#dropwizard

Backend Java Developer | San Francisco, CA, USA

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Summary: As a senior member of our Agile team, you understand how to leverage Java to rapidly build RESTful APIs that are easy to understand, use and maintain. You know how to deal with external and internal clients to your services, and know how to make the…

Even some popular libraries make upgrade to recent versions such a difficult task that if there are not major security fixes most people drag the older versions along with the product till such a time that incompatibilities with other projects emerge or use of new features necessitates such a move.

We upgraded one of the core libraries of one of our projects recently - Dropwizard - from 0.6 to 0.9 and as luck would have it, 0.6 to 0.7 a whole world changed for Dropwizard!

Here’s a guide that provided a lot of valuable information that I see no reason to reproduce: https://intentmedia.com/upgrading-dropwizard-0-6-to-0-7/

Here are a few other things that were not covered or well defined in the guide that, along with the guide, should be sufficient to help you upgrade to a more recent version of Dropwizard -

Server configuration:

If you have been using the same port for application and admin endpoints in the previous versions, with the upgrade you would get a Bind exception. In the earlier version if the same port is given Dropwizard would automatically use the same for admin endpoints and expose them at /admin. The documentation around this is not very clear but in such a case you would need to use the "simple" server type which would take just a single port.

Views:

Some of you may have heard of the TechEmpower Web Framework Benchmarks. As it turns out, the open source project that I’m involved with (Dropwizard) is featured in the benchmark. Dropwizard hasn’t fared terribly well in the benchmark, however, which is surprising because I’ve seen it in production. It’s been pretty snappy.

Determined to get to the bottom of the results (maybe I should rephrase that), I’ve forked and locally cloned the benchmark repo, located Dropwizard in the frameworks/Java/dropwizard directory, and followed the README.md instructions to run the benchmark locally.

The results aren’t pretty. Granted, the benchmark runs inside a VirtualBox instance alongside the Dropwizard app and a MySQL database. It’s not the raw latency that concerns me so much as the standard deviation and the long tail latency (i.e. latency at the 99th percentile). These are typically indications of scaling issues. Even at 8 concurrent connections with 2 driving threads, long tail latency for a simple JSON endpoint is alarmingly high:

Running 15s test @ http://127.0.0.1:9090/json 2 threads and 8 connections Thread Stats Avg Stdev Max +/- Stdev Latency 1.08ms 2.36ms 55.03ms 95.36% Req/Sec 5.81k 626.98 7.28k 82.67% Latency Distribution 50% 602.00us 75% 732.00us 90% 1.20ms 99% 12.42ms 173528 requests in 15.01s, 27.47MB read Requests/sec: 11561.92

As you can see, 75% of requests finish in under 1 millisecond. Even at 90% we’re still finishing in just over 1 millisecond. The slowest 1% of requests, however, take more than 10 milliseconds. As the concurrency maxes out at 256 connections and 2 threads, the median response time is unnacceptably slow for such a basic endpoint (even for an underpowered virtual machine) and the 99th percentile is heading towards 1 second:

Running 15s test @ http://127.0.0.1:9090/json 2 threads and 256 connections Thread Stats Avg Stdev Max +/- Stdev Latency 74.24ms 130.63ms 1.28s 88.12% Req/Sec 5.45k 0.94k 8.24k 72.00% Latency Distribution 50% 15.04ms 75% 85.84ms 90% 233.41ms 99% 620.43ms 162873 requests in 15.01s, 25.78MB read Requests/sec: 10848.85

Equipped with the fabulous IntelliJ IDEA, the indispensable Java Mission Control, insatiable curiosity, and a desire to see Dropwizard move up the ranks a bit I’m going to dive into the benchmark, into Dropwizard, and into Dropwizard’s dependencies to see what I can learn and what I can improve. I plan to do a series of posts showing my methods and remedies in the hope that it proves useful or educational to others.

My application is depeloped using a simple frameworl Dropwizard. Here a mini tutorial: https://blog.openshift.com/day-13-dropwizard-the-awesome-java-rest-server-stack/

Now I've to deploy application on OpenShift. Here some tips during deployment.

1° PROBLEM

By default ‘diy’ cartridge uses java 7. I’ve to use java 8 in my application so I’ve found this hit for installing java 8 on my application: 

http://stackoverflow.com/questions/23894323/jdk-8-support-at-diy-cartridge-in-openshift

It’s works well.

Now following these instructions: http://dmly.github.io/blog/2013/05/01/diy-java-app-server-on-openshift-so-far-so-good/

But,

2° PROBLEM

Running maven, It can’t write in defaul repository for missing permission, so I’ve found a solution by specifing in sessings.xml file the repisitory location in my $OPENSHIFT_DATA_DIR

Here the explanation, how to run maven locally: 

https://forums.openshift.com/maven-could-not-create-local-repository

But,

3° PROBLEM

Even when I specify JAVA_HOME to my java 8 installation, the default maven, yet installed by default on Openshift, uses java 7, so It gives problems compiling source, executing maven task:

+ mvn package -s /var/lib/openshift/566e8b000c1e66efec00002f/app-root/runtime/repo//.openshift/settings.xml -q clean package [debug] execute contextualize [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.3:compile (default-compile) on project classcard_gest: Fatal error compiling: invalid target release: 1.8 -> [Help 1] [ERROR] [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. [ERROR] [ERROR] For more information about the errors and possible solutions, please read the following articles: [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

In fact from command line on connecting to my gear:

[classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> export JAVA_HOME="${OPENSHIFT_DATA_DIR}jdk1.8.0_05" [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> export PATH=${OPENSHIFT_DATA_DIR}jdk1.8.0_05/bin:$PATH [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> java -version java version "1.8.0_05" Java(TM) SE Runtime Environment (build 1.8.0_05-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode) [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> javac -version javac 1.8.0_05 [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\> mvn -version Apache Maven 3.0.4 (r1232336; 2012-12-18 14:36:37-0500) Maven home: /usr/share/java/apache-maven-3.0.4 Java version: 1.7.0_91, vendor: Oracle Corporation Java home: /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.91/jre Default locale: en_US, platform encoding: UTF-8 OS name: "linux", version: "2.6.32-504.34.1.el6.x86_64", arch: "i386", family: "unix" [classcardapp-simplethings.rhcloud.com 566e8b000c1e66efec00002f]\>

Here some explanation:

http://stackoverflow.com/questions/33460703/openshift-maven-project-fails-to-find-java-8-compiler

https://bugzilla.redhat.com/show_bug.cgi?id=1109980

https://developer.jboss.org/people/fjuma/blog/2014/06/03/wildfly-810final-on-openshift--with-jdk-8-support

So I’ve to installa a mvn in my $OPENSHIFT_DATA_DIR and uses this one.

An example hook for installing maven

Example on using java enums in Jersey for converting string values in emums and from enums to sting value.

Example class: DurationUnitParam Note @JsonValue in DurationUnit for controllong the enum representation.

Resources:

What Makes Jersey Interesting: Parameter Classes - http://codahale.com/what-makes-jersey-interesting-parameter-classes/

Jackson – Serialize Enums as JSON Objects - http://www.baeldung.com/jackson-serialize-enums

package it.classcard.classcard_gest.params; import javax.ws.rs.WebApplicationException; import javax.ws.rs.core.Response; import javax.ws.rs.core.Response.Status; import com.fasterxml.jackson.annotation.JsonValue; public class DurationUnitParam { public static enum DurationUnit { DAY("D"), MONTH("M"), YEAR("Y"); private String name; DurationUnit(String name){ this.name = name; } @JsonValue public final String getName(){ return name; } } private DurationUnit durationUnit; /** * Permitted values are: D for days, M for month and Y for years. * * @param durationUnitValue */ public DurationUnitParam(String durationUnitValue) throws WebApplicationException { if("D".equals(durationUnitValue)){ durationUnit = DurationUnit.DAY; } else if("M".equals(durationUnitValue)){ durationUnit = DurationUnit.MONTH; } else if("Y".equals(durationUnitValue)){ durationUnit = DurationUnit.YEAR; } else { throw new WebApplicationException( Response .status(Status.BAD_REQUEST) .entity("Couldn't parse unit: " + durationUnitValue ) .build() ); } } public DurationUnit getDurationUnit(){ return durationUnit; } }

Slide deck and accompanying write up following a recent lightning talk I did at my workplace on using Heroku for HA dropwizard apps.

Say you want to use JDBI's SQL Object API and have an insert statement that you want to run, for example:

INSERT INTO users (first_name, age) VALUES (:firstName, :age);

but your User class looks like:

class User { String firstName; String Date dateOfBirth; // constructor(s) // getters public int getAge() { // ... some vodoo to calculate age... } }

Writing a JDBI UserDao with the following method would crash since there is no "age" field in the User class and JDBI doesn't know how to bind to the ":age" parameter.

public void saveUser(@BindBean User user);

Start by creating a custom binding:

@BindingAnnotation(BindUser.UserBinderFactory.class) @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.PARAMETER}) public @interface BindUser { public static class UserBinderFactory implements BinderFactory { public Binder build(Annotation annotation) { return new Binder<BindUser, User>() { public void bind(SQLStatement q, BindUser bind, User user) { q.bind("firstName", user.getFirstName()); q.bind("age", user.getAge()); } }; } } }

Then change your saveUser() method to use the binding you just created:

public void saveUser(@BindUser User user);