Develop Reference

Usng StringJoiner in complex HashMaps

I have a list of Maps as below:
List<Map<String,Object>> someObjectsList = new ArrayList<Map<String,Object>>();
I am storing the following data in each HashMap
key value
2017-07-21 2017-07-21-07.33.28.429340
2017-07-24 2017-07-24-01.23.33.591340
2017-07-24 2017-07-24-01.23.33.492340
2017-07-21 2017-07-21-07.33.28.429540
I want to iterate through the list of HashMaps and check if the key matches with the first 10 characters of any of the HashMap value, then I want to store those keys and values in the following format. i.e. by using the telemeter 'comma'. The ultimate aim is to group the unique keys of the HashMaps and their relative values (if the key matches with the first 10 characters of any of the HashMap value) in a new HashMap.
key value
2017-07-21 2017-07-21-07.33.28.429340,2017-07-21-07.33.28.429540
2017-07-24 2017-07-24-01.23.33.591340,2017-07-24-01.23.33.492340
I am trying with following java code using StringJoiner, but not getting the results as expected. Any clue on how to frame the logic here?
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.StringJoiner;
public class SampleOne {
public static void main(String[] args) {
// TODO Auto-generated method stub
List<Map<String, Object>> someObjectsList = new ArrayList<Map<String, Object>>();
Map<String, Object> mapOne = new HashMap<String, Object>();
mapOne.put("2017-07-21", "2017-07-21-07.33.28.429340");
Map<String, Object> mapTwo = new HashMap<String, Object>();
mapTwo.put("2017-07-24", "2017-07-24-01.23.33.591340");
Map<String, Object> mapThree = new HashMap<String, Object>();
mapThree.put("2017-07-24", "2017-07-24-01.23.33.492340");
Map<String, Object> mapFour = new HashMap<String, Object>();
mapFour.put("2017-07-21", "2017-07-21-07.33.28.429540");
someObjectsList.add(mapOne);
someObjectsList.add(mapTwo);
someObjectsList.add(mapThree);
someObjectsList.add(mapFour);
for (Map map : someObjectsList) {
StringJoiner sj = new StringJoiner(",");
for (Object key : map.keySet()) {
String value = ((String) map.get(key));
String date = value.substring(0, Math.min(value.length(), 10));
//System.out.println(str);
//System.out.println(value);
if(key.equals(date)) {
sj.add(value);
System.out.println(sj.toString());
}
}
}
}
}
output:
2017-07-21-07.33.28.429340
2017-07-24-01.23.33.591340
2017-07-24-01.23.33.492340
2017-07-21-07.33.28.429540

Make use of the .merge function:
Map<String, Object> finalMap = new HashMap<String, Object>();
for (Map map : someObjectsList) {
for (Object key : map.keySet()) {
String value = ((String) map.get(key));
finalMap.merge((String) key, value, (k, v) -> k + "," + v);
}
}
which outputs:
{2017-07-21=2017-07-21-07.33.28.429340,2017-07-21-07.33.28.429540,
2017-07-24=2017-07-24-01.23.33.591340,2017-07-24-01.23.33.492340}
The same can be achieved by the following one-liner:
someObjectsList.stream()
.flatMap(i -> i.entrySet().stream())
.collect(Collectors.toMap(Entry::getKey, Entry::getValue,
(k, v) -> k + "," + v));

On your code, you are using different StringJoiner on each map. So, it's creating a new instance of it.
You can save your keys on a map. An example code:
(Edit: I did not remove your StringJoiner part.)
public static void main(String[] args) {
// TODO Auto-generated method stub
List<Map<String, Object>> someObjectsList = new ArrayList<Map<String, Object>>();
Map<String, Object> mapOne = new HashMap<String, Object>();
mapOne.put("2017-07-21", "2017-07-21-07.33.28.429340");
Map<String, Object> mapTwo = new HashMap<String, Object>();
mapTwo.put("2017-07-24", "2017-07-24-01.23.33.591340");
Map<String, Object> mapThree = new HashMap<String, Object>();
mapThree.put("2017-07-24", "2017-07-24-01.23.33.492340");
Map<String, Object> mapFour = new HashMap<String, Object>();
mapFour.put("2017-07-21", "2017-07-21-07.33.28.429540");
someObjectsList.add(mapOne);
someObjectsList.add(mapTwo);
someObjectsList.add(mapThree);
someObjectsList.add(mapFour);
Map<String, Object> outputMap = new HashMap<String, Object>();
for (Map map : someObjectsList) {
StringJoiner sj = new StringJoiner(",");
for (Object key : map.keySet()) {
String value = ((String) map.get(key));
String date = value.substring(0, Math.min(value.length(), 10));
//System.out.println(str);
//System.out.println(value);
if(key.equals(date)) {
sj.add(value);
System.out.println(sj.toString());
if(outputMap.containsKey(key)) {
String str = (String) map.get(key);
str = str + "," + value;
outputMap.put((String)key, str);
} else {
outputMap.put((String)key, value);
}
}
}
}
for (String map : outputMap.keySet()) {
System.out.println(map + " " + outputMap.get(map));
}
}

You are looking for the grouping behavior of processing a List. You can use the advantage of java-stream since java-8. In any case, you need a new Map to store the values in order to print them. :
someObjectsList.stream()
.flatMap(i -> i.entrySet().stream()) // flatmapping to entries
.collect(Collectors.groupingBy(Entry::getKey)) // grouping them using the key
In case you want to use for-loops. In this case it is harder since the more entries might appear in each List item:
final Map<String, List<Object>> map = new HashMap<>();
for (Map<String, Object> m: someObjectsList) { // iterate List<Map>
for (Entry<String, Object> entry: m.entrySet()) { // iterate entries of each Map
List<Object> list;
final String key = entry.getKey(); // key of the entry
final Object value = entry.getValue(); // value of the entry
if (map.containsKey(key)) { // if the key exists
list = map.get(key); // ... use it
} else {
list = new ArrayList<>(); // ... or else create a new one
}
list.add(value); // add the new value
map.put(key, list); // and add/update the entry
}
}
Printing out of Map<String, List<Object>> map in both cased will produce the following output:
2017-07-21=[2017-07-21-07.33.28.429340, 2017-07-21-07.33.28.429540],
2017-07-24=[2017-07-24-01.23.33.591340, 2017-07-24-01.23.33.492340]

Any reason you're using Object over String and avoiding safety checks? That said, it's not "the first 10 characters", you want to see if value starts with key full-stop (all your keys are 10 characters). So in that case you can just do if (value.startsWith(key)) { ... }. Don't forget your newlines if the stringjoiner wasn't full. Lastly, you don't need a List, a Map can hold multiple keys at once. An alternative way of doing it:
//LinkedHashMap will preserve our insertion order
Map<String, String> map = new LinkedHashMap<>();
map.put("2017-07-21", "2017-07-21-07.33.28.429340");
map.put("2017-07-24", "2017-07-24-01.23.33.591340");
//note duplicates are overwritten, but no value change here
map.put("2017-07-24", "2017-07-24-01.23.33.492340");
map.put("2017-07-21", "2017-07-21-07.33.28.429540");
// You can also use Java 8 streams for the concatenation
// but I left it simple
List<String> matches = map.entrySet()
.filter(e -> e.getValue().startsWith(e.getKey())
.collect(Collectors.toList());
String concatenated = String.join("\n", matches);
If you wanted to generate that string without streams, it would look like this (again, not using #entrySet for simplicity, but it would be more efficient here):
List<String> matches = new ArrayList<>();
StringJoiner joiner = new StringJoiner("\n");
for (String key : map.keySet()) {
String value = map.get(key);
if (value.startsWith(key)) {
joiner.add(value);
}
}
//joiner#toString will give the expected result

How to merge two ArrayList<Map<String, String>> to one?

ArrayList<Map<String, String>> result1
result1 is like
(1, a)
(2, a)
(3, b)
(4, e)
(5, e)
ArrayList<Map<String, String>> result2
result2 is like
(1,android)
(2,ios)
(3,android)
(4,android)
(5,ios)
I want to merge the two maps to build a map like this one
(1, ( a, android))
(2, ( a, ios))
(3, ( b, android))
(4, (e, android))
(5, (e, ios))
How to make this happen?

You can merge two streams with Stream.concat() and group them with Collectors.groupingBy() and Collectors.mapping():
Map<String, String> first = Map.of("1", "a", "2", "a");
Map<String, String> second = Map.of("1", "android", "2", "ios");
Map<String, List<String>> result = Stream.concat(first.entrySet().stream(), second.entrySet().stream())
.collect(groupingBy(Entry::getKey, mapping(Entry::getValue, toList())));
System.out.println(result);
will output:
{1=[a, android], 2=[a, ios]}

For the requirement you have specified here, you can do it like this.
I'm iterating over the keys of the first map. And collecting values for each key from all the maps and putting them in a list. Then put the list to the resulting map.
import java.util.*;
public class MergeMaps
{
public static void main(String[] args)
{
Map<String, String> map1 = new HashMap<>();
map1.put("1", "a");
map1.put("2", "a");
map1.put("3", "b");
map1.put("4", "e");
map1.put("5", "e");
Map<String, String> map2 = new HashMap<>();
map2.put("1", "android");
map2.put("2", "ios");
map2.put("3", "android");
map2.put("4", "android");
map2.put("5", "ios");
Set<String> keys = new HashSet<>();
keys.addAll(map1.keySet());
keys.addAll(map2.keySet());
Map<String, List<String>> mergedMap = new HashMap<>();
for (String key : keys)
{
List<String> list = new ArrayList<>();
list.add(map1.get(key));
list.add(map2.get(key));
mergedMap.put(key, list);
}
System.out.println(mergedMap);
}
}
Output will be:
{1=[a, android], 2=[a, ios], 3=[b, android], 4=[e, android], 5=[e, ios]}

You can try this approach as well:
Map<String, String> result1 = new HashMap<>();
// initialize result1 ...
Map<String, String> result2 = new HashMap<>();
// initialize result2 ...
Map<String, Map<String, String>> mergedResult = new HashMap<>();
Up to Java 8
result1.forEach((k1, v1) ->
mergedResult.put(k1, new HashMap<String, String>() {{
put(v1, result2.get(k1));
}}));
Java 9 or later
result1.forEach((k1, v1) -> mergedResult.put(k1,
Map.of(v1, result2.get(k1))));

This is one way arriving at the result:
Input Data:
// The first list of data
List<Map<String, String>> list1 = new ArrayList<>();
list1.add(getMapData("1", "a"));
list1.add(getMapData("2", "a"));
list1.add(getMapData("3", "b"));
list1.add(getMapData("4", "e"));
list1.add(getMapData("5", "e"));
list1.add(getMapData("999", "x"));
System.out.println(list1);
Data 1: [{1=a}, {2=a}, {3=b}, {4=e}, {5=e}, {999=x}]
// The second list of data
List<Map<String, String>> list2 = new ArrayList<>();
list2.add(getMapData("1", "android"));
list2.add(getMapData("2", "ios"));
list2.add(getMapData("3", "android"));
list2.add(getMapData("4", "android"));
list2.add(getMapData("5", "ios"));
list2.add(getMapData("888", "zzzzz"));
System.out.println(list2);
Data 2: [{1=android}, {2=ios}, {3=android}, {4=android}, {5=ios}, {888=zzzzz}]
// utility method for creating test data
private static Map<String, String> getMapData(String k, String v) {
Map<String, String> m = new HashMap<>();
m.put(k, v);
return m;
}
The Result Process:
The output is stored to a Map<String, List<String>>:
Map<String, List<String>> result = new HashMap<>();
// process the first list
for (Map<String, String> m : list1) {
for (Map.Entry<String, String> entry : m.entrySet()) {
List<String> valueList = new ArrayList<>();
valueList.add(entry.getValue());
result.put(entry.getKey(), valueList);
}
}
// process the second list; merge with the first
for (Map<String, String> m : list2) {
for (Map.Entry<String, String> entry : m.entrySet()) {
String k = entry.getKey();
List<String> valueList = result.get(k);
if (valueList == null) {
valueList = new ArrayList<>();
}
valueList.add(entry.getValue());
result.put(k, valueList);
}
}
System.out.println(result);
The Result:
{1=[a, android], 2=[a, ios], 3=[b, android], 4=[e, android], 5=[e, ios], 888=[zzzzz], 999=[x]}

How to Compare 2 LinkedHashMap and get difference in keys & values?

There are 2 LinkedHashMaps. I have to check if both LinkedHashMaps have same keys & values. If one LinkedHashMap contains extra keys + values then it should get printed or stored in 3rd LinkedHashMap. If any of the key or value is different in 2nd LinkedHashMap then it should be notified (print in console)
Eg
Map1 contains {A-a, B-b, C-c}
Map2 contains {A-a, B-r, C-c, Z-z}
So here 3rd LinkedHashMap should contain {Z-z} as it contains extra key and
{B-r} should get printed as it is modified

you can use this class :)
public class MapCompare {
private LinkedHashMap<String, String> differencesMap;
private LinkedHashMap<String, String> extraMap;
private void main(LinkedHashMap<String, String> map1, LinkedHashMap<String, String> map2) {
this.differencesMap = new LinkedHashMap<>();
this.extraMap = new LinkedHashMap<>();
Set<Map.Entry<String, String>> set1 = ((LinkedHashMap<String, String>) map1.clone()).entrySet();
Set<Map.Entry<String, String>> set2 = ((LinkedHashMap<String, String>) map2.clone()).entrySet();
set1.removeAll(set2);
compare(set1, map2);
set1 = map1.entrySet();
set2.removeAll(set1);
compare(set2, map1);
}
private LinkedHashMap<String, String> getDifferencesMap() {
return differencesMap;
}
private LinkedHashMap<String, String> getExtraMap() {
return extraMap;
}
private void compare(Set<Map.Entry<String, String>> set, LinkedHashMap<String, String> map) {
for (Map.Entry<String, String> entry : set) {
String key = entry.getKey();
String value = entry.getValue();
if (map.containsKey(key) || map.containsValue(value)) {
differencesMap.put(key, value);
} else {
extraMap.put(key, value);
}
}
}
public static void main(String[] args) {
LinkedHashMap<String, String> map1 = new LinkedHashMap<>();
map1.put("A", "a");
map1.put("B", "b");
map1.put("C", "c");
LinkedHashMap<String, String> map2 = new LinkedHashMap<>();
map2.put("A", "a");
map2.put("C", "c");
map2.put("B", "r");
map2.put("Z", "z");
MapCompare mapCompare = new MapCompare();
mapCompare.main(map1,map2);
System.out.println("diff: " + mapCompare.getDifferencesMap());
System.out.println("extra: " + mapCompare.getExtraMap());
}
}

Filter object from List if filter condition is multiple and coming dynamically

I have a requirement where I have to filter object from list based on multiple dynamic filter condition.
I have already written code by looping over objects and then all filter and returning false if any condition doesn't match. The code that I have written is as
Map<String, String> obj1 = new HashMap<>();
obj1.put("id", "1");
obj1.put("name", "name1");
obj1.put("dept", "IT");
obj1.put("sex", "M");
Map<String, String> obj2 = new HashMap<>();
obj2.put("id", "2");
obj2.put("name", "name2");
obj2.put("dept", "IT");
obj2.put("sex", "M");
Map<String, String> obj3 = new HashMap<>();
obj3.put("id", "3");
obj3.put("name", "name3");
obj3.put("dept", "DEV");
obj3.put("sex", "F");
ArrayList<Map<String, String>> employees = new ArrayList<>(Arrays.asList(obj1,obj2,obj3));
Map<String, String> filterCondition = new HashMap<>();
filterCondition.put("dept", "IT");
filterCondition.put("sex", "M");
List<Map<String, String>> filteredEmployee = new ArrayList<>();
for(Map<String,String> employee:employees){
if(isValid(filterCondition, employee)){
filteredEmployee.add(employee);
}
}
System.out.println(filteredEmployee);
isValid method is as
private static boolean isValid(Map<String, String> filterCondition, Map<String, String> employee) {
for(Entry<String, String> filterEntry:filterCondition.entrySet()){
if(!employee.get(filterEntry.getKey()).equals(filterEntry.getValue())){
return false;
}
}
return true;
}
Is there any better way to achieve it if filters that I am getting is coming dynamically.
I have already seen some answer in stackoverflow as here ,but with no help

Combine all filters as a single Predicate (using stream, reduce, and predicate composition):
Predicate<Map<String, String>> allConditions = filterCondition
.entrySet()
.stream()
.map(ThisClass::getAsPredicate)
.reduce((employee) -> true, Predicate::and);
Then just use Stream.filter()
List<Map<String, String>> filteredEmployees = employees
.stream()
.filter(allConditions)
.collect(Collectors.toList());
Helper function:
private static Predicate<Map<String, String>> getAsPredicate(Map.Entry<String, String> filter) {
return (Map<String, String> employee) -> employee.get(filter.getKey()).equals(filter.getValue());
}

Maybe you can use for-loop with Stream:
Stream<Map<String, String>> employeeStream = employees.stream();
for (Map.Entry<String, String> entry : filterCondition.entrySet()) {
employeeStream = employeeStream.filter(map -> entry.getValue()
.equals(map.get(entry.getKey())));
}
List<Map<String, String>> filteredEmployee = employeeStream.collect(Collectors.toList());

Compare map key with a list of strings

can map be compare with arraylist of string in java
private Map<String, String> checkInScopeLobs(Map<String, String> allLobsChkBx)
{
Map<String, String> inScopeLobs = new HashMap<String, String>();;
for (Map.Entry<String, String> entry : allLobsChkBx.entrySet())
{
if(entry.getKey().contains("1") || entry.getKey().contains("2") || entry.getKey().contains("3")){
inScopeLobs.put(entry.getKey(), entry.getValue());
}
}
return inScopeLobs;
}
is this a correct way ?

You can make use of keySet(). This method returns a Set of keys (for more info, Docs from Oracle about Map). This means less overhead than iterating over your whole map. In the following case you'll only request values of matching keys.
There are some other faults like a double semicolon and since JDK7 you don't have to define your map when initializing.
private Map<String, String> checkInScopeLobs(Map<String, String> allLobsChkBx) {
Map<String, String> inScopeLobs = new HashMap();
List<String> keys = Arrays.asList( { "1", "2", "3" } );
for(String key : allLobsChkBx.keySet()) {
if(keys.contains(key)) {
inScopeLobs.put(key, allLobsChkBx.get(key));
}
}
return inScopeLobs;
}
Why aren't you using an Integer instead of a String, since you're only storing numbers.

Since key is String you can use matches method from String class
for (Map.Entry<String, String> entry : allLobsChkBx.entrySet())
{
if(entry.getKey().matches(".*[123].*")){
inScopeLobs.put(entry.getKey(), entry.getValue());
}
}

Actually there are no such methods, but you can try this approach:
Map<String, String> allLobsChkBx = new HashMap<String, String>(4);
allLobsChkBx.put("1", "A");
allLobsChkBx.put("2", "B");
allLobsChkBx.put("3", "C");
allLobsChkBx.put("4", "D");
allLobsChkBx.put("5", "E");
System.out.println("Before retain: " + allLobsChkBx);
List<String> keysToRetain = Arrays.asList(new String[] { "1", "2", "3" });
allLobsChkBx.keySet().retainAll(keysToRetain);
System.out.println("After retain: " + allLobsChkBx);
It will produce following output:
Before retain: {3=C, 2=B, 1=A, 5=E, 4=D}
After retain: {3=C, 2=B, 1=A}