Accessing Instance Metadata

@SuppressWarnings("serial")
// With @WebServlet annotation the webapp/WEB-INF/web.xml is no longer required.
@WebServlet(name="Metadata",description="Metadata: Write info about GAE Standard",
urlPatterns="/metadata")
publicclass MetadataServletextendsHttpServlet{
privatefinalString[]metaPath={
"/computeMetadata/v1/project/numeric-project-id",// (pending)
"/computeMetadata/v1/project/project-id",
"/computeMetadata/v1/instance/zone",
"/computeMetadata/v1/instance/service-accounts/default/aliases",
"/computeMetadata/v1/instance/service-accounts/default/email",
"/computeMetadata/v1/instance/service-accounts/default/",
"/computeMetadata/v1/instance/service-accounts/default/scopes",
// Tokens work - but are a security risk to display
// "/computeMetadata/v1/instance/service-accounts/default/token"
};
finalString[]metaServiceAcct={
"/computeMetadata/v1/instance/service-accounts/{account}/aliases",
"/computeMetadata/v1/instance/service-accounts/{account}/email",
"/computeMetadata/v1/instance/service-accounts/{account}/scopes",
// Tokens work - but are a security risk to display
// "/computeMetadata/v1/instance/service-accounts/{account}/token"
};
privatefinalStringmetadata="http://metadata.google.internal";
privateTemplateEnginetemplateEngine;
// Use OkHttp from Square as it's quite easy to use for simple fetches.
privatefinalOkHttpClientok=newOkHttpClient.Builder()
.readTimeout(500,TimeUnit.MILLISECONDS)// Don't dawdle
.writeTimeout(500,TimeUnit.MILLISECONDS)
.build();
// Setup to pretty print returned json
privatefinalGsongson=newGsonBuilder()
.setPrettyPrinting()
.create();
privatefinalJsonParserjp=newJsonParser();
// Fetch Metadata
StringfetchMetadata(Stringkey)throwsIOException{
Requestrequest=newRequest.Builder()
.url(metadata+key)
.addHeader("Metadata-Flavor","Google")
.get()
.build();
Responseresponse=ok.newCall(request).execute();
returnresponse.body().string();
}
StringfetchJsonMetadata(Stringprefix)throwsIOException{
Requestrequest=newRequest.Builder()
.url(metadata+prefix)
.addHeader("Metadata-Flavor","Google")
.get()
.build();
Responseresponse=ok.newCall(request).execute();
// Convert json to prety json
returngson.toJson(jp.parse(response.body().string()));
}
@Override
publicvoidinit(){
// Setup ThymeLeaf
ServletContextTemplateResolvertemplateResolver=
newServletContextTemplateResolver(this.getServletContext());
templateResolver.setPrefix("/WEB-INF/templates/");
templateResolver.setSuffix(".html");
templateResolver.setCacheTTLMs(Long.valueOf(1200000L));// TTL=20m
// Cache is set to true by default. Set to false if you want templates to
// be automatically updated when modified.
templateResolver.setCacheable(true);
templateEngine=newTemplateEngine();
templateEngine.setTemplateResolver(templateResolver);
}
@Override
publicvoiddoGet(HttpServletRequestreq,HttpServletResponseresp)throwsIOException{
StringdefaultServiceAccount="";
WebContextctx=newWebContext(req,resp,getServletContext(),req.getLocale());
resp.setContentType("text/html");
Stringenvironment=
(String)System.getProperties().get("com.google.appengine.runtime.environment");
ctx.setVariable("production",environment);
// The metadata server is only on a production system
if(environment.equals("Production")){
TreeMap<String,String>m=newTreeMap<>();
for(Stringkey:metaPath){
m.put(key,fetchMetadata(key));
if(key.contains("default/email")){
defaultServiceAccount=m.get(key);
}
}
ctx.setVariable("Metadata",m.descendingMap());
m=newTreeMap<>();
for(Stringkey:metaServiceAcct){
// substitute a service account for {account}
key=key.replace("{account}",defaultServiceAccount);
m.put(key,fetchMetadata(key));
}
ctx.setVariable("sam",m.descendingMap());
// Recursivly get all info about service accounts -- Note tokens are leftout by default.
ctx.setVariable("rsa",
fetchJsonMetadata("/computeMetadata/v1/instance/service-accounts/?recursive=true"));
// Recursivly get all data on Metadata server.
ctx.setVariable("ram",fetchJsonMetadata("/?recursive=true"));
}
templateEngine.process("index",ctx,resp.getWriter());
}
}