in sample/src/main/java/org/apache/apisix/plugin/runner/filter/PostReqWithVarsFilter.java [50:62]
public void postFilter(PostRequest request, PostResponse response, PluginFilterChain chain) {
String configStr = request.getConfig(this);
Gson gson = new Gson();
Map<String, Object> conf = new HashMap<>();
conf = gson.fromJson(configStr, conf.getClass());
String bodyStr = request.getBody();
Map<String, Object> body = new HashMap<>();
body = gson.fromJson(bodyStr, body.getClass());
assert body.get("url").toString().endsWith((String) conf.get("rewrite_path"));
String serverPort = request.getVars("server_port");
response.setHeader("server_port", serverPort);
chain.postFilter(request, response);
}