java puzzlers from oca part 7

In this part of the Java Puzzlers from OCA series, I will show multiple ways of defining Strings and potential surprises related to that. Two basic types of creating Strings are creation with new keyword, and by just using the string literal.

String strWithNew = new String("hey");
String strWithLiteral = "ho";

As Strings are frequently used JVM uses a string pool and use the values in it so it won't have to create new objects for same values again and again. So seeing that the object address of same string literals are same should not be a surprise.

public class Puzzler {

    public static void main(String[] args) {

        String s1 = "myString";
        String s2 = "myString";

        System.out.println(s1 == s2); // true
    }
}

Ok then, this should be the same also right?

public class Puzzler {

    public static void main(String[] args) {


        String s1 = new String("myString");
        String s2 = new String("myString");

        System.out.println(s1 == s2);
    }
}

Not really. This will print "false". So if I create a new string with literal "myString" it is placed in the string pool. If I create it with new keyword then it's not searched in the pool, and when it's created it's also not placed in the string pool.

public class Puzzler {

    public static void main(String[] args) {


        String s1 = new String("myString");
        String s2 = new String("myString");
        String s3 = "myString";
        String s4 = "myString";

        System.out.println(s1 == s2);
        System.out.println(s2 == s3);
        System.out.println(s3 == s4);
        System.out.println(s1 == s4);
    }
}

I hope you can guess what happens above. s1 creates a new string and does not put it in the pool, s2 does the same thing. s3 takes a look to string pool does not see myString and creates it and places in the pool. s4 says "ah ok it is in the pool". So if we count how many strings are created, it is 3 and if we count what's placed in the pool it's 1 (myString). false, false, true, false are what's printed to the console.

java puzzlers from oca part 6

Even for new Java developers, constructors are probably no big mystery. In essence, when you create an instance of a class, the constructor of this class is started. In the 6th part of Java Puzzlers series, we will see a case related to constructors.

public class Puzzler {

    public Puzzler(){
        System.out.println("Puzzler no arg constructor");
    }

    public static void main(String[] args){
        Puzzler puzzler = new Puzzler();
    }
}

In the example above Puzzler() constructor will start and "Puzzler no arg constructor" will be printed to the screen. Now lets see a new example.

public class Puzzler {

    public void Puzzler(){
        System.out.println("Puzzler no arg constructor?");
    }

    public static void main(String[] args){
        Puzzler puzzler = new Puzzler();
    }
}

As you can see we added a return value to the constructor of Puzzler and you may expect that "Puzzler no arg constructor?" will get printed but this is not right. When we add a return value to the constuctor, it stops being a constructor. So it won't get started when a new instance is created.

java puzzlers from oca part 5

In the fifth part of the Java Puzzlers series, we will see something related to X.parseX(String s) methods.


You can see what we expect from X.parseX() methods.

public class Puzzler {

    public static void main(String[] args){
        int i = Integer.parseInt("2"); 
        System.out.println(i); // prints 2
    }
}

We give the methods a String that can be converted to the primitive representation and hope for the best. Now lets check another example which will give us a NumberFormatException.

public class Puzzler {

    public static void main(String[] args){
        int i = Integer.parseInt("integer"); // java.lang.NumberFormatException: For input string: "integer"
    }
}

As the input is a word and not something that can be parsed to an integer, we get NumberFormatException. What happens above is consistent for each number type. So Integer, Byte, Short, Long, Double, Float won't surprise you when you call their parse methods with some random String. You'll get a NumberFormatException.
Now lets check what happens with boolean.

public class Puzzler {

    public static void main(String[] args){
        final boolean b1 = Boolean.parseBoolean("boolean?");
        System.out.println(b1);
    }
}

Can you guess what happens? The parse call will probably throw java.lang.BooleanFormatException, right? Not really. If you run that, it'll print "false" to the screen. The reason is Boolean.parseBoolean() just accepts anything and if it can't parse it, it just returns "false" value. Now lets see the other example.

public class Puzzler {

    public static void main(String[] args){
        final boolean b2 = Boolean.parseBoolean("TrUe");
        System.out.println(b2);
    }
}

You probably expect false again? That's not the case because parseBoolean is case insensitive and will return "true" in this case.

java puzzlers from oca part 4

In the fourth part of Java Puzzlers, we have something related to char type.

public class Puzzler {

    public static void main(String[] args){
        char myChar = 'a';
        myChar++;

        System.out.println(myChar);
    }
}

You may have guessed it. It will print "b" and the reason for it is that char type is unsigned numeric primitive in the disguise of a character. So if I add one then I'll get the next character in unicode representation.

Then let's take a look at that one

public class Puzzler {

    public static void main(String[] args){
        char myChar = 'a';

        System.out.println(myChar + myChar);
    }
}

Will this print "aa"? Or  which's 97 + 97 = 194 (where 97 is value of 'a'). I don't know if you guessed it right but the result is neither. It's "194". When Java sees plus it tells "hmm that's an addition not a concat" and adds myChars up and returns the int value for it.

java puzzlers from oca part 3

In this third part of Java puzzlers, we will see a surprise in variable naming restrictions.


If I show you this, I'm sure you won't be surprised that this does not compile. static is one of the reserved keywords so why should it work?

public class Puzzler {

    public static void main(String[] args){

        int static = 2;
    }

}

Now I'll ask you a more difficult one. What you think about the below code. Will this compile?

public class Puzzler {

    public static void main(String[] args){
        int bool = 0;
        int integer = 1;
        int const = 2;
        int goto = 3;
    }
}

None of these should be reserved keyword. This is not C right? If you thought that it will compile, you're wrong. const and goto are reserved keywords, but bool and integer are fine.

java puzzlers from oca part 2

Welcome to the second part of Java Puzzlers from OCA. In this part we will see an interesting case about the underscore separator in numeric literals which came with Java 7.


In the below class you can see the separator underscore in the decimal literal. Also notice the class compiles now without a problem. Octal is the octal representation, binary is the binary and I'm sure you can't guess hex.

public class Puzzler {

    public static void main(String[] args){

        int decimal = 12_345;
        int octal = 04321;
        int binary = 0B1010;
        int hex = 0X4321A;
    }
} 

Octal literal is defined with 0, binary with 0b/0B and hex with 0x/0X. Ok then, let's begin putting _ for a better readability after them.

public class Puzzler {

    public static void main(String[] args){

        int decimal = 12_345;
        int octal = 0_4321;
        int binary = 0B1010;
        int hex = 0X4321A;
    }
} 

Neat. It compiles without a problem. Lets move to binary and hex.

public class Puzzler {

    public static void main(String[] args){

        int decimal = 12_345;
        int octal = 0_4321;
        int binary = 0B_1010;
        int hex = 0X_4321A;
    }
} 

Nope. You'll get "Illegal Underscore" there. I'm sure this is designed that way with something in mind, but it sure is a surprising behavior.

java puzzlers from oca part 1

I'm reading Oracle Certified Associate Java SE Programmer book from Mala Gupta in my spare time and I'm surprised with some of the new things I learn. Some of the time they really don't make sense, some of the time they make sense but really surprising to see. So in this article series, I wanted to share them as "Java Puzzlers" which sounded much cooler than "Java Surprises".


Lets check the below code and see what happens when we call an empty object reference's static method or field.

public class Puzzler {

    public static int field = 1;

    public static void printField() {
        System.out.println(field);
    }

    public static void main(String[] args){
        /*
        * Lets see what happens when the
        * reference is null.
        * */

        Puzzler puzzler = null;
        puzzler.printField(); // prints 1
        System.out.println(puzzler.field); // prints 1
    }

}

When you try to guess what will happen, you can think that we will get NullPointerException while doing the method and field calls as the reference does not have an object attached to it. But remember that static methods and fields belong to the class itself and not to the instance. So without the need of an associated object you can use them and won't get an exception for doing that. An also the way we call the static method are usually in Puzzler.printField() form which tells more.

lambdas and streams master class

If you want to master lambdas and streams from Java 8 & 9, you can check these java koans. That's one of the best koans I could find for a deeper learning. Also there are two videos on these koans: part1 and part2.

send your data async on kafka

For a project, I'm trying to log the basic transactions of the user such as addition and removal of an item and for multiple types of items and sending a message to kafka for each transaction. The accuracy of the log mechanism is not crucial and I don't want it to block my business code in the case of kafka server downtime. In this case an async approach for sending data to kafka is a better way to go.

My kafka producer code is in its boot project. For making it async, I just have to add two annotations: @EnableAsync and @Async.

@EnableAsync will be used in your configuration class (also remember that your class with @SpringBootApplication is also a config class) and will try to find a TaskExecutor bean. If not, it creates a SimpleAsyncTaskExecutor. SimpleAsyncTaskExecutor is ok for toy projects but for anything larger than that it's a bit risky since it does not limit concurrent threads and does not reuse threads. So to be safe, we will also add a task executor bean.

So,

@SpringBootApplication
public class KafkaUtilsApplication {
    public static void main(String[] args) {
        SpringApplication.run(KafkaUtilsApplication.class, args);
    }
}

will become

@EnableAsync
@SpringBootApplication
public class KafkaUtilsApplication {
    public static void main(String[] args) {
        SpringApplication.run(KafkaUtilsApplication.class, args);
    }

    @Bean
    public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(2);
        executor.setMaxPoolSize(2);
        executor.setQueueCapacity(500);
        executor.setThreadNamePrefix("KafkaMsgExecutor-");
        executor.initialize();
        return executor;
    }
}

As you can see there's not much change here. The default values I set should be tweaked based on your app's needs.

The second thing we need is addition of @Async.


My old code was:

@Service
public class KafkaProducerServiceImpl implements KafkaProducerService {

    private static final String TOPIC = "logs";

    @Autowired
    private KafkaTemplate<String, KafkaInfo> kafkaTemplate;

    @Override
    public void sendMessage(String id, KafkaType kafkaType, KafkaStatus kafkaStatus) {
        kafkaTemplate.send(TOPIC, new KafkaInfo(id, kafkaType, kafkaStatus);
    }
}

As you can see the sync code is quite straightforward. It just takes the kafkaTemplate and sends a message object to the "logs" topic. My new code is a bit longer than that.

@Service
public class KafkaProducerServiceImpl implements KafkaProducerService {

    private static final String TOPIC = "logs";

    @Autowired
    private KafkaTemplate kafkaTemplate;

    @Async
    @Override
    public void sendMessage(String id, KafkaType kafkaType, KafkaStatus kafkaStatus) {
        ListenableFuture<SendResult<String, KafkaInfo>> future = kafkaTemplate.send(TOPIC, new KafkaInfo(id, kafkaType, kafkaStatus));
        future.addCallback(new ListenableFutureCallback<>() {
            @Override
            public void onSuccess(final SendResult<String, KafkaInfo> message) {
                // left empty intentionally
            }

            @Override
            public void onFailure(final Throwable throwable) {
                // left empty intentionally

            }
        });
    }
}

Here onSuccess() is not really meaningful for me. But onFailure() I can log the exception so I'm informed if there's a problem with my kafka server.

There's another thing I have to share with you. For sending an object through kafkatemplate, I have to equip it with the serializer file I have.

public class KafkaInfoSerializer implements Serializer<kafkainfo> {

    @Override
    public void configure(Map map, boolean b) {
    }

    @Override
    public byte[] serialize(String arg0, KafkaInfo info) {
        byte[] retVal = null;
        ObjectMapper objectMapper = new ObjectMapper();
        try {
            retVal = objectMapper.writeValueAsString(info).getBytes();
        } catch (Exception e) {
            // log the exception
        }
        return retVal;
    }

    @Override
    public void close() {
    }
}

Also, don't forget to add the configuration for it. There are several ways of defining serializers for kafka. One of the easiest ways is adding it to application.properties. 

spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializer spring.kafka.producer.value-serializer=com.sezinkarli.kafkautils.serializer.KafkaInfoSerializer

Now you have a boot project that can send async objects to the desired topic.

spring annotations i never had the chance to use part 2: @ConfigurationProperties

Few days ago, I accidentally stumbled upon a Spring annotation from Spring Boot project while I was checking something else.

We all know how to bind property values with "@Value" to the classes and we all know that this can be quite cumbersome if there are multiple properties to bind. Spring Boot is here to help. You can use "@ConfigurationProperties" and bind multiple values quite concisely. We will give a prefix to differentiate other configs from ours. e.g. "@ConfigurationProperties(prefix = "jdbc")".
Any field this annotated class has is populated with property values from the property resource. For instance if it has a username parameter then property resource with "jdbc.username" key will populate this field. The most practical way of using this annotation is using it with "@Configuration".


You can check how we create the config class.

package com.sezinkarli.tryconfigprops;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;
import java.util.HashMap;
import java.util.Map;

@Configuration
@ConfigurationProperties(prefix = "jdbc")
public class JdbcConfig
{
    private String user;
    private String password;
    private String url;
    private String driver;

    public String getUser()
    {
        return user;
    }

    public void setUser(String user)
    {
        this.user = user;
    }

    public String getPassword()
    {
        return password;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public String getUrl()
    {
        return url;
    }

    public void setUrl(String url)
    {
        this.url = url;
    }

    public String getDriver()
    {
        return driver;
    }

    public void setDriver(String driver)
    {
        this.driver = driver;
    }

    public String getProperty(String key)
    {
        return propertyMap.get(key);
    }
}

And below you can check the properties we map from application properties

jdbc.user=myJdbcUser
jdbc.password=myPwd
jdbc.url=myUrl
jdbc.driver=myJdbcDriver

After that you can easily get these values by injecting the configuration class to somewhere.

@Service
public class YourService
{

    @Autowired
    private JdbcConfig jdbcConfig;
}

You can also check here for a working toy project using "@ConfigurationProperties".

benchmark for new string methods of java 11

While I was checking what's new in Java 11, I saw that there are several new methods for String class. So I wanted to do a microbenchmark with old way of doing things and by using new methods. These new methods are;

boolean isBlank()

String strip()

Stream lines()

isBlank() is tested agains trim().isEmpty(), strip() is tested agains trim() and lines() is tested agains split().

Here are the results:

Benchmark	Score
lines	3252919
split	2486539
strip	18280130
trim	18222362
isBlank	25126454
trim + isEmpty	19854156

Scores are based on operations per second so the more the better.
As you can see lines() is much faster than split().
strip() and trim() performed quite similar.
isBlank() outperformed trim() + empty().

You can check the benchmark code here.

custom deserialize your field in jackson

Currently I'm doing an integration to a third party service api. I had a trouble while trying to deserialize a field as a Date. Their json contains a date field with an odd formatting. e.g. /Date(1494579066000)/
So I have to deserialize it into a date by taking the number between paranthesis, then casting it to a Date object.
Here is my model for json

public class Result implements Serializable
{
    @JsonProperty("InspectionDate")
    @JsonDeserialize(using = MyCustomDeserializer.class, as = Date.class)
    private Date inspectionDate;
...
}

As you can see I tell Jackson to use my class for deserialization.
Now it is time to write the custom deserializer.
I'm extending JsonDeserializer and overriding deserialize method.
jsonParser will give me the field value and I'm going to parse millisecond part of the text then cast it to a Date object.

public class MyCustomDeserializer extends JsonDeserializer
{
    @Override
    public Date deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException
    {
        String timestampAsString = jsonParser.getText();

        if (StringUtils.isEmpty(timestampAsString))
        {
            return null;
        }

        Matcher matcher = Pattern.compile("/Date\\(([0-9]+)\\)/").matcher(timestampAsString);

        if (!matcher.find())
        {
            return null;
        }

        String millisecondAsString = matcher.group(1);

        if (StringUtils.isEmpty(millisecondAsString))
        {
            return null;
        }

        return new Date(Long.parseLong(millisecondAsString));
    }
}

I always thought that our use for Hibernate in projects is quite straightforward as a decision and very rarely we think if this is a good one or not. "How Hibernate Almost Ruined My Career" was quite a read and I recommend it to anyone who shouts "Hibernate" if there's some database-related stuff in the project in hand.

I was checking the actual Elasticsearch Java Api and while I created a NodeClient with the api I got lots of exceptions which is frustrating because I just did a clean install and there's nothing complicated in my pom.xml.
These are exceptions I got with the following of a huge stacktrace of course.

java.lang.ClassNotFoundException: groovy.lang.GroovyClassLoader
 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_66]

java.lang.ClassNotFoundException: com.github.mustachejava.Mustache
 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_66]
 

java.lang.ClassNotFoundException: org.apache.lucene.expressions.Expression
 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_66]
 

java.lang.ClassNotFoundException: com.sun.jna.Native
 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_66]

So I made maven generate a dependency tree, checked dependencies in elasticsearch client parent pom and added the necessary dependencies one by one by hand. Note that these are for Elasticsearch 2.1.1. For the version of your dependencies you should check org.elasticsearch.elasticsearch pom of your version of Elasticsearch.

  
 
            org.codehaus.groovy
            groovy-all
            2.4.4
        

        
            com.github.spullara.mustache.java
            compiler
            0.8.13
        

        
            org.apache.lucene
            lucene-expressions
            5.3.1
        

        
            net.java.dev.jna
            jna
            4.1.0
        

spring boot presentation for ozgur yazilim ve linux gunleri 2015

I did a Spring Boot Workshop at Ozgur Yazilim ve Linux Gunleri 2015 (Open-source Software and Linux Days for Turkish-free people). You can view the presentation below.

head first elastic search on java with spring boot and data features

In this article I'll try to give you an easy introduction on how to use Elastic Search in a Java project. As Spring Boot is the easiest and fastest way to begin our project I choose to use it. Futhermore, we will heavily use Repository goodies of beloved Spring Data.

Let's begin by installing Elastic Search on our machine and run our elastic server for the first time.

I go to elastic-folder\bin and run elasticsearch.bat (yeah I'm using Windows) but no luck. I get this:

"Error occurred during initialization of VM

Could not reserve enough space for object heap

Error: Could not create the Java Virtual Machine.

Error: A fatal exception has occurred. Program will exit."

What a great start!

In my bin folder there's a "elasticsearch.in.bat" file. I set ES_MAX_MEM=1g to 

ES_MAX_MEM=512mb and voila it is fixed.

I start a new server without problem after that.

Now it is time to define the document we will index in elastic search. Assume we have movie information to index. Our model is quite straightforward. Movie has a name, rating and a genre in it. I chose "elastic_sample" as index name which sounds good as a database name and "movie" as type which is good for a table name if we think in relational database terms. Nothing fancy in the model as you can see.

@Document(indexName = "elastic_sample", type = "movie")
public class Movie {

    @Id
    private String id;

    private String name;

    @Field(type = FieldType.Nested)
    private List &lt Genre &gt  genre;

    private Double rating;

    public Double getRating() {
        return rating;
    }

    public void setRating(Double rating) {
        this.rating = rating;
    }

    public void setId(String id) {
        this.id = id;
    }

    public List &lt Genre &gt  getGenre() {
        return genre;
    }

    public void setGenre(List &lt Genre &gt  genre) {
        this.genre = genre;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;

    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Movie{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", genre=" + genre +
                ", rating=" + rating +
                '}';
    }
}

For those who wonder what Genre is here is it. Just a POJO.

public class Genre {
    private String name;

    public Genre() {
    }

    public Genre(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Genre{" +
                "name='" + name + '\'' +
                '}';
    }

    public void setName(String name) {
        this.name = name;
    }
}

Not it is time to create DAO layer so we can save and load our document to/from our elastic search server. Our Repository extends the classic ElasticserchRepository (no idea why it is search and not Search). As you probably know Spring Data can query one or more fields with these predefined methods where we use our field names. findByName will search in the name field, findByRating will search in the rating field so on so forth. Furthermore thanks to Spring Data we don't need to write implementation for it, we just put method names in the interface and that's finished.

public interface MovieRepository extends ElasticsearchRepository &lt Movie, Long &gt {
    public List &lt Movie &gt  findByName(String name);

    public List &lt Movie&gt  findByRatingBetween(Double beginning, Double end);
}

Our DAO layer will be called by a Service layer:

@Service
public class MovieService {

    @Autowired
    private MovieRepository repository;

    public List &lt Movie &gt  getByName(String name) {
        return repository.findByName(name);
    }

    public List &lt Movie &gt  getByRatingInterval(Double beginning, Double end) {
        return repository.findByRatingBetween(beginning, end);
    }

    public void addMovie(Movie movie) {
        repository.save(movie);
    }
}

Here is the main Class we will use to run our application. EnableAutoConfiguration will auto-configure everything it recognizes under our classpath. ComponentScan will scan for Spring annotations under the main Class' directory.

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class BootElastic implements CommandLineRunner {

    @Autowired
    private MovieService movieService;

    private static final Logger logger = LoggerFactory.getLogger(BootElastic.class);

// add star wars and
// princess bride as a movie
// to elastic search
    private void addSomeMovies() {
        Movie starWars = getFirstMovie();
        movieService.addMovie(starWars);

        Movie princessBride = getSecondMovie();
        movieService.addMovie(princessBride);
    }

    private Movie getSecondMovie() {
        Movie secondMovie = new Movie();
        secondMovie.setId("2");
        secondMovie.setRating(8.4d);
        secondMovie.setName("The Princess Bride");

        List &lt Genre &gt  princessPrideGenre = new ArrayList &lt Genre &gt();
        princessPrideGenre.add(new Genre("ACTION"));
        princessPrideGenre.add(new Genre("ROMANCE"));
        secondMovie.setGenre(princessPrideGenre);

        return secondMovie;
    }


    private Movie getFirstMovie() {
        Movie firstMovie = new Movie();
        firstMovie.setId("1");
        firstMovie.setRating(9.6d);
        firstMovie.setName("Star Wars");

        List &lt Genre &gt  starWarsGenre = new ArrayList &lt Genre &gt();
        starWarsGenre.add(new Genre("ACTION"));
        starWarsGenre.add(new Genre("SCI_FI"));
        firstMovie.setGenre(starWarsGenre);

        return firstMovie;
    }

    public void run(String... args) throws Exception {
        addSomeMovies();
        // We indexed star wars and pricess bride to our movie
        // listing in elastic search

        //Lets query if we have a movie with Star Wars as name
        List &lt Movie &gt starWarsNameQuery = movieService.getByName("Star Wars");
        logger.info("Content of star wars name query is {}", starWarsNameQuery);

        //Lets query if we have a movie with The Princess Bride as name
        List &lt Movie &gt  brideQuery = movieService.getByName("The Princess Bride");
        logger.info("Content of princess bride name query is {}", brideQuery);


        //Lets query if we have a movie with rating between 6 and 9
        List &lt Movie &gt  byRatingInterval = movieService.getByRatingInterval(6d, 9d);
        logger.info("Content of Rating Interval query is {}", byRatingInterval);
    }

    public static void main(String[] args) throws Exception {
        SpringApplication.run(BootElastic.class, args);
    }
}

If we run it the result is:

015-02-28 18:26:12.368  INFO 3616 --- [           main] main.BootElastic: Content of star wars name query is [Movie{id=1, name='Star Wars', genre=[Genre{name='ACTION'}, Genre{name='SCI_FI'}], rating=9.6}]
2015-02-28 18:26:12.373  INFO 3616 --- [           main] main.BootElastic: Content of princess bride name query is [Movie{id=2, name='The Princess Bride', genre=[Genre{name='ACTION'}, Genre{name='ROMANCE'}], rating=8.4}]
2015-02-28 18:26:12.384  INFO 3616 --- [           main] main.BootElastic: Content of Rating Interval query is [Movie{id=2, name='The Princess Bride', genre=[Genre{name='ACTION'}, Genre{name='ROMANCE'}], rating=8.4}]

As you can see the interval query only retrieved Princess Bride. We did not do any configuration right? It is unusual. I have to share the huge configuration file with you:

spring.data.elasticsearch.cluster-nodes=localhost:9300
 # if spring data repository support is enabled
spring.data.elasticsearch.repositories.enabled=true

Normally you would use port 9200 when you query your elastic server. But when we programmatically reach it we are using 9300. If you have more than one node you would separate them with a comma and use 9301, 9302 etc as port numbers. Our pom file is no surprise either. Just elastic starter pom and we are set to go.

    4.0.0

    caught.co.nr
    boot-elastic-sample
    1.0-SNAPSHOT
    war

    
    
        org.springframework.boot
        spring-boot-starter-parent
        1.2.2.RELEASE
    

    
        
            org.springframework.boot
            spring-boot-starter-data-elasticsearch
        

    

    
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

As you can see thanks to Spring Boot and Data it is quite easy to work with elastic search. Lets check what we indexed from the server api as well. I'll use Sense -a chrome plug-in for elastic commands-.

Here's the result json:

{
   "took": 2,
   "timed_out": false,
   "_shards": {
      "total": 1,
      "successful": 1,
      "failed": 0
   },
   "hits": {
      "total": 2,
      "max_score": 1,
      "hits": [
         {
            "_index": "elastic_sample",
            "_type": "movie",
            "_id": "1",
            "_score": 1,
            "_source": {
               "id": 1,
               "name": "Star Wars",
               "genre": [
                  {
                     "name": "ACTION"
                  },
                  {
                     "name": "SCI_FI"
                  }
               ]
            }
         },
         {
            "_index": "elastic_sample",
            "_type": "movie",
            "_id": "2",
            "_score": 1,
            "_source": {
               "id": 2,
               "name": "The Princess Bride",
               "genre": [
                  {
                     "name": "ACTION"
                  },
                  {
                     "name": "ROMANCE"
                  }
               ]
            }
         }
      ]
   }
}

You can check out the whole project in the github.

err: non-serializable object

I'm using Cacheable annotation and getting "err: Non-serializable object" from the underlying caching mechanism (memcache). My code was such as this:

public class MyResult implements Serializable
{
private MyEnum myEnum;
private AnotherObject anotherObj;
}

It is implementing Serializable why it would not work? That's because I forgot that every object in my class must also implement Serializable. So adding this to AnotherObject fixed my problem. But I did not implement Serializable in MyEnum, why it worked? It worked because enums in Java by default implement Serializable.

spring social example on spring boot or how I stopped worrying and loved autoconfiguration

As of Spring Boot 1.1.0.RC1, autoconfiguration and the starter pom of Spring Social  is added which means that I won't have to add a hundred dependency to my pom and lots of meaningless Spring configuration will be handled for me. Let's see how it works on an example.

 I will implement a web application of two pages. One will show the given user's Twitter timeline and the other user's profile information. Here's my pom:

    4.0.0

    nr.co.caught
    BootTwitterJoy
    1.0-SNAPSHOT
    war

    
    
        org.springframework.boot
        spring-boot-starter-parent
        1.1.0.RC1
    

    
        
            org.springframework.boot
            spring-boot-starter-social-twitter
        

        
        
            org.apache.tomcat.embed
            tomcat-embed-jasper
        
        
            javax.servlet
            jstl
        

    

    
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

    
    
    
        
            spring-snapshots
            http://repo.spring.io/snapshot
            
                true
            
        
        
            spring-milestones
            http://repo.spring.io/milestone
        
    
    
        
            spring-snapshots
            http://repo.spring.io/snapshot
        
        
            spring-milestones
            http://repo.spring.io/milestone
        
    

As you can see, I have my starter-social-twitter dependency which gives me Spring Social and Web capabilities. I'll add jasper and jstl for my jsp pages to work. My repositories part is quite populated due to the milestone repositories.
Now we will add our Service to do Twitter method calls and a Controller for handling the requests. Our Controller is plain and simple:

@Controller
public class TwitterController {

    @Autowired
    private TwitterService twitterService;

 @RequestMapping(value = "/timeline/{twitterUser}")
 public String getUserTimeline(@PathVariable String twitterUser, Model model) {
        model.addAttribute("tweets", twitterService.getUserTimeline(twitterUser));
        model.addAttribute("user", twitterUser);

  return "timeline";
 }

    @RequestMapping(value = "/profile/{twitterUser}")
    public String getUserProfile(@PathVariable String twitterUser, Model model) {
        model.addAttribute("userProfile", twitterService.getUserProfile(twitterUser));

        return "profile";
    }
}

If the request comes with "/timeline/username", our controller will get the user timeline and if it comes with "/profile/username" it will get the user profile from TwitterService. Here's our TwitterService:

@Service
public class TwitterService {

   @Autowired
    private Twitter twitter;

    public List < Tweet > getUserTimeline(String twitterUser) {
        TimelineOperations timelineOps = twitter.timelineOperations();
        List tweets = timelineOps.getUserTimeline("@" + twitterUser);

        return tweets;
    }

    public TwitterProfile getUserProfile(String twitterUser) {
        UserOperations userOperations = twitter.userOperations();
        TwitterProfile userProfile = userOperations.getUserProfile(twitterUser);

        return userProfile;
    }
}

We have a Twitter object that'll be created thanks to Spring Boot's autoconfiguration. We just have to provide an app id and app secret key (a.k.a. consumer key and consumer secret) in our application properties and Boot will do the rest. I'm quoting Twitter object explanation from Spring javadoc: "This instance of TwitterTemplate is limited to only performing operations requiring client authorization. For instance, you can use it to search Twitter, but you cannot use it to post a status update. The client credentials given here are used to obtain a client access token via OAuth 2 Client Credentials Grant". If you try to do a status update, you'll get "org.springframework.social.MissingAuthorizationException: Authorization is required for the operation, but the API binding was created without authorization". For further Twitter functionality, we would need to provide access token and access token secret keys as well but as far as I know autoconfiguration would not handle these cases yet.
My JSPs:
profile.jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title></title>
</head>
<body>
<img src="${userProfile.profileImageUrl}"/>  

Screen name: ${userProfile.screenName} 

Name: ${userProfile.name}      

Description: ${userProfile.description}   

Location:  ${userProfile.location}  

Followers: ${userProfile.followersCount}  

</body>
</html>

As you can see, profile takes the userProfile provided by our Controller and show the basic profile properties. timeline.jsp

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Time Line for <c:out value="${twitterUser}" /> TimeLine</title>
</head>
<body>
<ul>
    <c:forEach items="${tweets}" var="tweet">
        <li>${tweet.text}
 at <c:out value="${tweet.createdAt}"/></li>
        <br/>
    </c:forEach>
</ul>
</body>
</html>

Tweets are shown with their text and creation date. My application.properties content:

# Config for JSPs
spring.view.prefix: /WEB-INF/jsp/
spring.view.suffix: .jsp

# SPRING SOCIAL TWITTER (TwitterAutoConfiguration)
spring.social.twitter.appId= someAppId
spring.social.twitter.appSecret= someSecretId

spring.view properties are for the jsp handling. spring.social.twitter properties can be obtained from http://dev.twitter.com. Just login there with your twitter account, create your app and get your api keys. Here's the result:

You can check the code at github.

how to build your web application on spring boot and deploy it on heroku

Why would you need a tutorial for building your web application on spring boot and deploying it on heroku?
That's because our web application will serve JSP files and as Spring Boot's JSP support is limited we will have to use war files for deployment and it can get a bit tricky to deploy it on heroku. Furthermore, as the web application we will deploy is super concise you can use it on your own project by just editing it.

Our controller is quite basic. It will take the name of the user from url and print it on the next page. So calling "/hello/sezin" will print on "hello sezin" on the page.

package main.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;

/**
 * @author sezin karli (skarligmail.com)
 * @since 3/19/14 3:42 PM
 *        User: Sezin Karli
 */
@Controller
@RequestMapping(value = "/hello")
public class HelloController {

    @RequestMapping(value = "/{user}")
    public String handleOne(@PathVariable String user, ModelMap modelMap){
        String helloToken = "Hello " + user;
        modelMap.put("token", helloToken);
        return "welcome-page";
    }
}

Our main Spring class is below. PORT attribute is taken from environment variables if it can't be found 8080 is used. This part is a requirement for Heroku.

package main;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @author sezin karli (skarligmail.com)
 * @since 3/19/14 9:26 AM
 *        User: Sezin Karli
 */
@Configuration
@EnableAutoConfiguration
@ComponentScan
public class ToyProjectLauncher {

    public static void main(String[] args) throws Exception {
        String webPort = System.getenv("PORT");
        if (webPort == null || webPort.isEmpty()) {
            webPort = "8080";
        }
        System.setProperty("server.port", webPort);

        SpringApplication.run(ToyProjectLauncher.class, args);
    }
}

Our application properties. We need to show a folder for jsp files and if we don't want to print ".jsp" suffix for every return value in the controller we will also need the suffix parameter below.

server.port: ${port:8080}
spring.view.prefix: /WEB-INF/jsp/
spring.view.suffix: .jsp

Our jsp is as follows. We just print the token we get from the controller.

<%@ page language="java" contentType="text/html; charset=US-ASCII"
         pageEncoding="US-ASCII"%>



    
    
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
    

If we analyze the pom below you can see that we have a spring boot parent which's needed to inherit defaults from spring boot. Then we add starter-web dependency because it will add web dependency template. Jasper and jstl dependencies are needed for JSPs to work. We would need spring-boot-maven-plugin if we want a fat jar which makes it easier to deploy.

    4.0.0

    nr.co.caught
    boot-toy-project
    1.0-SNAPSHOT
    war


    
    
        org.springframework.boot
        spring-boot-starter-parent
        1.0.0.BUILD-SNAPSHOT
    

    
        
            org.springframework.boot
            spring-boot-starter-web
        

        
        
            org.apache.tomcat.embed
            tomcat-embed-jasper
        
        
            javax.servlet
            jstl
        

    

    
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

    
        
            spring-snapshots
            Spring Snapshots
            http://repo.spring.io/snapshot
            
                true
            
        
    

    
        
            spring-snapshots
            http://repo.spring.io/snapshot
        
    

You can check GitHub if you need further details with the project. If everyting's fine you should be able to build it with "mvn package".
You must see your war file under target folder. Why a war file? Because Spring Boot supports JSPs only if the project package is war.
 Lets run our code by going under "target" and doing "java -jar boot-toy-project-1.0-SNAPSHOT.war". You should see your hello page if you type "localhost/hello/sezin".

Now we will continue by deploying it on heroku. I assume you already have a heroku user and heroku toolbelt already installed.

Open a command prompt and login to heroku by typing "heroku login". Type your heroku email and password. It says "could not find an existing public key. We try to generate one but get a "could not generate key: 'ssh-keygen' is not recognized" error (under windows 7).

There seems to be a problem.
Open a git bash and lets create an ssh key with 'ssh-keygen -t rsa -C "yourEmail"' command.

Lets login again and here we get "authentication successful".

After that we will try to push and deploy our Spring Boot Project.
Create a file named "Procfile" with the information below under our project folder

 web: java $JAVA_OPTS -jar target/boot-toy-project-1.0-SNAPSHOT.war

There's another way to deploy war files to heroku (heroku deploy:war), but I didn't manage to run my application with it so I'm teaching you what worked for me. :)

Now, create a project with "heroku create" command. We will get "Git remote heroku added".

Open git bash and enter "git push heroku master" under your project directory. Now we will push our code into heroku git and heroku will deploy it to our server.

The last line will show you on which address your site is available. Mine was "http://pure-shelf-8719.herokuapp.com/". I add few strings to test my hello page and go to "http://pure-shelf-8719.herokuapp.com/hello/world". You can see the awesome result below.

expression language injection attacks with the help of springJspExpressionSupport

Recently, I discovered a nasty place for expression language injection attack in one of my applications. This was directly related to the expression evaluation feature of spring components on jsp.
I was adding a request parameter to a spring form's action and as spring's form component directly evaluates it, you were able to put a ${applicationScope} (or anything on the page) on the request parameter and see the evaluation result on the source code.

First thing to do was setting springJspExpressionSupport to false by editing my web.xml and setting the flag to false.

 
        Enable Spring JSP Expressions
        springJspExpressionSupport
        false
    

The problem with this is the fact that it totally disables Spring's evaluation mechanism which means  ExpressionEvaluationUtils.evaluate() calls won't work anymore. So I had to use an alternative way such as the following code:

ELContext elContext = pageContext.getELContext();
JspApplicationContext jac = JspFactory.getDefaultFactory().getJspApplicationContext(pageContext.getServletContext());
 ValueExpression val = jac.getExpressionFactory().createValueExpression(elContext, exp, resultClass);

return val.getValue(elContext);