I am using eclipse to develop a web application. Just today I have updated my struts version by changing the JAR file. I am getting warnings at some places that methods are deprecated, but the code is working fine.
I want to know some things
Is it wrong to use Deprecated methods or classes in Java?
What if I don't change any method and run my application with warnings that I have, will it create any performance issue.
1. Is it wrong to use Deprecated methods or classes in Java?
From the definition of deprecated:
A program element annotated #Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.
The method is kept in the API for backward compatibility for an unspecified period of time, and may in future releases be removed. That is, no, it's not wrong, but there is a better way of doing it, which is more robust against API changes.
2. What if I don't change any method and run my application with warnings that I have, will it create any performance issue.
Most likely no. It will continue to work as before the deprecation. The contract of the API method will not change. If some internal data structure changes in favor of a new, better method, there could be a performance impact, but it's quite unlikely.
The funniest deprecation in the Java API, is imo, the FontMetrics.getMaxDecent. Reason for deprecation: Spelling error.
Deprecated. As of JDK version 1.1.1, replaced by getMaxDescent().
You can still use deprecated code without performance being changed, but the whole point of deprecating a method/class is to let users know there's now a better way of using it, and that in a future release the deprecated code is likely to be removed.
Terminology
From the official Sun glossary:
deprecation: Refers to a class, interface, constructor, method or field that is no longer recommended, and may cease to exist in a future version.
From the how-and-when to deprecate guide:
You may have heard the term, "self-deprecating humor," or humor that minimizes the speaker's importance. A deprecated class or method is like that. It is no longer important. It is so unimportant, in fact, that you should no longer use it, since it has been superseded and may cease to exist in the future.
The #Deprecated annotation went a step further and warn of danger:
A program element annotated #Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists.
References
java.sun.com Glossary
Language guide/How and When to Deprecate APIs
Annotation Type Deprecated API
Right or wrong?
The question of whether it's right or wrong to use deprecated methods will have to be examined on individual basis. Here are ALL the quotes where the word "deprecated" appears in Effective Java 2nd Edition:
Item 7: Avoid finalizers: The only methods that claim to guarantee finalization are System.runFinalizersOnExit and its evil twin Runtime.runFinalizersOnExit. These methods are fatally flawed and have been deprecated.
Item 66: Synchronize access to shared mutable data: The libraries provide the Thread.stop method, but this method was deprecated long ago because it's inherently unsafe -- its use can result in data corruption.
Item 70: Document thread safety: The System.runFinalizersOnExit method is thread-hostile and has been deprecated.
Item 73: Avoid thread groups: They allow you to apply certain Thread primitives to a bunch of threads at once. Several of these primitives have been deprecated, and the remainder are infrequently used. [...] thread groups are obsolete.
So at least with all of the above methods, it's clearly wrong to use them, at least according to Josh Bloch.
With other methods, you'd have to consider the issues individually, and understand WHY they were deprecated, but generally speaking, when the decision to deprecate is justified, it will tend to lean toward wrong than right to continue using them.
Related questions
Difference between a Deprecated and Legacy API?
Aside from all the excellent responses above I found there is another reason to remove deprecated API calls.
Be researching why a call is deprecated I often find myself learning interesting things about the Java/the API/the Framework. There is often a good reason why a method is being deprecated and understanding these reasons leads to deeper insights.
So from a learning/growing perspective, it is also a worthwhile effort
It certainly doesn't create a performance issue -- deprecated means in the future it's likely that function won't be part of the library anymore, so you should avoid using it in new code and change your old code to stop using it, so you don't run into problems one day when you upgrade struts and find that function is no longer present
It's not wrong, it's just not recommended. It generally means that at this point there is a better way of doing things and you'd do good if you use the new improved way. Some deprecated stuff are really dangerous and should be avoided altogether. The new way can yield better performance than the deprecated one, but it's not always the case.
You may have heard the term, "self-deprecating humor". That is humor that minimizes your importance. A deprecated class or method is like that. It is no longer important. It is so unimportant, in fact, that it should no longer be used at all, as it will probably cease to exist in the future.
Try to avoid it
Generally no, it's not absolutely wrong to use deprecated methods as long as you have a good contingency plan to avoid any problems if/when those methods disappear from the library you're using. With Java API itself this never happens but with just about anything else it means that it's going to be removed. If you specifically plan not to upgrade (although you most likely should in the long run) your software's supporting libraries then there's no problem in using deprecated methods.
No.
Yes, it is wrong.
Deprecated methods or classes will be removed in future versions of Java and should not be used. In each case, there should be an alternative available. Use that.
There are a couple of cases when you have to use a deprecated class or method in order to meet a project goal. In this case, you really have no choice but to use it. Future versions of Java may break that code, but if it's a requirement you have to live with that. It probably isn't the first time you had to do something wrong in order to meet a project requirement, and it certainly won't be the last.
When you upgrade to a new version of Java or some other library, sometimes a method or a class you were using becomes deprecated. Deprecated methods are not supported, but shouldn't produce unexpected results. That doesn't mean that they won't, though, so switch your code ASAP.
The deprecation process is there to make sure that authors have enough time to change their code over from an old API to a new API. Make use of this time. Change your code over ASAP.
It is not wrong, but some of the deprecated methods are removed in the future versions of the software, so you will possibly end up with not working code.
Is it wrong to use Deprecated methods or classes in Java?"
Not wrong as such but it can save you some trouble. Here is an example where it's strongly discouraged to use a deprecated method:
http://java.sun.com/j2se/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html
Why is Thread.stop deprecated?
Because it is inherently unsafe.
Stopping a thread causes it to unlock
all the monitors that it has locked.
(The monitors are unlocked as the
ThreadDeath exception propagates up
the stack.) If any of the objects
previously protected by these monitors
were in an inconsistent state, other
threads may now view these objects in
an inconsistent state. Such objects
are said to be damaged. When threads
operate on damaged objects, arbitrary
behavior can result. This behavior may
be subtle and difficult to detect, or
it may be pronounced. Unlike other
unchecked exceptions, ThreadDeath
kills threads silently; thus, the user
has no warning that his program may be
corrupted. The corruption can manifest
itself at any time after the actual
damage occurs, even hours or days in
the future.
What if don't change any method and run my application with warnings that I have, will it create any performance issue.
There should be no issues in terms of performance. The standard API is designed to respect some backward compatibility so applications can be gradually adapted to newer versions of Java.
Is it wrong to use Deprecated methods or classes in Java?
It is not "wrong", still working but avoid it as much as possible.
Suppose there is a security vulnerability associated with a method and the developers determine that it is a design flaw. So they may decide to deprecate the method and introduce the new way.
So if you still use the old method, you have a threat. So be aware of the reason to the deprecation and check whether how it affects to you.
what if don't change any method and run my application with warnings that I have, will it create any performance issue.
If the deprecation is due to a performance issue, then you will suffer from a performance issue, otherwise there is no reason to have such a problem. Again would like to point out, be aware of the reason to deprecation.
In Java it's #Deprecated, in C# it's [Obsolete].
I think I prefer C#'s terminology. It just means it's obsolete. You can still use it if you want to, but there's probably a better way.
It's like using Windows 3.1 instead of Windows 7 if you believe that Windows 3.1 is obsolete. You can still use it, but there's probably better features in a future version, plus the future versions will probably be supported - the obsolete one won't be.
Same for Java's #Deprecated - you can still use the method, but at your own risk - in future, it might have better alternatives, and might not even be supported.
If you are using code that is deprecated, it's usually fine, as long as you don't have to upgrade to a newer API - the deprecated code might not exist there. I suggest if you see something that is using deprecated code, to update to use the newer alternatives (this is usually pointed out on the annotation or in a Javadoc deprecated comment).
Edit: And as pointed out by Michael, if the reason for deprecation is due to a flaw in the functionality (or because the functionality should not even exist), then obviously, one shouldn't use the deprecated code.
Of course not - since the whole Java is getting #Deprecated :-) you can feel free to use them for as long as Java lasts. Not going to notice any diff anyway, unless it's something really broken. Meaning - have to read about it and then decide.
In .Net however, when something is declared [Obsolete], go and read about it immediately even if you never used it before - you have about 50% chance that it's more efficient and/or easier to use than replacement :-))
So in general, it can be quite beneficial to be techno-conservative these days, but you have to do your reading chore first.
I feel that deprecated method means; there is an alternate=ive method available which is better in all aspects than existing method. Better to use the good method than existing old method. For backward compatibility, old methods are left as deprecated.
I read here that using the old mysql-functions is not recommended anymore. But is it of any use to make the effort to update the code in an already finshed and running project so only mysqli-functionality is used?
What would be the benefits?
What security issues would be enhanced?
If you have you security all right in the current project, it wouldn't be enhanced then.
Though, it is extremely common habit of PHP users to confuse security measures, so, you have to double-check. Say, if you're using a home-brewed version of magic quotes, by escaping all input parameters - you're in danger.
You need to audit the security despite of changing drivers though.
And you can achieve them without moving to mysqli, though.
As of benefits - there are none, compared to all the pains of rewriting.
If you're still in the mood of rewriting, I have a suggestion:
Instead of just rewriting from one raw API to another, let me suggest you to adopt some database abstraction library, moving raw API calls from all of your code into one compact place.
It will not only make your code dramatically shorter, but also will help in the future, when someone will have a whim to deprecate mysqli in turn - you will have to rewrite your class' methods only, not all the code.
The primary benefits you would gain from upgrading to the PHP mysqli extension are definitively listed on that page:
The mysqli extension has a number of benefits, the key enhancements over the mysql extension being:
Object-oriented interface
Support for Prepared Statements
Support for Multiple Statements
Support for Transactions
Enhanced debugging capabilities
Embedded server support
Security enhancements would generally not be discussed on public forums due to the potential for malicious individuals to use those security concerns on older, unpatched servers. Suffice to say that there are always improvements in new code, especially a driver called the MySQL improved extension.
On my website I use both a postgresql and mysql database
I want to convert to PDO as I have been informed that PHP will be removing the old mysql_ functions soon and I assume this means the pg_ functions will disappear as well.
I only ever use:
pg_connect/mysql_connect & mysql_select_db
pg_query/mysql_query
pg_result/mysql_result
pg_numrows/mysql_numrows (for checking if there is a result, or looping through resultset)
pg_fetch_array
I have thousands of queries and don't relish the idea of going through every one.
Is it possible just to go through and make global changes in my code to implement PDO?
Does that mean I can just do a global change mysql=mysqli in the interim?
Well the answer is somewhat complex and can be divided into 2 parts.
Let's look into the question first:
There are actually 2 possible reasons to change your codes.
Deprecation process for mysql extension.
Making your code safer against SQL injection.
For the first one, it is not actually an urgent reason.
It will be deprecated in the not-released-yet version and removed in not-even-known version. So, to hit whatever trouble you will need to have a PHP version with removed mysql support. According to my experience, new versions moves on the shared hosts slowly, and you have 7 to 10 years ahead.
For the second reason, simple bulk search and replace will do no good at all.
So, instead of going for this option in a hurry, I'd go for gradual refactoring, eventually replacing old code with better versions.
This question already has answers here:
Why shouldn't I use mysql_* functions in PHP?
(14 answers)
Closed 9 years ago.
When I attempt to connect to a MySQL server from PHP, I see the following error:
Deprecated: The mysql extension is deprecated and will be removed in the future: use mysqli or PDO instead in /path/to/filename.php on line 123
The code on the referenced line is:
mysql_connect($server, $username, $password);
I am certain that the arguments are correct, and this exact code has been working for years without problem. Indeed, I obtained it from a well-sourced tutorial on PHP.
Why is this happening?
How can I fix it?
I understand that it's possible to suppress deprecation errors by setting error_reporting in php.ini to exclude E_DEPRECATED:
error_reporting = E_ALL ^ E_DEPRECATED
What will happen if I do that?
Why is this happening?
The entire ext/mysql PHP extension, which provides all functions named with the prefix mysql_, was officially deprecated in PHP v5.5.0 and removed in PHP v7.
It was originally introduced in PHP v2.0 (November 1997) for MySQL v3.20, and no new features have been added since 2006. Coupled with the lack of new features are difficulties in maintaining such old code amidst complex security vulnerabilities.
The manual has contained warnings against its use in new code since June 2011.
How can I fix it?
As the error message suggests, there are two other MySQL extensions that you can consider: MySQLi and PDO_MySQL, either of which can be used instead of ext/mysql. Both have been in PHP core since v5.0, so if you're using a version that is throwing these deprecation errors then you can almost certainly just start using them right away—i.e. without any installation effort.
They differ slightly, but offer a number of advantages over the old extension including API support for transactions, stored procedures and prepared statements (thereby providing the best way to defeat SQL injection attacks). PHP developer Ulf Wendel has written a thorough comparison of the features.
Hashphp.org has an excellent tutorial on migrating from ext/mysql to PDO.
I understand that it's possible to suppress deprecation errors by setting error_reporting in php.ini to exclude E_DEPRECATED:
error_reporting = E_ALL ^ E_DEPRECATED
What will happen if I do that?
Yes, it is possible to suppress such error messages and continue using the old ext/mysql extension for the time being. But you really shouldn't do this—this is a final warning from the developers that the extension may not be bundled with future versions of PHP (indeed, as already mentioned, it has been removed from PHP v7). Instead, you should take this opportunity to migrate your application now, before it's too late.
Note also that this technique will suppress all E_DEPRECATED messages, not just those to do with the ext/mysql extension: therefore you may be unaware of other upcoming changes to PHP that would affect your application code. It is, of course, possible to only suppress errors that arise on the expression at issue by using PHP's error control operator—i.e. prepending the relevant line with #—however this will suppress all errors raised by that expression, not just E_DEPRECATED ones.
What should you do?
You are starting a new project.
There is absolutely no reason to use ext/mysql—choose one of the other, more modern, extensions instead and reap the rewards of the benefits they offer.
You have (your own) legacy codebase that currently depends upon ext/mysql.
It would be wise to perform regression testing: you really shouldn't be changing anything (especially upgrading PHP) until you have identified all of the potential areas of impact, planned around each of them and then thoroughly tested your solution in a staging environment.
Following good coding practice, your application was developed in a loosely integrated/modular fashion and the database access methods are all self-contained in one place that can easily be swapped out for one of the new extensions.
Spend half an hour rewriting this module to use one of the other, more modern, extensions; test thoroughly. You can later introduce further refinements to reap the rewards of the benefits they offer.
The database access methods are scattered all over the place and cannot easily be swapped out for one of the new extensions.
Consider whether you really need to upgrade to PHP v5.5 at this time.
You should begin planning to replace ext/mysql with one of the other, more modern, extensions in order that you can reap the rewards of the benefits they offer; you might also use it as an opportunity to refactor your database access methods into a more modular structure.
However, if you have an urgent need to upgrade PHP right away, you might consider suppressing deprecation errors for the time being: but first be sure to identify any other deprecation errors that are also being thrown.
You are using a third party project that depends upon ext/mysql.
Consider whether you really need to upgrade to PHP v5.5 at this time.
Check whether the developer has released any fixes, workarounds or guidance in relation to this specific issue; or, if not, pressure them to do so by bringing this matter to their attention. If you have an urgent need to upgrade PHP right away, you might consider suppressing deprecation errors for the time being: but first be sure to identify any other deprecation errors that are also being thrown.
It is absolutely essential to perform regression testing.
I saw this tutorial for writing a JSON-RPC server for SWI-Prolog. Unfortunately, all it does is add two numbers. I'm wondering if there exists a RPC server for SWI-Prolog that can define new rules and answer general Prolog queries, returning JSON lists, etc?
When you take a tour on SWI-Prolog website, proudly self-powered, you can see at work some of the features offered by http package.
It's a fairly large range of tools, and to grasp the basic of the system, the easiest way it's to follow the specific How to section, step by step. There is a small bug you should be aware in the LOD Crawler: add an option on line 42 of lod.pl:
...
; rdf_load(URI2, [format(xml)]),
....
or you will probably get
Internal server error
Domain error: content_type' expected, found text/xml;charset=UTF-8'
when running the sample.
An important feature of the IDE it's the ability to debug the HTTP requests.
When done with the HowTo, you can take a look to Cliopatria, dedicated to interfacing RDF to HTML. It come with a pirates demo, I must say I find it a bit too 'crude' for my taste, and I don't know about YUI, used in the award winning MultimediaN project. Then I've used Bootstrap to gain a modern look for the front end, with appreciable result (I'm sorry I can't - yet - publish it, need more time to engineering the system).
HTH