Recently, I was looking for a new apartment in New York. It’s obvious that the first place where you need to start looking for something is craigslist. I didn’t find any way to receive emails when somebody posts a new ad which has specific keywords and matches my filters. I decided to write a small script which could solve this problem. I’ve had some experience with groovy and wanted to refresh my memory.

##Let’s get it started

What we need? Not so long ago I began to choose gradle for each project. This’s not an exception too.

apply plugin: 'groovy'
apply plugin: 'application'

mainClassName = "com.dimafeng.craigslist.Main"

sourceCompatibility = 1.5
version = '1.0'

repositories {
mavenCentral()
}

dependencies {
compile 'org.codehaus.groovy:groovy-all:2.3.9'
compile 'org.jsoup:jsoup:1.8.1'
compile 'javax.mail:mail:1.4.7'
testCompile group: 'junit', name: 'junit', version: '4.11'
}

task uberjar(type: Jar, dependsOn: build) {
from files(sourceSets.main.output.classesDir)
from {configurations.compile.collect {zipTree(it)}}

manifest {
attributes 'Main-Class': 'com.dimafeng.craigslist.Main'
}
}

This build script is pretty simple. I added application plugin just for testing, you don’t really need it. As for dependencies - we need:

  • groovy is needed for project compilation
  • jsoup is good lib for html DOM manipulations in JQuery style
  • javax.mail is simplest way to email sending

Let’s write some groovy code.

public static void main(String[] args) {

println "App started " + new Date()

//Reading file with old ads
def old = new ArrayList()
def file = new File('old')
def firstStart = false
if (!file.exists()) {
file.createNewFile();
firstStart = true;
} else {
old.addAll(file.readLines())
}

//Config parsing
def config = new Properties()
config.load(new File('app.properties').newDataInputStream())

def targetUrl = config.getProperty("app.url")
def baseUrl = targetUrl.replaceAll("(http://(.*?).craigslist.org)(.*)", '$1');

Document doc = Jsoup.connect(targetUrl).get();
Elements ads = doc.select("p.row");

def result = new StringBuilder();
int i = 0;

ads.forEach({ e ->
def id = e.attr("data-pid").toString()
def url = e.getElementsByTag("a").first().attr("href")

if (!old.contains(id)) {
old.add(id)
try {
i++;

if (i < 6) {
def link = baseUrl + url
Document doc2 = Jsoup.connect(link).get();
Elements details = doc2.select("section.body")

result.append("<a href=\"" + link + "\"><h2>Visit</h2></a>")
result.append(details.toString());
result.append("<br><br><br>");
}
} catch (Exception ex) {
ex.printStackTrace()
}
}
})

// Send e-mails
if (result.size() > 0 && !firstStart) {
def emails = config.getProperty("app.recipients").split(",");
emails.each {
simpleMail(config.getProperty("app.gmail.email"),
config.getProperty("app.gmail.password"),
it,
"${i} ads found",
result.toString()
);
}
}

// Append new adds to file
def writer = new PrintWriter(file)
old.each { id -> writer.println(id) }
writer.close()
}

This code is pretty simple. We have file old for accumulating ads which have been sent. After that we parse current results and check if we have it in list of sent ads. The implementation of simpleMail was grabbed from here without any changes - didn’t want to write it by myself. That’s it! Now we can start using it.

Running the app

First of all we have to build our app. It’s easy enough. We need to execute only one gradle task.

$ gradle uberjar

It produces craigslist-1.0.jar. Now we need to copy this file to folder where the app will be executed. Also you need to create app.properties with following content:

app.url=[craigslist search url (e.g. http://newyork.craigslist.org/search/mnh/nfa...)]
app.gmail.email=[gmail email which will be used as a sender]
app.gmail.password=[password for gmail account]
app.recipients=[email addresses of recipients separated by comma]

For statring the app I use small bashscript and start it by cron every 5 minutes.

cd /root/craigslist
java -jar /root/apts/craigslist-1.0.jar >> /root/craigslist/log

Conclusion

Developement with groovy is pretty fast and effective. I spended ~1 hour for full development and configuration. I didn’t get any troubles during development and building jar file and I got what I wanted.

All sources you can find in my github profile