java - Retrofit2.0 - how to POST image along with some parameters -

i've been trying send image file parameters user_id, using retrofit, okhttp, gson, , rxandroid.

the problem following error:

500 internal server error

i can't upload file server. should change?

here's code.

homeactivity.java

    gson gson = new gsonbuilder()                 .setfieldnamingpolicy(fieldnamingpolicy.lower_case_with_underscores)                 .registertypeadapter(date.class, new datetypeadapter())                 .excludefieldswithoutexposeannotation()                 .create();      retrofit retrofit = new retrofit.builder()                 .baseurl(base_url)                 .addconverterfactory(gsonconverterfactory.create(gson))                 .addcalladapterfactory(rxjavacalladapterfactory.create())                 .build();      userapi uapi = retrofit.create(userapi.class);      file file = new file("sdcard/dcim/camera/img_20131129_123723.jpg");     requestbody filebody = requestbody.create(mediatype.parse("image/jpeg"), file);      map<string, object> map = new hashmap<>();     map.put("user_id", /*some string*/);     map.put("tweet_id", /*some numbers*/);     map.put("tweet_type", /*some numbers*/);      this.subscription = uapi.postimage(map, filebody)                 .subscribeon(schedulers.io())                 .observeon(androidschedulers.mainthread())                 .subscribe(new observer<tweet>() {                     @override                     public void onnext(tweet tweet) {}                      @override                     public void oncompleted() {}                      @override                     public void onerror(throwable e) {                         e.printstacktrace();                     }                 }); 

userapi.java

@headers("content-type: multipart/form-data") @multipart @post("static/write.json") public observable<tweet> postimage(        @part("params") map map,        @part("file\";filename=\"img_20131129_123723.jpg") requestbody file ); 

i tried append headers request myself, didn't work , same error before.

    multipartbody mb = new multipartbody.builder("boundary")                 .addpart(headers.of("content-disposition","file; filename=\"img_20131129_123723.jpg\"; name=\"img_20131129_123723.jpg\""), uploadfile)                 .addpart(paramsbody)                 .build();      request request = new request.builder()             .url("")             .post(mb)             .build(); 

build.gradle

dependencies {     compile filetree(dir: 'libs', include: ['*.jar'])     testcompile 'junit:junit:4.12'     compile 'com.android.support:appcompat-v7:23.0.1'     compile 'com.google.code.gson:gson:2.4'     compile 'com.squareup.retrofit2:retrofit:2.0.0-beta3'     compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta3'     compile 'com.squareup.retrofit2:adapter-rxjava:2.0.0-beta3'     compile 'com.squareup.okhttp3:okhttp:3.0.0'     compile 'io.reactivex:rxandroid:0.24.0'     compile 'io.reactivex:rxjava:1.1.0' } 

could please me?