Retrofit

Try it in 3 steps

1. 1

   Pin Retrofit 3.0.0 and its JSON converter

   Requires Java 17, Maven, Python 3, and curl. Create a POM with fixed dependencies in a temporary directory.

   retrofit_demo_dir=$(mktemp -d "${TMPDIR:-/tmp}/retrofit-demo.XXXXXX") && cd "$retrofit_demo_dir" && printf '%s ' '<project xmlns="http://maven.apache.org/POM/4.0.0"><modelVersion>4.0.0</modelVersion><groupId>demo</groupId><artifactId>retrofit-demo</artifactId><version>1</version><properties><maven.compiler.release>17</maven.compiler.release></properties><dependencies><dependency><groupId>com.squareup.retrofit2</groupId><artifactId>retrofit</artifactId><version>3.0.0</version></dependency><dependency><groupId>com.squareup.retrofit2</groupId><artifactId>converter-gson</artifactId><version>3.0.0</version></dependency></dependencies><build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.14.1</version></plugin></plugins></build></project>' > pom.xmlCopy
2. 2

   Compile a typed API interface

   In the same directory, define GET /message and its JSON model, resolve dependencies, and compile.

   mkdir -p src/main/java/demo && printf '%s ' 'package demo; import retrofit2.*; import retrofit2.converter.gson.*; import retrofit2.http.*; public class Main { record Message(String value){} interface Api{@GET("message") Call<Message> message();} public static void main(String[]a)throws Exception{var r=new Retrofit.Builder().baseUrl(a[0]).addConverterFactory(GsonConverterFactory.create()).build();var v=r.create(Api.class).message().execute().body();System.out.println(v.value());}}' > src/main/java/demo/Main.java && mvn -q dependency:copy-dependencies packageCopy
3. 3

   Convert a real localhost response

   Serve JSON from a directly owned loopback process and verify Retrofit converts it to typed-ok. The trap kills and waits for the PID on success or failure.

   ( set -eu; port=$(python3 -c 'import socket;s=socket.socket();s.bind(("127.0.0.1",0));print(s.getsockname()[1]);s.close()'); pid=''; cleanup(){ if [ -n "$pid" ];then kill "$pid" 2>/dev/null||true;wait "$pid" 2>/dev/null||true;fi;}; trap cleanup EXIT HUP INT TERM; printf '%s' '{"value":"typed-ok"}' > message; python3 -m http.server "$port" --bind 127.0.0.1 > server.log 2>&1 & pid=$!; i=0;until curl -fsS --max-time 1 "http://127.0.0.1:$port/message" >/dev/null;do i=$((i+1));[ "$i" -lt 20 ];sleep .25;done; out=$(java -cp 'target/classes:target/dependency/*' demo.Main "http://127.0.0.1:$port/");[ "$out" = typed-ok ];cleanup;pid='';python3 -c 'import errno,socket,sys;s=socket.socket();s.settimeout(1);r=s.connect_ex(("127.0.0.1",int(sys.argv[1])));raise SystemExit(0 if r==errno.ECONNREFUSED else 1)' "$port";trap - EXIT HUP INT TERM;printf '%s ' "$out" )Copy

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