I have a Java application (an interpreter written in antlr4 to be precise) with numerous options in the code I would like to be [power] user configurable. Something like a config.properties file. Most of them are Boolean flags, if set, do this, else do that.
Currently, I have one class per flag, and the classes are scattered through-out the code, mostly in the same package where the implementation needs it. And, you can say:
import my.package.DoThis;
if (DoThis.isSet()) {
doThis();
} else {
doThat();
}
where the code for DoThis is something like
package my.package;
public class DoThis {
private static Boolean doThis = true; // the default
public static Boolean isSet() { return doThis; }
public static void set() { doThis = true; }
public static void clear() { doThis = false; }
}
And, there is a centralized part of the code that main calls, that initializes these options.
public void setup() {
DoThis.set();
DoAnother.clear();
if (cmd.option.debug()) { DoThird.set(); } else { DoThird.clear(): }
}
But, as I said, I'd like to clean the code up and use a configuration file that I can keep in the resources or a power user can override. A properties file or maybe a json file would seem like the right user interface.
However, properties read strings, do I check for yes/no, true/false? to set the flag. Or is there something better to do?
Should I also make all the options part of one class and perhaps store them in a map? What will make adding configuration options easiest?
Most importantly, I'd like to follow some form of Java best practices for doing so. I don't want to be that person who can write FORTRAN in any language. I want the code to look like what other Java programmers would naturally write. I'm pretty certain what I have now is not it.
I am not aware of a universally-accepted "best" approach for this. My preference would be not to have a separate class per flag, but rather to rather to centralise all the flags within a single class called, say, Config. It's public API might be something like the following (assuming the flags are called x, y and z):
public class Config {
private boolean x;
private boolean y;
private boolean z;
void setX(boolean value) { x = value; }
boolean getX() { return x; }
void setY(boolean value) { y = value; }
boolean getY() { return y; }
void setZ(boolean value) { z = value; }
boolean getZ() { return z; }
}
If you don't want to have to pass an instance of Config as a parameter to lots of different operations/constructors in your application, then you could create a singleton instance of Config.
I don't think my suggestion above would be too controversial among programmers. What is more likely to attract controversy is opinions about the "best" way to initialise the Config object. Some people might suggest that the Spring Framework should be used to inject values obtained from an XML file. Some other people might suggest that your setup() operation should read values from a configuration file in whatever happens to be your favourite syntax (properties, JSON, XML or whatever) and possibly allowing command-line options to override values specified in the configuration file
I am finding myself making a lot of Classes for use in GUI building (hence they must conform to the JavaBean pattern). This has created some issues for me regarding initialising. I often have some method that is quite time intensive that must be executed once the state has been set.
One approach is to document that the method init() must be executed and hope that people read and respect it, but that is clumsy and means that the GUIBuilder can't just be used as intended, but rather extra code has to be added.
I've checked Bloch's "Effective Java", these forums and of course I asked Dr Google, but I haven't come up with anything. To be fair, it's a bit of a wishy-washy set of search terms.
The following short example (obviously trivialised) demonstrates my current approach. I have an "isInitialised" variable and invalidate the instance whenever a setter is called. Whenever a getter is called on a calculated variable (or any other complicated method), the isInitialised variable is checked and if needed the init() method is called.
public class BeanTest {
private int someValue; // Just some number
private float anotherValue; // Just another number
private double calculatedValue; // Calculated by some expensive process
private boolean isInitialised = false; // Is calculatedValue valid?
/**
* Default constructor made available for JavaBean pattern
*/
public BeanTest() {
someValue = 0;
anotherValue = 0;
}
//******* Getters and setters follow ************/
public int getSomeValue() {
return someValue;
}
public void setSomeValue(int someValue) {
if (someValue == this.someValue) {
return;
}
isInitialised = false; // Calculated value is now invalid
this.someValue = someValue;
}
public float getAnotherValue() {
return anotherValue;
}
public void setAnotherValue(float anotherValue) {
if (anotherValue == this.anotherValue) {
return;
}
isInitialised = false; // Calculated value is now invalid
this.anotherValue = anotherValue;
}
/**
* This is where the time expensive stuff is done.
*/
public void init() {
if (isInitialised) {
return;
}
/* In reality this is some very costly process that I don't want to run often,
* probably run in another thread */
calculatedValue = someValue * anotherValue;
isInitialised = true;
}
/**
* Only valid if initialised
*/
public double getCalculatedValue() {
init();
return calculatedValue;
}
/**
* Code for testing
*/
public static void main(String[] args) {
BeanTest myBean = new BeanTest();
myBean.setSomeValue(3);
myBean.setAnotherValue(2);
System.out.println("Calculated value: " + myBean.getCalculatedValue());
}
}
This approach has multiple issues. For example, it doesn't extend well (and some of these really are intended to be extended). Also, I show only a simple case here with three variables; the real classes have many more. Things are becoming a mess.
Can anybody suggest a different method or pattern that could help me keep the code more elegant and readable and still allow things to work as expected in a GUI builder please?
P.S.
This is meant to be mutable.
EDITED
I think by trivialising I hid the point a bit.
The trick is I want to run the init() stuff only once, and only when everything is set. If I was using a builder pattern, this would be easy, as I would put it in the build() method, but this is in a GUI element and so is in a JavaBean pattern.
The code I have above is a trivialised version of the "pattern" I am using. The pattern does work, but there are many weaknesses as I have noted, particularly with extensability (is that a word?) and as the number of variables grows. The trivial example looks alright, but the real code is starting to look horrendous.
I guess this could just be a weakness of the JavaBean pattern, but I thought I'd ask before I crafted another dozen dodgy classes in my package.
Naive approach: why not simply call init() in the setter instead?
A bit more fancy: use a PropertyChangeSupport object. Sample usage:
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
public class TestBean implements PropertyChangeListener{
private int someValue;
private PropertyChangeSupport changeSupport;
public TestBean() {
changeSupport = new PropertyChangeSupport(this);
changeSupport.addPropertyChangeListener(this);
}
private void init() {
//do something time consuming, maybe even on a different thread, using Futures?
}
#Override
public void propertyChange(PropertyChangeEvent evt) {
init();
}
public int getSomeValue() {
return someValue;
}
public void setSomeValue(int someValue) {
int oldValue = this.someValue;
this.someValue = someValue;
changeSupport.firePropertyChange("someValue", oldValue, someValue);
}
}
I think I have to accept that what I'm trying to achieve can't be done. Here is a quote from Bloch's "Effective Java":
Unfortunately, the JavaBeans pattern has serious disadvantages of its
own. Because construction is split across multiple calls, a JavaBean
may be in an inconsistent state partway through its construction. The
class does not have the option of enforcing consistency merely by
checking the validity of the constructor parameters.
While it doesn't exactly answer my question, I think any answer that gets around the isInitialized variable would run into the issue that Bloch describes.
Request:
This is a very common problem faced by Java devs in my locale. I am really stuck for many days on this. Searched and tried a lot, read the docs. read ALL the stackoverflow questions related to JavaExe. Please only reply if you have done similar thing before and have a comprehensive answer. I would be really grateful to the community!
Senario:
I am using JavaExe to run an application as system service in desktop interactive capability.
To be exact I have an application that captures screenshots of desktops. I want it to run (as admin) on any user login so no one can stop it.
I have a myapp.jar, settings.txt and a lib dir.
I have searched alot and found JavaExe works (by watching its examples)
If anyone has a better way. Please state so.
Problem:
According to my research,
you must create a .properties file that has named like the .exe, and write "RunType = 1" in this file.
you define a static method in your main class : serviceInit()
Do I need to place any class or reference/import? How?
Edit:
My code below works as stand alone .jar and in javaExe.exe too.
It now does makes a system service and runs by as SYSTEM user. but It is NOT interactive to desktop. i.e its not showing any GUI.
package temp;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JOptionPane;
public class Temp {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
serviceInit();
}
public static boolean serviceInit(){
new Thread(){
public void run(){
Integer i = 0;
while(i < 999999999){
JOptionPane.showMessageDialog(null,i);
i++;
}
}
}.start();
return true;
}
}
And I dont think that bundling the .jar, lib directory and settings.txt into one .exe is possible?
you should have in your case :
public class MyApp_ServiceManagement
{
static boolean isMsgToDisplay = false;
/////////////////////////////
public static boolean serviceInit()
{
(new Thread()
{
public void run()
{
for(int i=0;i < 6;i++)
{
try { sleep(5*1000); }
catch(Exception ex) {}
isMsgToDisplay = true;
}
}
}).start();
return true;
}
/// is Data ready to be send to the UI ?
public static boolean serviceIsDataForUI()
{
return isMsgToDisplay;
}
/// Data to be send to the UI
public static Serializable serviceDataForUI()
{
isMsgToDisplay = false;
return "hello, I am an interactive Service";
}
}
and for the UI part :
public class MyApp_TaskbarManagement
{
/// To show (or not) the icon in tray
public static boolean taskIsShow()
{
return false;
}
/// Receive the message from Service
public static void taskDataFromService(Serializable data)
{
JOptionPane.showMessageDialog(null, data);
}
/// descr of UI
public static String[] taskGetInfo()
{
return new String[]
{
"UI part of Service"
};
}
}
the main() method is never called in service mode (except one particular case), but if you want keep your main() method you must put a call to main() in serviceInit().
Put serviceInit() in your main class or in another class named XXX_ServiceManagement where XXX is the name of your main class.
Then, serviceInit() must return before a 30 seconds delay.
Don't put a infinite loop, ... in it.
Put your code in a thread, and start it from serviceInit() (or main)
That answer to your problem?
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You can create various Java code templates in Eclipse via
Window > Preferences > Java > Editor > Templates
e.g.
sysout is expanded to:
System.out.println(${word_selection}${});${cursor}
You can activate this by typing sysout followed by CTRL+SPACE
What useful Java code templates do you currently use? Include the name and description of it and why it's awesome.
I am looking for an original/novel use of a template rather than a built-in existing feature.
Create Log4J logger
Get swt color from display
Syncexec - Eclipse Framework
Singleton Pattern/Enum Singleton Generation
Readfile
Const
Traceout
Format String
Comment Code Review
String format
Try Finally Lock
Message Format i18n and log
Equalsbuilder
Hashcodebuilder
Spring Object Injection
Create FileOutputStream
The following code templates will both create a logger and create the right imports, if needed.
SLF4J
${:import(org.slf4j.Logger,org.slf4j.LoggerFactory)}
private static final Logger LOG = LoggerFactory.getLogger(${enclosing_type}.class);
Log4J 2
${:import(org.apache.logging.log4j.LogManager,org.apache.logging.log4j.Logger)}
private static final Logger LOG = LogManager.getLogger(${enclosing_type}.class);
Log4J
${:import(org.apache.log4j.Logger)}
private static final Logger LOG = Logger.getLogger(${enclosing_type}.class);
Source.
JUL
${:import(java.util.logging.Logger)}
private static final Logger LOG = Logger.getLogger(${enclosing_type}.class.getName());
Some additional templates here: Link I -
Link II
I like this one:
readfile
${:import(java.io.BufferedReader,
java.io.FileNotFoundException,
java.io.FileReader,
java.io.IOException)}
BufferedReader in = null;
try {
in = new BufferedReader(new FileReader(${fileName}));
String line;
while ((line = in.readLine()) != null) {
${process}
}
}
catch (FileNotFoundException e) {
logger.error(e) ;
}
catch (IOException e) {
logger.error(e) ;
} finally {
if(in != null) in.close();
}
${cursor}
UPDATE: The Java 7 version of this template is:
${:import(java.nio.file.Files,
java.nio.file.Paths,
java.nio.charset.Charset,
java.io.IOException,
java.io.BufferedReader)}
try (BufferedReader in = Files.newBufferedReader(Paths.get(${fileName:var(String)}),
Charset.forName("UTF-8"))) {
String line = null;
while ((line = in.readLine()) != null) {
${cursor}
}
} catch (IOException e) {
// ${todo}: handle exception
}
Format a string
MessageFormat - surround the selection with a MessageFormat.
${:import(java.text.MessageFormat)}
MessageFormat.format(${word_selection}, ${cursor})
This lets me move a cursor to a string, expand the selection to the entire string (Shift-Alt-Up), then Ctrl-Space twice.
Lock the selection
lock - surround the selected lines with a try finally lock. Assume the presence of a lock variable.
${lock}.acquire();
try {
${line_selection}
${cursor}
} finally {
${lock}.release();
}
NB ${line_selection} templates show up in the Surround With menu (Alt-Shift-Z).
I know I am kicking a dead post, but wanted to share this for completion sake:
A correct version of singleton generation template, that overcomes the flawed double-checked locking design (discussed above and mentioned else where)
Singleton Creation Template:
Name this createsingleton
static enum Singleton {
INSTANCE;
private static final ${enclosing_type} singleton = new ${enclosing_type}();
public ${enclosing_type} getSingleton() {
return singleton;
}
}
${cursor}
To access singletons generated using above:
Singleton reference Template:
Name this getsingleton:
${type} ${newName} = ${type}.Singleton.INSTANCE.getSingleton();
Append code snippet to iterate over Map.entrySet():
Template:
${:import(java.util.Map.Entry)}
for (Entry<${keyType:argType(map, 0)}, ${valueType:argType(map, 1)}> ${entry} : ${map:var(java.util.Map)}.entrySet())
{
${keyType} ${key} = ${entry}.getKey();
${valueType} ${value} = ${entry}.getValue();
${cursor}
}
Generated Code:
for (Entry<String, String> entry : properties.entrySet())
{
String key = entry.getKey();
String value = entry.getValue();
|
}
For log, a helpful little ditty to add in the member variable.
private static Log log = LogFactory.getLog(${enclosing_type}.class);
Create a mock with Mockito (in "Java statements" context):
${:importStatic('org.mockito.Mockito.mock')}${Type} ${mockName} = mock(${Type}.class);
And in "Java type members":
${:import(org.mockito.Mock)}#Mock
${Type} ${mockName};
Mock a void method to throw an exception:
${:import(org.mockito.invocation.InvocationOnMock,org.mockito.stubbing.Answer)}
doThrow(${RuntimeException}.class).when(${mock:localVar}).${mockedMethod}(${args});
Mock a void method to do something:
${:import(org.mockito.invocation.InvocationOnMock,org.mockito.stubbing.Answer)}doAnswer(new Answer<Object>() {
public Object answer(InvocationOnMock invocation) throws Throwable {
Object arg1 = invocation.getArguments()[0];
return null;
}
}).when(${mock:localVar}).${mockedMethod}(${args});
Verify mocked method called exactly once:
${:importStatic(org.mockito.Mockito.verify,org.mockito.Mockito.times)}
verify(${mock:localVar}, times(1)).${mockMethod}(${args});
Verify mocked method is never invoked:
${:importStatic(org.mockito.Mockito.verify,org.mockito.Mockito.never)}verify(${mock:localVar}, never()).${mockMethod}(${args});
New linked list using Google Guava (and similar for hashset and hashmap):
${import:import(java.util.List,com.google.common.collect.Lists)}List<${T}> ${newName} = Lists.newLinkedList();
Also I use a huge template that generates a Test class. Here is a shortened fragment of it that everyone interested should customize:
package ${enclosing_package};
import org.junit.*;
import static org.junit.Assert.*;
import static org.hamcrest.Matchers.*;
import static org.mockito.Matchers.*;
import static org.mockito.Mockito.*;
import org.mockito.Mockito;
import org.slf4j.Logger;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;
import org.junit.runner.RunWith;
// TODO autogenerated test stub
#RunWith(MockitoJUnitRunner.class)
public class ${primary_type_name} {
#InjectMocks
protected ${testedType} ${testedInstance};
${cursor}
#Mock
protected Logger logger;
#Before
public void setup() throws Exception {
}
#Test
public void shouldXXX() throws Exception {
// given
// when
// TODO autogenerated method stub
// then
fail("Not implemented.");
}
}
// Here goes mockito+junit cheetsheet
Null Checks!
if( ${word_selection} != null ){
${cursor}
}
if( ${word_selection} == null ){
${cursor}
}
One of my beloved is foreach:
for (${iterable_type} ${iterable_element} : ${iterable}) {
${cursor}
}
And traceout, since I'm using it a lot for tracking:
System.out.println("${enclosing_type}.${enclosing_method}()");
I just thought about another one and have found it over the Internet some day, const:
private static final ${type} ${name} = new ${type} ${cursor};
A little tip on sysout -- I like to renamed it to "sop". Nothing else in the java libs starts with "sop" so you can quickly type "sop" and boom, it inserts.
Throw an IllegalArgumentException with variable in current scope (illarg):
throw new IllegalArgumentException(${var});
Better
throw new IllegalArgumentException("Invalid ${var} " + ${var});
Nothing fancy for code production - but quite useful for code reviews
I have my template coderev low/med/high do the following
/**
* Code Review: Low Importance
*
*
* TODO: Insert problem with code here
*
*/
And then in the Tasks view - will show me all of the code review comments I want to bring up during a meeting.
Some more templates here.
Includes:
Create a date object from a particular date
Create a new generic ArrayList
Logger setup
Log with specified level
Create a new generic HashMap
Iterate through a map, print the keys and values
Parse a time using SimpleDateFormat
Read a file line by line
Log and rethrow a caught exeption
Print execution time of a block of code
Create periodic Timer
Write a String to a file
slf4j Logging
${imp:import(org.slf4j.Logger,org.slf4j.LoggerFactory)}
private static final Logger LOGGER = LoggerFactory
.getLogger(${enclosing_type}.class);
Bean Property
private ${Type} ${property};
public ${Type} get${Property}() {
return ${property};
}
public void set${Property}(${Type} ${property}) {
${propertyChangeSupport}.firePropertyChange("${property}", this.${property}, this.${property} = ${property});
}
PropertyChangeSupport
private PropertyChangeSupport ${propertyChangeSupport} = new PropertyChangeSupport(this);${:import(java.beans.PropertyChangeSupport,java.beans.PropertyChangeListener)}
public void addPropertyChangeListener(PropertyChangeListener listener) {
${propertyChangeSupport}.addPropertyChangeListener(listener);
}
public void addPropertyChangeListener(String propertyName, PropertyChangeListener listener) {
${propertyChangeSupport}.addPropertyChangeListener(propertyName, listener);
}
public void removePropertyChangeListener(PropertyChangeListener listener) {
${propertyChangeSupport}.removePropertyChangeListener(listener);
}
public void removePropertyChangeListener(String propertyName, PropertyChangeListener listener) {
${propertyChangeSupport}.removePropertyChangeListener(propertyName, listener);
}
Post Java 7, a great way to set up loggers which need (or prefer) static references to the enclosing class is to use the newly introduced MethodHandles API to get the runtime class in a static context.
An example snippet for SLF4J is:
private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
Aside from being a simple snippet in any IDE, it is also less brittle if you refactor certain functionality into another class because you won't accidentally carry the class name with it.
Invoke code on the GUI thread
I bind the following template to the shortcut slater to quickly dispatch code on the GUI thread.
${:import(javax.swing.SwingUtilities)}
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
${cursor}
}
});
When testing around with code I sometimes missed out on deleting some syso s. So I made myself a template called syt.
System.out.println(${word_selection}${});//${todo}:remove${cursor}
Before I compile I always check my TODOs and will never forget to delete a System.out again.
strf -> String.format("msg", args) pretty simple but saves a bit of typing.
String.format("${cursor}",)
Get an SWT color from current display:
Display.getCurrent().getSystemColor(SWT.COLOR_${cursor})
Suround with syncexec
PlatformUI.getWorkbench().getDisplay().syncExec(new Runnable(){
public void run(){
${line_selection}${cursor}
}
});
Use the singleton design pattern:
/**
* The shared instance.
*/
private static ${enclosing_type} instance = new ${enclosing_type}();
/**
* Private constructor.
*/
private ${enclosing_type}() {
super();
}
/**
* Returns this shared instance.
*
* #returns The shared instance
*/
public static ${enclosing_type} getInstance() {
return instance;
}
And an equalsbuilder, hashcodebuilder adaptation:
${:import(org.apache.commons.lang.builder.EqualsBuilder,org.apache.commons.lang.builder.HashCodeBuilder)}
#Override
public boolean equals(Object obj) {
return EqualsBuilder.reflectionEquals(this, obj);
}
#Override
public int hashCode() {
return HashCodeBuilder.reflectionHashCode(this);
}
The template for the logger declaration is great.
I also create linfo, ldebug, lwarn, lerror for the log levels that I use more often.
lerror:
logger.error(${word_selection}${});${cursor}
Create everything for an event
Since events are kinda a pain to create in Java--all those interfaces, methods, and stuff to write just for 1 event--I made a simple template to create everything needed for 1 event.
${:import(java.util.List, java.util.LinkedList, java.util.EventListener, java.util.EventObject)}
private final List<${eventname}Listener> ${eventname}Listeners = new LinkedList<${eventname}Listener>();
public final void add${eventname}Listener(${eventname}Listener listener)
{
synchronized(${eventname}Listeners) {
${eventname}Listeners.add(listener);
}
}
public final void remove${eventname}Listener(${eventname}Listener listener)
{
synchronized(${eventname}Listeners) {
${eventname}Listeners.remove(listener);
}
}
private void raise${eventname}Event(${eventname}Args args)
{
synchronized(${eventname}Listeners) {
for(${eventname}Listener listener : ${eventname}Listeners)
listener.on${eventname}(args);
}
}
public interface ${eventname}Listener extends EventListener
{
public void on${eventname}(${eventname}Args args);
}
public class ${eventname}Args extends EventObject
{
public ${eventname}Args(Object source${cursor})
{
super(source);
}
}
If you have events that share a single EventObject, just delete the customized one inserted by the template and change the appropriate parts of raise___() and on____().
I had written a nice, little, elegant eventing mechanism using a generic interface and generic class, but it wouldn't work due to the way Java handles generics. =(
Edit:
1) I ran into the issue where threads were adding/removing listeners while an event was taking place. The List can't be modified while in use, so I added synchronized blocks where the list of listeners is being accessed or used, locking on the list itself.
Insert test methods should-given-when-then
I saw a similar version to this one recently while pair programming with a very good developer and friend, and I think it could be a nice addition to this list.
This template will create a new test method on a class, following the Given - When - Then approach from the behavior-driven development (BDD) paradigm on the comments, as a guide for structuring the code. It will start the method name with "should" and let you replace the rest of the dummy method name "CheckThisAndThat" with the best possible description of the test method responsibility. After filling the name, TAB will take you straight to the // Given section, so you can start typing your preconditions.
I have it mapped to the three letters "tst", with description "Test methods should-given-when-then" ;)
I hope you find it as useful as I did when I saw it:
#Test
public void should${CheckThisAndThat}() {
Assert.fail("Not yet implemented");
// Given
${cursor}
// When
// Then
}${:import(org.junit.Test, org.junit.Assert)}
Spring Injection
I know this is sort of late to the game, but here is one I use for Spring Injection in a class:
${:import(org.springframework.beans.factory.annotation.Autowired)}
private ${class_to_inject} ${var_name};
#Autowired
public void set${class_to_inject}(${class_to_inject} ${var_name}) {
this.${var_name} = ${var_name};
}
public ${class_to_inject} get${class_to_inject}() {
return this.${var_name};
}
Here is a constructor for non-instantiable classes:
// Suppress default constructor for noninstantiability
#SuppressWarnings("unused")
private ${enclosing_type}() {
throw new AssertionError();
}
This one is for custom exceptions:
/**
* ${cursor}TODO Auto-generated Exception
*/
public class ${Name}Exception extends Exception {
/**
* TODO Auto-generated Default Serial Version UID
*/
private static final long serialVersionUID = 1L;
/**
* #see Exception#Exception()
*/
public ${Name}Exception() {
super();
}
/**
* #see Exception#Exception(String)
*/
public ${Name}Exception(String message) {
super(message);
}
/**
* #see Exception#Exception(Throwable)
*/
public ${Name}Exception(Throwable cause) {
super(cause);
}
/**
* #see Exception#Exception(String, Throwable)
*/
public ${Name}Exception(String message, Throwable cause) {
super(message, cause);
}
}
I like a generated class comment like this:
/**
* I...
*
* $Id$
*/
The "I..." immediately encourages the developer to describe what the class does. I does seem to improve the problem of undocumented classes.
And of course the $Id$ is a useful CVS keyword.
I've had a lot of use of these snippets, looking for null values and empty strings.
I use the "argument test"-templates as the first code in my methods to check received arguments.
testNullArgument
if (${varName} == null) {
throw new NullPointerException(
"Illegal argument. The argument cannot be null: ${varName}");
}
You may want to change the exception message to fit your company's or project's standard. However, I do recommend having some message that includes the name of the offending argument. Otherwise the caller of your method will have to look in the code to understand what went wrong. (A NullPointerException with no message produces an exception with the fairly nonsensical message "null").
testNullOrEmptyStringArgument
if (${varName} == null) {
throw new NullPointerException(
"Illegal argument. The argument cannot be null: ${varName}");
}
${varName} = ${varName}.trim();
if (${varName}.isEmpty()) {
throw new IllegalArgumentException(
"Illegal argument. The argument cannot be an empty string: ${varName}");
}
You can also reuse the null checking template from above and implement this snippet to only check for empty strings. You would then use those two templates to produce the above code.
The above template, however, has the problem that if the in argument is final you will have to amend the produced code some (the ${varName} = ${varName}.trim() will fail).
If you use a lot of final arguments and want to check for empty strings but doesn't have to trim them as part of your code, you could go with this instead:
if (${varName} == null) {
throw new NullPointerException(
"Illegal argument. The argument cannot be null: ${varName}");
}
if (${varName}.trim().isEmpty()) {
throw new IllegalArgumentException(
"Illegal argument. The argument cannot be an empty string: ${varName}");
}
testNullFieldState
I also created some snippets for checking variables that is not sent as arguments (the big difference is the exception type, now being an IllegalStateException instead).
if (${varName} == null) {
throw new IllegalStateException(
"Illegal state. The variable or class field cannot be null: ${varName}");
}
testNullOrEmptyStringFieldState
if (${varName} == null) {
throw new IllegalStateException(
"Illegal state. The variable or class field cannot be null: ${varName}");
}
${varName} = ${varName}.trim();
if (${varName}.isEmpty()) {
throw new IllegalStateException(
"Illegal state. The variable or class field " +
"cannot be an empty string: ${varName}");
}
testArgument
This is a general template for testing a variable. It took me a few years to really learn to appreciate this one, now I use it a lot (in combination with the above templates of course!)
if (!(${varName} ${testExpression})) {
throw new IllegalArgumentException(
"Illegal argument. The argument ${varName} (" + ${varName} + ") " +
"did not pass the test: ${varName} ${testExpression}");
}
You enter a variable name or a condition that returns a value, followed by an operand ("==", "<", ">" etc) and another value or variable and if the test fails the resulting code will throw an IllegalArgumentException.
The reason for the slightly complicated if clause, with the whole expression wrapped in a "!()" is to make it possible to reuse the test condition in the exception message.
Perhaps it will confuse a colleague, but only if they have to look at the code, which they might not have to if you throw these kind of exceptions...
Here's an example with arrays:
public void copy(String[] from, String[] to) {
if (!(from.length == to.length)) {
throw new IllegalArgumentException(
"Illegal argument. The argument from.length (" +
from.length + ") " +
"did not pass the test: from.length == to.length");
}
}
You get this result by calling up the template, typing "from.length" [TAB] "== to.length".
The result is way funnier than an "ArrayIndexOutOfBoundsException" or similar and may actually give your users a chance to figure out the problem.
Enjoy!
I use this for MessageFormat (using Java 1.4). That way I am sure that I have no concatenations that are hard to extract when doing internationalization
i18n
String msg = "${message}";
Object[] params = {${params}};
MessageFormat.format(msg, params);
Also for logging:
log
if(logger.isDebugEnabled()){
String msg = "${message}"; //NLS-1
Object[] params = {${params}};
logger.debug(MessageFormat.format(msg, params));
}
My favorite few are...
1: Javadoc, to insert doc about the method being a Spring object injection method.
Method to set the <code>I${enclosing_type}</code> implementation that this class will use.
*
* #param ${enclosing_method_arguments}<code>I${enclosing_type}</code> instance
2: Debug window, to create a FileOutputStream and write the buffer's content's to a file.
Used for when you want to compare a buffer with a past run (using BeyondCompare), or if you can't view the contents of a buffer (via inspect) because its too large...
java.io.FileOutputStream fos = new java.io.FileOutputStream( new java.io.File("c:\\x.x"));
fos.write(buffer.toString().getBytes());
fos.flush();
fos.close();