if else condition with Java Lamba – Howto

//lambda Predicate
private static Predicate<HttpStatus> isErrorCode = (HttpStatus statusCode) -> (statusCode.is5xxServerError() || statusCode.is4xxClientError());

//your method
public static Mono<ClientResponse> getResponse(ClientResponse clientResponse) {
        if (isErrorCode.test(clientResponse.statusCode())) {

Do not forget to checkout the BiPredicate as well 😉

Why Spring Webflux is better than HttpClient – HowTo in Java

A lot of Boilerplate Code can be avoided.

AND: it is reactive, non-blocking.

Example (really, an example) – the ‚old way‘:

        HttpPost request = new HttpPost("http://www.someurl.de");
        request.setHeader(HttpHeaders.ACCEPT, ContentType.APPLICATION_JSON.getMimeType());

        String json = someJsonConverter.toJson(someRequestDto);
        HttpEntity stringEntity = new StringEntity(json, ContentType.APPLICATION_JSON);

        try {
            CloseableHttpResponse response2 = httpclient.execute(request);

            if (HttpStatus.SC_CREATED != response2.getStatusLine().getStatusCode()) {
                //TODO eventually handle http statuus additionally
                return returnHandleAndDoNotThrow();
            SomeResponseDto responseDto = (SomeResponseDto) 
            return Optional.ofNullable(responseDto);
        } catch (IOException e) {
            return Optional.empty();;

The new way:

        Function<UriBuilder, URI> function = uriBuilder ->  
        return client.post()
                .body(Mono.just(someDtoInstance), SomeDto.class)
//any errors, status codes are handled by a filter which you can define as follows:


I am using Spring Boot for this, so I do have a Config class.

import ...
import org.springframework.context.annotation.Bean;
import reactor.core.publisher.Mono;
import org.springframework.web.reactive.function.client.ExchangeFilterFunction;
import org.springframework.web.reactive.function.client.WebClient;
import org.springframework.context.annotation.Configuration;

public class WebClientConfig {

    //Create the Bean for Autowiring
    public WebClient webClient() {
        return WebClient.builder().filter(someStatusHandlingFilter()).build();
    //Handle status codes
    public static ExchangeFilterFunction someStatusHandlingFilter() {
        return ExchangeFilterFunction.ofResponseProcessor(clientResponse -> {
            if ((clientResponse.statusCode().is4xxServerError() 
                || clientResponse.statusCode().is5xxClientError())) {
                return clientResponse                        
                        .flatMap(errorBody -> {
                            return Mono.error(someExceptionToLog);
            } else {
                return Mono.just(clientResponse);


            <version>your latest version goes here</version>
            <version>your latest version goes here</version>

Java Stream Custom Collector – Howto

Sometimes the commonly available Collectors are not what we need.
Here is one example for a Singleton Custom Collector:

public static <T> Collector<T, ?, T> singleton() {
    return Collectors.collectingAndThen(
            Collectors.toList(), list -> {
                if (list.size() != 1) {
                    // or log and return nil
                    throw new CustomException();
                return list.get(0);

//and use it:
        .filter(elem -> elem.getExampleAttribute() == 0).collect(singleton());

Howto generate a new SSH key pair

ssh-keygen -t ed25519 -C "email@example.com"

Note that in this example we use an ed25519 key.

The -c is providing a comment to divide the key amongst others.

I alwas use the suggested path and just klick enter 😉

How to run eslint in Terminal / Shell

npm install && npm i -g eslint && npx eslint --ext .tsx --ext .ts ./

Please heed that npm install is used here to start my React application, which uses it as a build tool. IMportant

npm i -g eslint will install eslint, if it does not exist yet (for example a CI with Jenkins).

The npx eventually executes eslint for all files with ending .tsx or .ts recursively in the current directory. Please adapt the endings according to your needs – when you do not use TypeScript but JavaScript change it to .js

How to check Typescript Code with ESLint in IntelliJ or Webstorm

In your package.json add this example config:

 "eslintConfig": {
    "parserOptions": {
      "parser": "babel-eslint",
      "sourceType": "module"
    "env": {
      "browser": true,
      "es6": true
    "globals": {
      "Vue": true
    "parser": "@typescript-eslint/parser",
    "plugins": [
    "extends": [
    "rules": {
      "quotes": [
          "avoidEscape": true
      "comma-dangle": [
          "arrays": "ignore",
          "objects": "always-multiline",
          "imports": "never",
          "exports": "never",
          "functions": "ignore"
      "arrow-parens": 0,
      "no-tabs": 0,
      "indent": [
          "SwitchCase": 1
      "no-console": 1,
      "generator-star-spacing": 0

In your IDE terminal, execute:

npm install @typescript-eslint/parser @typescript-eslint/eslint-plugin --save-dev

In IntelliJ settings, add:

From now on, when you open your .ts or .tsx files, the ESLint will detect the errors.

You can open the context menu then, by clicking the right mouse tab and click on „Fix ESlint Problems“.

IntelliJ will then automatically fix the problems.

How to create an NPM Package

You want reusable components, elements? Flexible structure?
Separation of concerns, decoupling in your JS Code?

A good strategy is to create an NPM Package.

  • Identify the code you would like to decouple.
  • create a new project
  • create an src folder
  • paste the JS or TS files in that folder
  • install the missing dependencies like Typescript, TSlint, Material UI
  • Write UNIT Tests to test your code before publishing it

I use JEST and to include the relevant Code, add this to your tsconfig.json:

    "include": ["src/**/*"],
    "exclude": ["node_modules", "**/__tests__/*"] 

Before the package is published, you can test it locally:

  • In your terminal, run npm link
  • This will compile and create a symbolic link, pointing to another directory/files on your development machine.
  • Now include the new package as a dependency. In your terminal, run npm link <module_name>
  • If everything can be imported and used, the test work and you are satisfied, perform npm unlink --nosave <module_name> on your main projects directory. This will remove the symbolic link.
  • Then run npm unlink to also remove the global link.

Now you have extracted and published Code as NPM package.

JUnit Test String contained / contains String

With the Hamcrest Matchers, do this:

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.core.StringContains.containsString;

assertThat(actualData, containsString(expectedData));