Tech Notes – Page 22 – Kev's Development Toolbox

February 13, 2017

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.

February 11, 2017

Redis: getting started and basics

Redis is a key/value in-memory datastore. The Getting Started guide will get you up and running pretty quick.

Startup:

./redis-server

CLI:

./redis-cli

From cli, inserting a value:

set key value

Get a value:

get key

List keys:

keys pattern

List all keys, not recommended against a large prod database:

keys *

January 19, 2017

Unit testing React components with Jest

Jest is a unit test framework for testing React apps. The Getting Started guide is pretty much all you need to get started. If you’ve created your project using create-react-app then you’re already setup, just run ‘npm test’ and a runner will test up that repeatedly runs your tests as you make code or test changes.

create-react-app also creates a sample test for the sample App.js component. This is a good starting point to follow for other tests:

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';

it('renders without crashing', () => {
  const div = document.createElement('div');
  ReactDOM.render(<App/>, div);
});

To test the results of rendering a component, the enzyme library allows you to easily capture the output from a render, and then query the results. For example:

import React from 'react';
import ReactDOM from 'react-dom';
import {shallow, mount} from 'enzyme';
import Calculator from '../Components/CalculatorComponent';
it('renders with result 3', () => {
    const result = mount(<Calculator value1="1" value2="2" />);
    result.find('button').simulate('click');
    const buttonResult = result.find("#result").first();
    expect(buttonResult.text()).toEqual("3");
});

The CalculatorComponent I’m testing here is the one from my previous React post.

December 26, 2016

React ES5 to ES6: props and state

Developing with React and ES5, state on a Component is configured using the getInitialState() function:

var ButtonComponent = React.createClass({

  getInitialState : function(){
    return({
      value1: this.props.value1,
      value2: this.props.value2
    });
 },

...

});

If you’re moving from ES5 TO ES6 and creating React components using ES6 classes, if you try to follow the same approach you’ll see an error like this:

To set the initial state on an ES6 React class, you establish it in the constructor like this:

constructor(props) {
  super(props);
  this.state = {
    value1 : this.props.value1,
    value2 : this.props.value2,
  };
 }