Java属性：.properties文件vs xml？

Question

I'm a newbie when it comes to properties, and I read that XML is the preferred way to store these. I noticed however, that writing a regular .properties file in the style of

foo=bar
fu=baz

also works. This would mean a lot less typing (and maybe easier to read and more efficient as well). So what are the benefits of using an XML file?

Answer 1

In XML you can store more complex (eg hierarchical) data than in a properties file. So it depends on your usecase. If you just want to store a small number of direct properties a properties file is easier to handle (though the Java properties class can read XML based properties, too).

It would make sense to keep your configuration interface as generic as possible anyway, so you have no problem to switch to another representation ( eg by using Apache Commons Configuration ) if you need to.

Answer 2

The biggest benefit to using an XML file is that XML declares its encoding, while .properties does not.

If you are translating these properties files to N languages, it is possible that these files could come back in N different encodings. And if you're not careful, you or someone else could irreversibly corrupt the character encodings.

Answer 3

If you have a lot of repeating data, it can be simpler to process

<connections>
  <connection>this</connection>
  <connection>that</connection>
  <connection>the other</connection>
</connections>

than it is to process

connection1=this
connection2=that
connection3=the other

especially if you are expecting to have to store a lot of data, or it must be stored in a definite hierarchy

If you are just storing a few scalar values though, I'd go for the simple Properties approach every time

Answer 4

If you have both hierarchical data & duplicate namespaces, then use XML.

1) To emulate just a hierarchical structure in a properties file, simply use dot notation:

a.b=The Joker
a.b.c=Batgirl
a.b=Batman
a.b=Superman
a.b.c=Supergirl

So, complex (hierarchical) data representation is *not a reason to use xml.

2) For just repeating data, we can use a 3rd party library like ini4j to peg explicitly in java a count identifier on an implicit quantifier in the properties file itself.

a.b=The Joker
a.b=Batgirl
a.b=Batman

is translated to (in the background)

a.b1=The Joker
a.b2=Batgirl
a.b3=Batman

However, numerating same name properties still doesn't maintain the specific parent-child relationships. ie. how do we represent whether Batgirl is with The Joker or Batman?

So, xml is required when both features are needed. We can now decide if the 1st xml entry is what we want or the 2nd.

[a]
   [b]Joker[/b]
   [b]
       [c]Batgirl[/c]
   [/b]
[a]

--or--

[a]
   [b]Batman[/b]
   [b]
       [c]Batgirl[/c]
   [/b]
[/a]

Further detail in .... http://ilupper.blogspot.com/2010/05/xml-vs-properties.html

Answer 5

XML is handy for complex data structures and or relationships. It does a decent job for having a "common language" between systems.

However, xml comes at a cost. Its is heavy to consume. You've got to load a parser, ensure the file is in the correct format, find the information etc...

Whereas properties files is pretty light weight and easy to read. Works for simple key/value pairs.

Answer 6

It depends on the data you're encoding. With XML, you can define a more complex representation of the configuration data in your application. Take something like the struts framework as an example. Within the framework you have a number of Action classes that can contain 1...n number of forward branches. With an XML configuration file, you can define it like:

<action class="MyActionClass">
  <forward name="prev" targetAction="..."/>
  <forward name="next" targetAction="..."/>
  <forward name="help" targetAction="..."/>
</action>

This kind of association is difficult to accomplish using just the key-value pair representation of the properties file. Most likely, you would need to come up with a delimiting character and then include all of the forward actions on a single property separated by this delimiting character. It's quite a bit of work for a hackish solution.

Yet, as you pointed out, the XML syntax can become a burden if you just want to state something very simple, like set feature blah to true.

Answer 7

The disadvantages of XML:

1. It is hard to read - the tags make it look busier than it really is
2. The hierarchies and tags make it hard to edit and more prone to human errors
3. It is not possible to "append" to an XML property file to introduce a new property or provide an overriding value for an existing property so that the last one wins. The ability to append a property can be very powerful - we can implement a property management logic around this so that certain properties are "hot" and we don't need to restart the instance when these change

The Java property file solves the above problems. Consistent naming conventions and dot notation can help in solving the issue of hierarchy.