Enabled Spring Boot banner while using JSON formatted logging using spring.main.banner-mode=LOG

JsonBannerDemo.java

package demo;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

@SpringBootApplication
class JsonBannerDemo {
    public static void main(String[] args) throws Exception {
        // prepares output capturing
        PrintStream oldOut = System.out;
        ByteArrayOutputStream capture = Stream.of(new ByteArrayOutputStream())
                .peek(out -> System.setOut(new PrintStream(out))).findAny().get();

        // runs Spring application with activated JSON logging and banner printed to log
        // so INGREDIENT #1: spring.main.banner-mode=log
        //    INGREDIENT #2: a logger capable of logging multi-line strings (e.g. JSON logger)
        SpringApplication.run(JsonBannerDemo.class, new String[]{
                "--spring.main.banner-mode=log"
        });

        // restores System.out, prints JSON log containing the escaped banner
        // and prints extracted unescaped banner
        System.setOut(oldOut);
        String bannerJsonLog = capture.toString().split(System.lineSeparator())[0];
        Map<String, Object> json = new ObjectMapper().readValue(bannerJsonLog, new TypeReference<Map<String, Object>>() {});
        String printedBanner = (String) json.get("message");
        System.out.println(Stream.of("JSON formatted log entry:", bannerJsonLog, "", "contains banner completely unchanged if you simply use spring.main.banner-mode=log", printedBanner).collect(Collectors.joining(System.lineSeparator())));
        System.exit(0);
    }
}

Spring Boot banner output does not need to be disabled for JSON formatted logging to work, as this gist shows.
The program has the following output:

JSON formatted log entry:
{"timestamp":"2020-04-09 02:35:58.703","level":"INFO","service":"JsonBannerDemo","logger":"org.springframework.boot.SpringApplication","thread":"main","message":"\n  .   ____          _            __ _ _\n /\\\\ / ___'_ __ _ _(_)_ __  __ _ \\ \\ \\ \\\n( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\\n \\\\/  ___)| |_)| | | | | || (_| |  ) ) ) )\n  '  |____| .__|_| |_|_| |_\\__, | / / / /\n =========|_|==============|___/=/_/_/_/\n\u001B[32m :: Spring Boot :: \u001B[39m      \u001B[2m (v2.2.5.RELEASE)\u001B[0;39m\n\n"}

contains banner completely unchanged if you simply use spring.main.banner-mode=log

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.5.RELEASE)

If set up correctly the logger should serialize the banner to:

  .   ____          _            __ _ _\n /\\\\ / ___'_ __ _ _(_)_ __  __ _ \\ \\ \\ \\\n( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\\n \\\\/  ___)| |_)| | | | | || (_| |  ) ) ) )\n  '  |____| .__|_| |_|_| |_\\__, | / / / /\n =========|_|==============|___/=/_/_/_/\n\u001B[32m :: Spring Boot :: \u001B[39m      \u001B[2m (v2.2.5.RELEASE)\u001B[0;39m

Even the ANSI formatting is correctly escaped.