Tag: spring boot

Posted on

Building a Spring Boot RestController to search Redis

I’ve just started taking a look at using Redis. I wondered what it would look like to build a simple REST interface with Spring Boot. Spring Data Redis makes this pretty simple.

First up, you need to configure a @Bean in your @SpringBootApplication class (full source is on github here):

@Bean
RedisTemplate<String, Object> redisTemplate() {
  RedisTemplate<String, Object> template = new RedisTemplate<String, Object>();
  template.setConnectionFactory(jedisConnectionFactory());

  // these are required to ensure keys and values are correctly serialized
  template.setKeySerializer(new StringRedisSerializer());
  template.setHashValueSerializer(new GenericToStringSerializer<Object>(Object.class));
  template.setValueSerializer(new GenericToStringSerializer<Object>(Object.class));
  return template;
}

This is connecting with default settings to a locally running Redis.

Wire up a RedisTemplate into a Controller like this:

@RestController
public class RedisRestController {

  @Autowired
  private RedisTemplate<String, Object> template;

  @GetMapping("singlekey/{key}")
  public RedisResult getSingleValue(@PathVariable("key") String key){
    String value = (String)this.template.opsForValue().get(key);
    RedisResult result = new RedisResult(key, value);
    return result;
  }
}

and this is a bare minimum to get started, but shows how easy it is to get stuff up and running with Spring Boot and other projects like Spring Data.

Send a GET to /singlekey/ with a key value and json for the result is returned.

Posted on

Spring Boot RestController Error: “No converter found for return value of type”

Spring Boot RestControllers by default can return a Pojo class as the return result from a mapped request method, and it is converted into a Json result. I’ve run into this issue before though, and it’s not immediately obvious what’s wrong: ‘No converter found for return value of type’ :

java.lang.IllegalArgumentException: No converter found for return value 
of type: class kh.springboot.redis.domain.RedisResult
at org.springframework.web.servlet.mvc.method.annotation
.AbstractMessageConverterMethodProcessor
.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:187) ~[spring-webmvc-4.3.6.RELEASE.jar:4.3.6.RELEASE]

My returned class from my @GetMapping method is just a simple Pojo:

public class RedisResult {

private String key;
private String value;

public RedisResult(String key, String value) {
  this.key = key;
  this.value = value;
  }
}

And my @RestController is a simple controller with a single @GetMapping (in this case I’m building a REST endpoint to query key values from Redis using Spring Data Redis RedisTemplate:

@RestController

public class RedisRestController {

  @Autowired
  @Qualifier("RedisTemplate")
  private RedisTemplate template;

  @GetMapping("singlekey/{key}")
  public RedisResult getSingleValue(@PathVariable("key") String key){
    String value = (String)this.template.opsForValue().get(key);
    RedisResult result = new RedisResult(key, value);
    return result;
  }
}

If you’ve found my post because you have this same issue, before you go down the rabbit hole adding additional Maven dependencies or additional annotations you think might be missing, the reason is usually that your Pojo class you are returning doesn’t have any public getter methods. For each property in your Pojo you want returned in your Json, make sure you have a public getter.

This is discussed in this StackOverflow post here.

Posted on

Spring Boot: cannot find classfile ConfigurableApplicationContext (invalid LOC header)

Spring Boot with it’s maven starter dependencies is incredibly helpful to get a simple Spring Boot app up and running in no time, but occasionally you run into weird errors in Eclipse like:

The project was not built since its build path is incomplete. 
Cannot find the class file for 
org.springframework.context.ConfigurableApplicationContext. 
Fix the build path then try building this project

Or doing a mvn compile from your shell, something like:

[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] error reading /Users/kev/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/8.5.11/tomcat-embed-core-8.5.11.jar; invalid LOC header (bad signature)

Assuming you’re already using the Spring Boot Starter Web dependency:

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>

.. errors about Classes not found or errors reading .jars (‘invalid LOC header’) could be related to jars in your local .m2 repo being corrupt.

This is pretty easy to correct if you go into your ~/.m2/repository/ and delete your downloaded dependencies. You can be more specific in what you delete if you have something that you can easily identify as coming from a specific dependency.

Posted on

Building a multi-container Spring Boot and MongoDB webapp with Docker 1.12.x – part 2

In the first part of this article, I showed how I split the frontend, backend and database all into their own containers, and how each could be individually scaled using docker-compose.

If you’re already familiar with docker-compose and using haproxy for load balancing against container, you might have noticed there’s a limitation in my approach, as both the backend REST service was exposing it’s port 8080 externally, and so I don’t think HTTP requests from the frontend browser in the app were ever passing through the haproxy to be load balanced, only the requests to load the front end on port 80 were being load balanced.

I looked into how I could configure haproxy with multiple backends, listening on different ports, but eventually came to the conclusion that adding two different haproxy containers, one load balancing for port 80 and one for port 8080 was easy to do.

I’m not sure if this is the best way to approach this, but it certainly. works. Leave me a comment if you have any suggestions.

Here’s my final docker-compose.yml:

 

version: '2'
  
services:
    mongodata:
        image: mongo:3.2
        volumes:
        - /data/db
        entrypoint: /bin/bash
    mongo:
        image: mongo:3.2
        depends_on: 
            - mongodata
        volumes_from:
            - mongodata
        ports:
            - "27017"
    addressbook:
        image: addressbook
        depends_on: 
            - mongo
        environment:
            - MONGODB_DB_NAME=addressbook
        ports:
            - "8080"
        links:
            - mongo
    web:
        image: docker-web-angularjs
        ports:
            - "80"
    lb-web:
        image: dockercloud/haproxy
        depends_on: 
            - web
        environment:
            - STATS_PORT=1936
            - STATS_AUTH="admin:your-password"
        links:
            - web
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock
        ports:
            - 80:80
            - 1936:1936
    lb-addressbook:
        image: dockercloud/haproxy
        depends_on: 
            - addressbook
        environment:
            - STATS_PORT=1937
            - STATS_AUTH="admin:your-password"
        links:
            - addressbook
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock
        ports:
            - 8080:80
            - 1937:1937
Proudly powered by WordPress