Question

I’m working on a program where I want to output to a file that has the current data in yyy/MM/dd format appended to the filename.

I want to inject the File object representing the output file location into the class that needs it using Spring.

However, I don’t know how to append the current date to the filename argument when creating the File object.

In actual code it’s easy:

String outputFileName = "someFile";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
outputFileName += " " + sdf.format(new Date());
File outputFile = new File(outputFileName);

How can I do this in my Spring bean configuration file?

Is it even possible to do this, and if so how could I go about it?

Answer 1

Well… technically you can do almost everything. I’m using FastDateFormat because it’s both fast (duh!) and thread-safe. java.text.SimpleDateFormat can be used as well:

<bean id="fastDateFormat" class="org.apache.commons.lang.time.FastDateFormat" factory-method="getInstance">
    <constructor-arg value="yyyy/MM/dd"/>
</bean>

<bean id="currentDate" class="java.util.Date" factory-bean="fastDateFormat" factory-method="format">
    <constructor-arg>
        <bean class="java.util.Date"/>
    </constructor-arg>
</bean>

And then simply inject:

@Resource
private String currentDate;  //2011/12/13

Note that it would be much simpler to run it in plain Java or using @Configuration approach:

@Bean FastDateFormat fastDateFormat() {
  return new FastDateFormat("yyyy/MM/dd");
}

@Bean String currentDate() = {
  return fastDateFormat().format(new Date());
}

That being said, why don’t you just write it plain Java in @PostConstruct rather than over-relying on DI? Not everything has to be injected… The only advantage is that it makes testing easier since you can inject fake string and do not rely on current date. But in this case think of some DateProvider interface, makes life simpler.

Also do you really want to have the same date for the whole application lifetime (it will be generated once at startup)? If not, currentDate bean must have prototype scope and you must lazily fetch it from the container every time you need it…