Groovy: Writing objects without Serializable

Problem Summary

You want to serialize an object to a file, but it doesn’t implement Serializable.

class User{
    String name;
    String phone;
    String favoriteColor;
}

The Serializable interface is annoying. It’s a basic object. Just let me read/write the object!!

JSON Proposal

One solution is very straightforward - don’t use proper “Serialization” - because it may not actually be what you need. The downside to this is that == is not satisfied, but you probably do not need this!

Here’s a basic example using Groovy’s helpful JsonOutput and JsonSlurper classes.

def testUser = new User(
    name: 'steven',
    phone: '1-770-555-1212',
    favoriteColor: 'red'
)

//convert to json
def testUserJson = JsonOutput.toJson(testUser)

//write to file
def outputFile = new File("testUser.json")
outputFile.write(testUserJson)

//read object from file
def testUser2 = JsonSlurper.parse(outputFile) as User

Cache implemenation using this approach

I added an implementation of the Grails Cache Plugin that uses this approach here: Grails Filesystem Cache Plugin

This had the added complexity of dynamic file names. Given arbitrary key types, and filename length limitations, I used SHA256(json(key)).json for the filename.