Develop Reference

which data structure in java can hold hashmaps as its elements?

public static HashMap<String,Integer> users1 = new HashMap<>();
public static HashMap<String,Integer> users2 = new HashMap<>();
public static HashMap<String,Integer> users3 = new HashMap<>();
public static HashMap<String,Integer> users4 = new HashMap<>();
// Enter code here.
I need to add them into a arrayList or set or something and then they should be called when using that data structures index. Like is there any way to solve it

Or just simply use an array:
public static HashMap<String,Integer>[] users = HashMap<>[4];
users[0] = = new HashMap<>();
users[1] = = new HashMap<>();
users[2] = = new HashMap<>();
users[3] = = new HashMap<>();
And then use them:
users[0].add( "String", 123 );

you could as simply as :
List<HashMap<String, Integer>> list = new ArrayList<>();
// And then add them to list
list.add(users1);
list.add(users2);
...

ArrayList<HashMap> list = new ArrayList<>();
list.add(users1);

MultiList not displaying all result from webservice (Codename One)

Im trying to display some json records using a MultiList. I followed what was done here https://www.codenameone.com/manual/graphics.html but mine is returning only one record (Please see this image). The response came from this webservice
Below is my code. Please kindly show me where i'm wrong.
#Override
protected void beforeFormA(Form f) {
Style s = UIManager.getInstance().getComponentStyle("Button");
FontImage p = FontImage.createMaterial(FontImage.MATERIAL_PORTRAIT, s);
EncodedImage placeholder = EncodedImage.createFromImage(p.scaled(p.getWidth() * 3, p.getHeight() * 4), false);
getattractive();//fetch results from webservice and store inside response variable
ArrayList arr = (ArrayList) response.get("results");
for (Object m:arr){
Map ma = (Map)m;
address =(String) ma.get("formatted_address");
name=(String)ma.get("name");
icon=(String)ma.get("icon");
ArrayList<Map<String, Object>> data = new ArrayList<>();
data.add(createListEntry(name,address,icon));
DefaultListModel<Map<String, Object>> model = new DefaultListModel<>(data);
MultiList ml = new MultiList(model);
ml.getUnselectedButton().setIconName("icon_URLImage");
ml.getSelectedButton().setIconName("icon_URLImage");
ml.getUnselectedButton().setIcon(placeholder);
ml.getSelectedButton().setIcon(placeholder);
f.add(BorderLayout.CENTER, ml);
}
}
private Map<String, Object> createListEntry(String name, String addr, String coverURL) {
Map<String, Object> entry = new HashMap<>();
entry.put("Line1", name);
entry.put("Line2", addr);
entry.put("icon_URLImage", coverURL);
entry.put("icon_URLImageName", name);
return entry;

You should fix the indentation. The for loop encapsulates everything so you are looping over all the elements and for X elements you are adding X multi lists.
This is something you would instantly see if you step over the code with a debugger...

done. I moved the line below out of the method and place it inside the class.
ArrayList> data = new ArrayList<>();

Converting Java Map to Spark DataFrame (Java API)

I'm trying to use Spark (Java API) to take an in-memory Map (that potentially contains other nested Maps as its values) and convert it into a dataframe. I think I need something along these lines:
Map myMap = getSomehow();
RDD myRDD = sparkContext.makeRDD(myMap); // ???
DataFrame df = sparkContext.read(myRDD); // ???
But I'm having a tough time seeing the forest through the trees here...any ideas? Again this might be a Map<String,String> or a Map<String,Map>, where there could be several nested layers of maps-inside-of-maps-inside-of-maps, etc.

So I tried something, not sure if this is the most efficient option to do it, but I do not see any other right now.
SparkConf sf = new SparkConf().setAppName("name").setMaster("local[*]");
JavaSparkContext sc = new JavaSparkContext(sf);
SQLContext sqlCon = new SQLContext(sc);
Map map = new HashMap<String, Map<String, String>>();
map.put("test1", putMap);
HashMap putMap = new HashMap<String, String>();
putMap.put("1", "test");
List<Tuple2<String, HashMap>> list = new ArrayList<Tuple2<String, HashMap>>();
Set<String> allKeys = map.keySet();
for (String key : allKeys) {
list.add(new Tuple2<String, HashMap>(key, (HashMap) map.get(key)));
};
JavaRDD<Tuple2<String, HashMap>> rdd = sc.parallelize(list);
System.out.println(rdd.first());
List<StructField> fields = new ArrayList<>();
StructField field1 = DataTypes.createStructField("String", DataTypes.StringType, true);
StructField field2 = DataTypes.createStructField("Map",
DataTypes.createMapType(DataTypes.StringType, DataTypes.StringType), true);
fields.add(field1);
fields.add(field2);
StructType struct = DataTypes.createStructType(fields);
JavaRDD<Row> rowRDD = rdd.map(new Function<Tuple2<String, HashMap>, Row>() {
#Override
public Row call(Tuple2<String, HashMap> arg0) throws Exception {
return RowFactory.create(arg0._1, arg0._2);
}
});
DataFrame df = sqlCon.createDataFrame(rowRDD, struct);
df.show();
In this scenario I assumed that the Map in the Dataframe is of Type (String, String). Hope this helps!
Edit: Obviously you can delete all the prints. I did this for visualization purposes!

java assign map each value into an String array

I want to save data into master - details table.First portion is for master table and last portion is for details table.I have got java.lang.String cannot be cast to [Ljava.lang.String .How to recover from this problem.How to assign map.get("step_id[]") into a string array String[] WfIds. I want to assign each value into distinct string array.
Controller Code
Map<String,Object> wfManager = new HashMap<String,Object>();
//************************Master data sent from view******************************//
wfManager.put("workflow_code",(request.getParameter("workflow_code")).toUpperCase());
wfManager.put("workflow_name",request.getParameter("workflow_name"));
wfManager.put("workflow_descr",request.getParameter("workflow_descr"));
wfManager.put("object_type_code",request.getParameter("object_type_code"));
//*********************Detail item data sent from view********************************//
wfManager.put("wf_block_id[]", request.getParameter("wf_block_id[]"));
wfManager.put("step_code[]" , request.getParameter("step_code[]"));
wfManager.put("step_name[]", request.getParameter("step_name[]"));
wfManager.put("doa_type_code[]", request.getParameter("doa_type_code[]"));
wfManager.put("doa_type_name[]", request.getParameter("doa_type_name[]"));
Service Code
public Map<String, String> insert(Map<String, Object> map) {
//************************Master data sent from view******************************//
Map<String, String> data = new HashMap<String, String>();
Workflow wf = new Workflow();
wf.setWorkflowCode((String)map.get("workflow_code"));
wf.setWorkflowName((String)map.get("workflow_name"));
wf.setWorkflowDescr((String)map.get("workflow_descr"));
wf.setObjectTypeCode((String)map.get("object_type_code"));
String[] WfIds = (String[]) map.get("step_id[]");
String[] wfBlockIds = (String[]) map.get("wf_block_id[]");
String[] wfsCodes = (String[]) map.get("step_code[]");
String[] stepNames = (String[]) map.get("step_name[]");
String[] doaTypeCodes = (String[]) map.get("doa_type_code[]");
String[] doaTypeNames = (String[]) map.get("doa_type_name[]");
List<WorkflowDetails> wfDetailsList = new ArrayList<WorkflowDetails>();
for(int i = 0; i< wfsCodes.length; i++){
WorkflowDetails wfDetails = new WorkflowDetails();
wfDetails.setWorkflowCode(wf.getWorkflowCode());
wfDetails.setWorkflowName(wf.getWorkflowName());
wfDetails.setWorkflowDescr(wf.getWorkflowDescr());
wfDetails.setWorkflowObjectTypeCode(wf.getObjectTypeCode());
wfDetails.setWorkflowObjectTypeName(wf.getObjectTypeName());
wfDetailsList.add(i,wfDetails);
}
wf.setSteps(wfDetailsList);
id = workflowManagerDAO.insertDoc(wf);
data.put("id", id);
return data;
}
Code for DAO:
#Transactional
#Override
public String insertDoc(Workflow wfManager) {
for(int i = 0; i < wfManager.getSteps().size(); i++){
WorkflowDetails wfDetails = new WorkflowDetails();
wfDetails = wfManager.getSteps().get(i);
sessionfactory.getCurrentSession().save(wfDetails);
sessionfactory.getCurrentSession().flush();
}
String id = (String) sessionfactory.getCurrentSession().save(wfManager);
sessionfactory.getCurrentSession().flush();
return id;
}

If you absolutely need to use request.getParameter(), you will have to convert your arrays to strings using a delimiter character, e.g. convert this
String[] array = { "John", "Peter", "Paul" };
to this
String plainTextArray = "John#Peter#Paul";
Then you will be able to pass you array values as String (the only type that getParameter() understands).
You can then restore them like this
String[] restoredArray = request.getParameter("plainTextArray").split("#");
Maybe you want to have a look at setAttribute() and getAttribute() which let you store any objects (including arrays). You can start here Difference between getAttribute() and getParameter()

Replacing multimap with mapping an element to a collection of elements

I am trying to map a meterId to a list of MeterBlinks that have that Id. I'm mainly confused on how to build the list up for the HashMap.put() call. Code below:
Map<String, List<MeterBlink>> IdToMetersMap = new HashMap<>();
for (MeterBlink meterBlink : createData()) {
List<MeterBlink> meterBlinkList = new ArrayList<>();
meterBlinkList.add(meterBlink);
String meterId = meterBlink.getMeterId();
idToMetersMap.put(meterId, meterBlinkList)
}
I think the issue is that I am creating a new list each time I iterate through but I am not sure how to resolve this.

Use the computeIfAbsent method added in jre 8:
Map<String, List<MeterBlink>> idToMetersMap = new HashMap<>();
for (MeterBlink meterBlink : createData()) {
String meterId = meterBlink.getMeterId();
idToMetersMap.computeIfAbsent(meterId, k -> new ArrayList<>()).add(meterBlinks);
}
Another option in java 8:
Map<String, List<MeterBlink>> idToMetersMap = createData().stream()
.collect(Collectors.groupingBy(MeterBlink::getMeterId));

I like the java8 answer, but here without java8 (without lambda expressions):
Map<String, List<MeterBlink>> idToMetersMap = new HashMap<>();
for (MeterBlink meterBlink : createData()) {
String meterId = meterBlink.getMeterId();
List<MeterBlink> meterBlinkList = idToMetersMap.get(meterId);
//if List doesn't exist create it and put in Map
if (meterBlinkList == null) {
meterBlinkList = new ArrayList<>();
idToMetersMap.put(meterId, meterBlinksList)
}
meterBlinkList.add(meterBlink);
}