Simply call pageContext.setAttribute() to export a variable from within a JSP custom tag: public class MyCustomVarTag extends TagSupport { ... The availability of the exported variable can be limited in the TLD: <tag> <name>setVar</name> <tag-class... The availability scopes are: Value Availability NESTED Between the start tag and the end tag. AT_BEGIN From the start tag until the scope of any enclosing tag. If there’s no enclosing tag, then to the end of the page. AT_END After the end tag until the scope of any enclosing tag. If there’s no enclosing tag, then to the end of the page.

This is an HTML image tag filter using Java regex. It takes a string, finds the img tags, replaces the src attribute with one provided by the filter, then adds a class name to the class attribute. import java.util.regex.*; import java.io.*; ... Test file: <div id="HTML snippet"> <img src="img/big/txt-m...

Some methods to search for a substring within a string: To know that a substring indeed exists within a string: boolean found = wholeString.contains(substring); To find where the substring is contained: int index = wholeString.indexOf(substring); If the substring is regex: boolean match = wholeString.matches(".*" + substri... Case insensitive match: convert both whole string and substring to lowercase, then compare. Or, use case insensitive flag for regex. Test code: import java.util.regex.*; public class Stri...

This is a simple doclet that prints all public methods and their parameter names and types. Code import com.sun.javadoc.*; public class List... Compile javac -cp $JAVA_HOME/lib/tools.jar:. ListMethodsDo... Use javadoc -doclet ListMethodsDoclet -sourcepath /pat...

This is an example that uses dynamic proxies to trace method calls (in logging) and print out elapsed times for them. Because dynamic proxies can only be generated for interfaces, the service classes must be implemented with interface-implementation pairs. Create services A and B. A.java : public interface A { public void service1()... AImpl.java : import java.util.Random; public class AImpl... B.java : public interface B { public void service1()... BImpl.java : public class BImpl implements B { public vo... The call trace proxy: import java.lang.reflect.*; class TraceProx... The performance proxy: import java.lang.reflect.*; class Performan... The service factory: import java.lang.reflect.*; public class Se... The test class: public class Test { public static void main... The output: Entering AImpl.service1 Entering BImpl.service1... The above example has no information...

Dynamic proxy can be used to eliminate the need to stub out unused interface methods. This is an example for a simple SAX content handler for XML parsing. The org.xml.sax.ContentHandler interface requires 11 methods be implemented but we only need three: import java.io.IOException; import java.util.Ar... With a dynamic proxy, we don't need the empty blocks for the unused methods: import java.io.IOException; import java.util.Ar... Equivalently (with anonymous inner class): import java.io.IOException; import java.util.Ar... demo.xml : <breakfast-menu> <food> <name>Belgian W...

This is an odd-ball content provider in that it doesn't provide database records, but provides a resource as a stream. It can be used to provide media files or XML resources. Start the project with: tools/android create project --package com.android... Create assets directory and add an XML file ( assets/demo.xml ): <? xml version="1.0" encoding="UTF-8"?> <people... Edit the layout ( res/layout/main.xml ): <?xml version="1.0" encoding="utf-8"?> <LinearL... Edit src/com/android/cptest/Dummy.java : package com.android.cptest; import java.io.... Add content provider ( src/com/android/cptest/XmlResource.java ): package com.android.cptest; import java.io.... Update AndroidManifest.xml : <?xml version="1.0" encoding="utf-8"?> <manifes... Add this section to the end of build.xml : <target name="-package-resources"> <ech... Build and install: ant install Screenshot: Remove the Dummy activity ( AndroidManifest.xml ): <?xml version="1.0" encoding="utf-8"?> <manifes... Create a new project for...

Create new project $ tools/android create project \ > --package co... Edit res/values/string.xml , add strings for the main screen. <?xml version="1.0" encoding="utf-8"?> <resourc... Add widgets to main layout ( res/layout/main.xml ). <?xml version="1.0" encoding="utf-8"?> <LinearL... Edit src/com/android/apkinfo/GetAPKPermissions.java and change contents to: package com.android.apkinfo; import android... Install the debug package to the emulator: ant install The screen should look like: Add display permissions activity. Start by creating a new layout res/layout/display_permissions.xml : <?xml version="1.0" encoding="utf-8"?> <LinearL... Add the strings used by the new Activity ( res/values/strings.xml ): <?xml version="1.0" encoding="utf-8"?> <resourc... Add the Display Permissions Activity ( src/com/android/apkinfo/DisplayPermissions.java ): package com.android.apkinfo; import android... Change src/com/android/apkinfo/GetAPKPermissions.java to invoke the Display Permissions Activity: package com.android.apkinfo; import android... Declare Display Permissions Activity in AndroidManifest.xml : <?xml version="1.0" encoding="utf-8"?> <manifes......

The Java Executor interface replaces the call new Thread(new RunnableTask()).start() with executor.execute(new RunnableTask()) . The concurrent package provides built-in utility classes to manage threads so that you don't need to worry about them. import java.util.concurrent.TimeUnit; import ja...

The java.util.concurrent.atomic package is a small toolkit of classes that support lock-free thread-safe programming on single variables . This is an example of a shared counter without synchronization or lock: import java.util.concurrent.atomic.AtomicInteger; ...