is equivalent to: native2ascii -encoding utf-8 using the standard Java native2ascii utility.
Created by Dr. Xi on July 19, 2010 21:58:34    Last update: July 23, 2010 21:37:23
Parsing XML in Java is really simple: import java.io.*; import javax.xml.parsers.Docu... The parser implementation details are hidden behind the JAXP API. In case you want to know which parser implementation is used, this is what the JavaDoc for DocumentBuilderFactory.newInstance says: Use the javax.xml.parsers.DocumentBuilderFactory system property. Use the properties file " lib/jaxp.properties " in the JRE directory. This configuration file is in standard java.util.Properties format and contains the fully qualified name of the implementation class with the key being the system property defined above. The jaxp.properties file is read only once by the JAXP implementation and it's values are then cached for future use. If the file does not exist when the first attempt is made to read from it, no further attempts are made to...
Created by Dr. Xi on June 20, 2010 14:35:17    Last update: June 20, 2010 14:35:17
This XML signature validator comes from the Apache XML Security project. It validates the signature according to the core validation processing rules . It does not verify that the key used to generate the signature is a trusted key. You can override the KeySelector class to make sure that the signing key is from a trusted store. import javax.xml.crypto.*; import javax.xml.cry...
Created by Dr. Xi on June 11, 2010 23:11:59    Last update: June 11, 2010 23:14:02
Given a simple XML file like this: <?xml version="1.0"?> <root id="1"> ... Calling Document.getElementById returns null (surprisingly!): import java.io.*; import org.w3c.dom.*; impo... In fact the JavaDoc says something along the lines that getElementById returns the Element that has an ID attribute with the given value. An attribute with the name "ID" or "id" is not of type ID unless it is so defined. How is an attribute defined as an ID attribute ? With a DTD or schema. If you are not validating the XML, then the API is useless. So, what to do if you want to find an element for which the attribute named "id" has a given value? Several options were offered in GetElementById Pitfalls . One of them is to...
Created by Dr. Xi on February 09, 2009 23:14:15    Last update: February 09, 2009 23:14:15
This example demonstrates the general steps in creating a custom Java class loader. Normally a class loader would consult its parent class loader when asked to load a class. If it's not loaded by the parent class loader, then the class loader would try to load the class on its own. This class loader tries to load the requested class on its own first, and delegates to the parent only when a java.lang.SecurityException is thrown (which happens when it tries to load core Java classes such as java.lang.String ). The classes are loaded from CLASSPATH through the getResourceAsStream call. It's important to note that when a class is loaded with a certain class loader, all classes referenced from that class are also loaded through the...
Created by Dr. Xi on September 25, 2008 02:58:27    Last update: October 14, 2008 22:49:32
This following code came from a JavaWorld tip, with some minor modifications. public class JWhich { /** * Retu...