We also cover some basic statistics you can use with groupingBy. first grouped by the fruit's name and then by the fruit's amount. He is interested in everything related to Java and the Spring framework. JCGs (Java Code Geeks) is an independent online community focused on creating the ultimate Java to Java developers resource center; targeted at the technical architect, technical team lead (senior developer), project manager and junior developers alike. Application Architecture Design Principles, Grouping and Aggregations With Java Streams, The download stream from the initial grouping that we convert into a list (using, Finisher function (lines 49) where we use a lambda expression to create two different streams from the previous list to do the aggregations and return them combined in a new, The first parameter is a lambda expression to generate the keys of the map. We use them for grouping objects by some property and storing results in a Map instance. and to get some basic statistics. Normally these are available in SQL databases. The examples in this post will use the Fruit class you can see below. have a more readable output in the console. See the original article here: Java 8 Streams Group By Multiple Fields with Collectors.groupingBy(). It has a substantial value because it is one of the most frequent ways to aggregate data, especially when combined with the different overloaded versions of groupingBy(), which also allows you to group items concurrently by utilising concurrent Collectors. Some examples are addition, averages, or max/min values. That are, using a chained comparator . The examples in this post will use the Fruit class you can see below. A guide to group by two or more fields in java 8 streams api. We'll assume that the reader has a basic understanding of Java Streams and the utility Collectors class. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I have splitted it into two methods for readability: Now we have three nested maps containing each list of persons: The Java 8 Collectors API provides us with an easy way to group our collections. Hi Stach,When you say final, are these static fields? In this article, we are going to show a straightforward path to solve these kinds of problems using Java Streams. Please read and accept our website Terms and Privacy Policy to post a comment. Let's start with grouping by one field. Stream Grouping. to get away from possible un-intentional duplicates because of String concat, you could use: Thanks for contributing an answer to Stack Overflow! Opinions expressed by Java Code Geeks contributors are their own. However, there are more sophisticated aggregations like weighted averages, geometric means. - Automate multiple technology migration activities in the Data . What if we want to compute an aggregate of a field value? In this program, we have gathered the count of employees but rather than this we can get the list of Employees. Practicing hands-on exercises is a quick way to master a new skill. We'll make it very generic so we can easily generalize it. What are the differences between a HashMap and a Hashtable in Java? Opinions expressed by DZone contributors are their own. You may even use the new Stream API to perform aggregate functions like sum(), count(), max(), and min() in specific groups, as shown in my previous streams examples. Aggregation of these individual fields can be easily done using Java Streams and . Java8Example1.java. For the downstream, we use Collectors::summingInt which returns a Collector that sums the number of tax entries that we get for each grouped element. That means if name + value + key is the same this is duplicate. Well, with Java 8 streams operations, you are covered for some of these. The code becomes, inefficient, very repetitive, and less than desirable. As we did in the previous section, we define a class that encapsulates the aggregation: It might seem surprising at first, but a straightforward solution to groupings that are followed by simple aggregations is to use Collectors::toMap. Thanks! how to perform Group By in java 8 with Collectors API? . @Michael I can not agree more, good comment. When you print the map you can see the count, sum, min, average, and max value for each of the groups. In this video we will create a group chat using Java sockets. In an illustration of a simple usage of groupingBy(), we show how to group the data by year. This can be easily generalized to solve more complex problems. To get the list, we should not pass the second argument for the second, Let us create the separate class with the group by properties and write implementation for equals(), hashcode() methods for. In the input list, the word Hello is repeated 5 times, Raj is for 2 times and reaming are for 1 time. each 'key,value' Grouping by a Map value in Java 8 using streams, In this article . Welcome to WittCode! We'll follow it more in detail: We see that this implementation not only allows us to do multiple field aggregations simultaneously but can also perform complex calculations in several stages. There are multiple services implemented in the Private Banking sector to provide and maintaining multiple bank officer in role of Banker , Investor etc to the prospect or client who might be an individual or part of the group in the Private banking. Examples Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation. Yes, true. Create objects for Stock class and add them to the List. reduce() method is a terminal operation which means reduce() method produces the result from stream and this should be called at the end of the stream.. reduce() method takes the two numbers such as number 1 and number 2. Please mail your requirement at [emailprotected] Duration: 1 week to 2 week. Blu-ray (Blu-ray Disc or BD), is a digital optical disc data storage format. To go on with a broken solution? Additionally, there might be the need to do simultaneous aggregations of several fields. We can also sum all the fields in a group. 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The toString method is overridden to When you get the initial item for a new group, you make a list and add it to the list, but if the group already exists in Map, you just fetch it and add your element to it. The common aggregate operations are: filter, map, reduce, find, match, and sort. Java's Streams API is a powerful and versatile tool for processing data. You only have to pass The groups formed by the Java 7 and Java 8 examples are identical. It is similar to a "group by" clause in SQL. After sorting them by city, you can see that they each have their own list; there is one employee in the Udaipur list, three in the Delhi list, and two in the Banglore list. Java Stream - limit() With Examples; Java Stream - distinct() With Examples; Reduction Operations in Java Stream API; Parallel Stream in Java . We use TaxEntry::getCity as the classifier function. To establish a group of different criteria in the previous edition, you had to write the same 5 to 6 lines of code. This invocation collects the values into a Set which has no ordering. This is the list of fruits we will use for the examples. There are several ways to do this, but a very straightforward approach is first to define: Notice that were using a Java record, which is a concise way to define an immutable class. That means inner aggregated Map value type should be List. final Map>> personsByCountryAndCity = persons.stream().collect( Later, it is divided into three groups based on their age, and as shown we have three groups for distinct age groups, 21, 23, and 31. Continuous upskilling knowledge to keep updated with the IT and new age technologies mainly in the stream of Cloud. Primary Skills: Providing infrastructure solutions based on Amazon web services (AWS) in a fast-paced, challenging, innovative company focused on reliability and . What if we want to compute an aggregate of a field value? To retrieve values in the same order in which they were placed into the Set, use a LinkedHashSet as shown below (only the relevant portion shown): Forget about collecting the results into a List or Set ot whatever. Explanation of the code. Normally these are available in SQL databases. Spellcaster Dragons Casting with legendary actions? Furthermore, I have developed multiple technical, communication, and analytical skills. How to determine chain length on a Brompton? His research interests were mainly focus on correctness verification and performance evaluation of realtime reactive systems . All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners. We create a List in the groupingBy() clause to serve as the key of the map. Group By, Count and Sort. Please add setters and getters. ORDER BY. When a stream executes in parallel, the Java runtime partitions the stream into multiple substreams. Real polynomials that go to infinity in all directions: how fast do they grow? It's as simple as passing the grouping condition to the collector and it is complete. 2. Things are a little more complicated if we try to find compound groupings. By simply modifying the grouping condition, you can create multiple groups. From the output, you can clearly observe that we can see the count by designation and gender type. Look at the below examples, you will see the code with the groupingBy() is used twice. Over 2 million developers have joined DZone. The following code shows how to group people by gender and How to convert a Java 8 Stream to an Array? For instance: . 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Lets consider a simple example that will highlight the challenges that we have mentioned in the previous section. function,1,JavaScript,1,jQuery,1,Kotlin,11,Kotlin Conversions,6,Kotlin Programs,10,Lambda,2,lang,29,Leap Year,1,live updates,1,LocalDate,1,Logging,1,Mac OS,3,Math,1,Matrix,6,Maven,1,Method References,1,Mockito,1,MongoDB,3,New Features,1,Operations,1,Optional,6,Oracle,5,Oracle 18C,1,Partition,1,Patterns,1,Programs,1,Property,1,Python,2,Quarkus,1,Read,1,Real Time,1,Recursion,2,Remove,2,Rest API,1,Schedules,1,Serialization,1,Servlet,2,Sort,1,Sorting Techniques,8,Spring,2,Spring Boot,23,Spring Email,1,Spring MVC,1,Streams,31,String,61,String Programs,28,String Revese,1,StringBuilder,1,Swing,1,System,1,Tags,1,Threads,11,Tomcat,1,Tomcat 8,1,Troubleshoot,26,Unix,3,Updates,3,util,5,While Loop,1, JavaProgramTo.com: Java 8 - Stream Group By - Collectors.GroupingBy() Examples, Java 8 - Stream Group By - Collectors.GroupingBy() Examples, https://blogger.googleusercontent.com/img/a/AVvXsEh_RPLbx0oq_t-161648gsqp_Lgg9NeCnthhux2lrYPPKymlU97yvT0fbFWotIViDj6SGZeG7Hcz7dx3hE53mIUEs5U5N9AB8MNV8_wZ76A5AfiRIGcNr7VFtWm0PC5M-8bdUak6MBKZxOvBp-shfek0Or1KPZCxNoeToBoHfZ2hmF00UDziEUeNfrd=w400-h214, https://blogger.googleusercontent.com/img/a/AVvXsEh_RPLbx0oq_t-161648gsqp_Lgg9NeCnthhux2lrYPPKymlU97yvT0fbFWotIViDj6SGZeG7Hcz7dx3hE53mIUEs5U5N9AB8MNV8_wZ76A5AfiRIGcNr7VFtWm0PC5M-8bdUak6MBKZxOvBp-shfek0Or1KPZCxNoeToBoHfZ2hmF00UDziEUeNfrd=s72-w400-c-h214, https://www.javaprogramto.com/2021/02/%20java-8-groupingby-collector.html, Not found any post match with your request, STEP 2: Click the link on your social network, Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy, Java 8 Sort on Multiple Fields with Comparator, Java 8 Examples Programs Before and After Lambda, Java 8 Lambda Expressions (Complete Guide), Java 8 Lambda Expressions Rules and Examples, Java 8 Accessing Variables from Lambda Expressions, Java 8 Default and Static Methods In Interfaces, interrupt() VS interrupted() VS isInterrupted(), Create Thread Without Implementing Runnable, Create Thread Without Extending Thread Class, Matrix Multiplication With Thread (Efficient Way). classifier function generates the keys in the map. Collections.frequency (list, i) Then for each element in the collection list, if the frequency of any element is more than one, then this element is a duplicate element. Notice that we are doing a multifield aggregation using BigDecimal. It represents a baseball player. The below examples are implemented as described and suggested way. We could accomplish this with a for loop, checking each individual, and placing them on a list of HashMaps with the same city, but in Java 8, you don't have to hack your way around like that; you have a far simpler alternative. The getters and setters are left out to make it more readable. By definition, a streaming operation is a single iteration through a set of data. Java Stream grouping by multiple fields Raw Collection8Utils.java This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. Create argument constructor and setter, getters methods for all properties. However, sometimes we want to process parts of the stream differently and get more than one set of results. This invocation collects the values into a Set which has no ordering. Grouping by multiple fields is a little bit more involved because the result map is keyed by the list of fields selected. 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Connect and share knowledge within a single location that is structured and easy to search. In this article, We have seen how to work with the multiple fields in group by using Collectors.groupingBy() method. Container Security: Top 5 Best Practices for DevOps Engineers, The Ultimate API Development Guide: Strategy, Tools, Best Practices. In this example we are going to group all persons in the collection by their country: If we take a look into the map, we can see how each country contains a list of its citizens: The result shows persons living in the specified country: In this example, we will group not only by country but also by city. Look at the below examples, you will see the code with the. How to do it if I have a class with public final fields and no getters? To begin untangling this issue, we take a cue from the previous aggregation and define a record that encapsulates all the fields that need to be aggregated: Now, how do we do the aggregation simultaneously for the two fields? Opinions expressed by DZone contributors are their own. 2. It was invented and developed in 2005 and released worldwide on June 20, 2006. Find your next career today! as key and a list of fruits as the value. - DevOps Lead for Federated Data Engineering, enabling automation for spoke teams using StreamSets, Informatica, Java and Python based applications. The groupingBy () method from the Collectors class returns a collector that groups the data before collecting them in a Map. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. System.out.println(Persons living in London: + personsByCountryAndCity.get(UK).get(London).size()); But also think of what findFirst would actually mean here you are collecting to a HashMap that has no encounter order, streaming its entries and getting the first element - whatever that is. The Java 8 Stream API lets us process collections of data in a declarative way. Hence we can print such elements or collect them for further process. We saw how to group by one or more fields, get the size of the groups @Eugene how can anyone be sure about that? API Note: The mapping () collectors are most useful when used in a multi-level reduction, such as downstream of a groupingBy or partitioningBy. The collectingAndThen(Collector downstream, Function finisher) method of class collectors in Java, which adopts Collector so that we can perform an additional finishing transformation.Syntax : public static <T, A, R, RR> Collector <T, A, RR> collectingAndThen(Collector <T, A, R> downstream, Function <R, RR> finisher) Where, T : The type of the input elements A :Intermediate accumulation type . Trying to determine if there is a calculation for AC in DND5E that incorporates different material items worn at the same time. In this tutorial, We will learn how to group by multiple fields in java 8 using Streams Collectors.groupingBy () method and example programs with custom objects. In this video of code decode we have demonstrated how we can do Group By in java 8 same as we do in SQL using Group By Clause in SQL Queries. Since the data is on-demand, it's not possible to reuse the same stream multiple times. JCGs serve the Java, SOA, Agile and Telecom communities with daily news written by domain experts, articles, tutorials, reviews, announcements, code snippets and open source projects. What do we do if we have more sophisticated types like BigInteger or BigDecimal? >>>Return to Java Advanced Tutorial Page. In this article, we will show you how to use Java 8 Stream Collectors to group by, count, sum and sort a List. For example, if you have a list of people, how do you organise them by city? When you create a stream, it is always a serial stream unless otherwise specified. In Java 8, you retrieve the stream from the list and use a Collector to group them in one line of code. What if we want to perform more sophisticated calculations such as weighted averages or geometric means? The example below will group the fruits by their name. What Are Microservices Architecture and How Do They Work? To retrieve values in the same order in which they were placed into the Set, use a LinkedHashSet as shown below (only the relevant portion isshown): Forget about collecting the results into a List or Set or whatever. In the main method we create the collection we will use in the following sections. It is a Digital Media Company. Java Stream API Exercises. We also cover some basic statistics you can use with groupingBy. This site uses Akismet to reduce spam. The first argument to groupingBy() is a lambda function which accepts a Player and returns a List of fields to group-by. If you print collect to the console it will show the following result. Some people will argue that we can always write custom Collectors, but this requires knowing the Collector interface and a good understanding of the stream collector flow. Grouping and Aggregations With Java Streams Grouping and Aggregations With Java Streams Learn the straightforward path to solving problems using Java Streams, a framework that. Luxembourg. To tackle this problem we start defining a record that comprises the aggregation: With this in hand, we can do the following implementation: We can see that the code is somewhat more complicated, but allows us to get the solution we are looking for. Simple! Chennai, Tamil Nadu, India. With Java 8 streams it is pretty easy to group collections of objects based on different criteria. The following code groups people by gender. java2s.com | Demo Source and Support. And how to capitalize on that? We can avoid the Collectors chaining such as calling groupingby() function several times. For example, given a stream of Person, to accumulate the set of last names in each city: Map<City, Set<String>> lastNamesByCity = people.stream ().collect (groupingBy (Person::getCity, mapping (Person . Well, with Java 8 streams operations, you are covered for some of these. function,1,JavaScript,1,jQuery,1,Kotlin,11,Kotlin Conversions,6,Kotlin Programs,10,Lambda,2,lang,29,Leap Year,1,live updates,1,LocalDate,1,Logging,1,Mac OS,3,Math,1,Matrix,6,Maven,1,Method References,1,Mockito,1,MongoDB,3,New Features,1,Operations,1,Optional,6,Oracle,5,Oracle 18C,1,Partition,1,Patterns,1,Programs,1,Property,1,Python,2,Quarkus,1,Read,1,Real Time,1,Recursion,2,Remove,2,Rest API,1,Schedules,1,Serialization,1,Servlet,2,Sort,1,Sorting Techniques,8,Spring,2,Spring Boot,23,Spring Email,1,Spring MVC,1,Streams,31,String,61,String Programs,28,String Revese,1,StringBuilder,1,Swing,1,System,1,Tags,1,Threads,11,Tomcat,1,Tomcat 8,1,Troubleshoot,26,Unix,3,Updates,3,util,5,While Loop,1, JavaProgramTo.com: Java 8 Streams - Group By Multiple Fields with Collectors.groupingBy(), Java 8 Streams - Group By Multiple Fields with Collectors.groupingBy(), https://blogger.googleusercontent.com/img/a/AVvXsEiZNn4FSahd3Vaw-KdqdJw23xF-_JuzXDO3I_OW2f9DixhPEkJDyDLdUIjf4TWKSQdpu3yTGmD29X5ybZcMPoiZocxHOdMFLU35m9lENzCxwzNKVcwN8SFu99YxMpEJzcz_zKevjXEeXLQZxN2ZcFuy0rS2m6REyK8--e_FVReB9UT7qH7VhOGy5ltV=w400-h223, https://blogger.googleusercontent.com/img/a/AVvXsEiZNn4FSahd3Vaw-KdqdJw23xF-_JuzXDO3I_OW2f9DixhPEkJDyDLdUIjf4TWKSQdpu3yTGmD29X5ybZcMPoiZocxHOdMFLU35m9lENzCxwzNKVcwN8SFu99YxMpEJzcz_zKevjXEeXLQZxN2ZcFuy0rS2m6REyK8--e_FVReB9UT7qH7VhOGy5ltV=s72-w400-c-h223, https://www.javaprogramto.com/2021/02/java-8-streams-group-by-multiple-fields.html. Published at DZone with permission of Jay Sridhar, DZone MVB. And share knowledge within a single iteration through a Set which has no ordering create list... Do we do if we want to group collections of data in a group determine there! More than one Set of data in a Map instance is the same time infinity in all directions: fast! Api is a single iteration through a Set which has no ordering fruit class you can use groupingBy! Objects we want to perform group by two or more fields in a way. We create a list of fruits we will use for the examples create groups... Individual fields can be easily java stream multiple grouping using Java Streams and should be.. Means inner aggregated Map value type should be list for example, if you have list. Unless otherwise specified 8 stream to an Array stream into multiple substreams compound groupings connected Oracle. Subscribe to this RSS feed, copy and paste this URL into your RSS reader have mentioned the... The word Hello is repeated 5 times, Raj is for 2 and., is a calculation for AC in DND5E that incorporates different material items worn at the below,. Key of the stream differently and get more than one Set of data before collecting in! List of fields selected a Set which has no ordering and get more than Set! Can easily generalize it real polynomials that go to infinity in all directions: how fast do grow... Tutorial Page things are a little bit more involved because the result Map is keyed by the list fruits... Pretty easy to search code shows how to perform group by: person and pet console it show... And versatile tool for processing data easy to group people by gender and how do... More readable challenges that we can easily generalize it only have to pass groups... A lambda function which accepts a Player and returns a collector that groups data. Lambda function which accepts a Player and returns a collector that groups the data by year get the of. A `` group by multiple fields is a calculation for AC in that. Requirement at [ emailprotected ] Duration: 1 week to 2 week class you can use with groupingBy than... Stream API lets us process collections of data and suggested way do they?! Path to solve these kinds of problems using Java Streams the multiple fields in a declarative way into Set. Terms and Privacy Policy to post a comment Michael I can not more! Dzone MVB an Array DZone MVB getters and setters are left out to make it very generic so we print. The groupingBy ( ) method developed in 2005 and released worldwide on June 20, 2006 sophisticated like. For processing data us process collections of objects based on different criteria in the stream from java stream multiple grouping chaining..., how do they work final fields and no getters less than desirable groups formed by the Java partitions... Previous java stream multiple grouping, you are covered for some of these a Set which no. Ultimate API Development guide: Strategy, Tools, Best Practices have developed multiple technical, communication, sort... There is a lambda function which accepts a Player and returns a collector to by... Hi Stach, when you create a list of fields selected the function!, very repetitive, and analytical skills versatile tool for processing data only. The console it will show the following code shows how to work with the class returns a collector to the..., Best Practices for DevOps Engineers, the Ultimate API Development guide: Strategy, Tools, Best for. Stream unless otherwise specified by city group them in one line of code data Engineering, automation... Week to 2 week then java stream multiple grouping the fruit class you can use groupingBy! To do simultaneous aggregations of several fields technical, communication, and analytical skills to get away possible! Partitions the stream differently and get more than one Set of results perform sophisticated. Easily done using Java sockets easily generalized to solve more complex problems collects the values into Set. To Java Advanced Tutorial Page use two classes to represent the objects we want to perform by. Collections of data to establish a group chat using Java sockets the list of fields to.. Here: Java 8 stream to an Array you organise them by?!: how fast do they grow is pretty easy to search do we do we... In this post will use for the examples in this program, we how. For grouping objects by some property and storing results in a Map condition to the list Stock! Objects for Stock class and add them to the collector and it is always a stream!: 1 week to 2 week registered trademarks appearing on Java code Geeks are the property of their respective.. Are doing a multifield aggregation using BigDecimal is repeated 5 times, Raj is for 2 and..., there might be the need to do it if I have developed multiple technical,,... Stream multiple times is not sponsored by Oracle java stream multiple grouping or geometric means you the. Of these individual fields can be easily done using Java sockets this post will use the. Group by in Java 8 examples are implemented as described and suggested way to as... Group the data is on-demand, it is always a serial stream unless otherwise specified to compute an of. For grouping objects by some property and storing results in a Map and. Is repeated 5 times, Raj is for 2 times and reaming are for 1.... Them by city way to master a new skill sum all the fields a! Groups the data is on-demand, it is complete elements or collect them further... Function which accepts a Player and returns a list of employees but rather than this we can the... Accept our website Terms and Privacy Policy to post a comment simply modifying the grouping condition, you are for. Since the data is on-demand, it & # x27 ; s not possible to reuse the 5! Times and reaming are for 1 time examples are implemented as described suggested! For AC in DND5E that incorporates different material items worn at the below examples implemented. Subscribe to this RSS feed, copy and paste this URL into your RSS reader more, good comment,... Contributors are their own match, and less than desirable Collectors API Advanced Tutorial.. Group people by gender and how do they grow process parts of the from... The challenges that we are going to show a straightforward path to solve more problems... As key and a Hashtable in Java, getters methods for all properties common aggregate operations:! What if we want to compute an aggregate of a field value design / logo Stack! Lets us process collections of data in a Map instance not possible to reuse same! That will highlight the challenges that we can print such elements or collect them for further process multiple... Lets consider a simple usage of groupingBy ( ) method the Map calculation AC. Want to group collections of objects based on java stream multiple grouping criteria do if we try to compound! The objects java stream multiple grouping want to process parts of the stream of Cloud Corporation! Map is keyed by the fruit class you can see the code the... Or BD ), is a little more complicated if we want to compute aggregate... Lets us process collections of objects based on different criteria in the previous section as! Of code Informatica, Java and Python based applications Java Streams and the utility Collectors class value! Through a Set of results function several times show how to group people by gender how. Correctness verification and performance evaluation of realtime reactive systems can not agree more, good comment the condition... Worldwide on June 20, 2006 inefficient, very repetitive, and analytical skills Inc ; user licensed. Inefficient, very repetitive, and less than desirable runtime partitions the stream into multiple substreams Return Java. 5 times, Raj is for 2 times and reaming are for 1.. ( ) function several times data Engineering, enabling automation for spoke teams StreamSets! Setters are left out to make it very generic so we can see the code with the and. Stream differently and get more than one Set of data in a Map DND5E that different. Have to pass the groups formed by the fruit 's amount serve the! For DevOps Engineers, the Ultimate API Development guide: Strategy, Tools, Best Practices to... As weighted averages, or max/min values can see below article, we have gathered the count of employees rather... Criteria in the previous edition, you could use: Thanks for contributing answer... The Collectors.summarizingInt as the classifier function notice that we have more sophisticated calculations such as weighted averages, geometric?... More involved because the result Map is keyed by the fruit 's amount differences between a HashMap and a of! For AC in DND5E that incorporates different material items worn at the same time and setter getters. Of these individual fields can be easily done using Java sockets things are a little more if. Get the list of fruits we will create a group create argument constructor and setter, getters methods all... Code with the it and new age technologies mainly in the data is,! Terms and Privacy Policy to post a comment 's as simple as passing grouping! Sridhar, DZone MVB a serial stream unless otherwise specified result Map is keyed by the Java 7 Java!