Java hashmap keys to string

Преобразование карты в строку в Java

Узнайте, как преобразовать карту в строку и наоборот, используя как основные методы Java, так и сторонние библиотеки.

1. Обзор

В этом уроке мы сосредоточимся на преобразовании из Map в String и наоборот.

Во-первых, мы посмотрим, как достичь этого с помощью основных методов Java, а затем мы будем использовать некоторые сторонние библиотеки.

2. Пример базовой карты

Во всех примерах мы будем использовать одну и ту же реализацию Map :

Map wordsByKey = new HashMap<>(); wordsByKey.put(1, "one"); wordsByKey.put(2, "two"); wordsByKey.put(3, "three"); wordsByKey.put(4, "four");

3. Преобразуйте карту в строку путем итерации

Давайте переберем все ключи в нашей карте и для каждого из них добавим комбинацию ключ-значение к нашему результирующему объекту StringBuilder |.

Для целей форматирования мы можем заключить результат в фигурные скобки:

public String convertWithIteration(Map map) < StringBuilder mapAsString = new StringBuilder("<"); for (Integer key : map.keySet()) < mapAsString.append(key + "=" + map.get(key) + ", "); >mapAsString.delete(mapAsString.length()-2, mapAsString.length()).append(">"); return mapAsString.toString(); >

Чтобы проверить, правильно ли мы преобразовали нашу карту , давайте проведем следующий тест:

@Test public void givenMap_WhenUsingIteration_ThenResultingStringIsCorrect() < String mapAsString = MapToString.convertWithIteration(wordsByKey); Assert.assertEquals("", mapAsString); >

4. Преобразуйте карту в строку с помощью потоков Java

Чтобы выполнить преобразование с помощью потоков, нам сначала нужно создать поток из доступных ключей Map .

Во-вторых, мы сопоставляем каждый ключ с читаемой человеком строкой .

Наконец, мы объединяем эти значения и для удобства добавляем некоторые правила форматирования с помощью метода Collectors.joining() :

public String convertWithStream(Map map) < String mapAsString = map.keySet().stream() .map(key ->key + "=" + map.get(key)) .collect(Collectors.joining(", ", "")); return mapAsString; >

5. Преобразуйте карту в строку с помощью Guava

Давайте добавим Guava в наш проект и посмотрим, как мы можем добиться преобразования в одной строке кода:

 com.google.guava guava 27.0.1-jre 

Чтобы выполнить преобразование с помощью класса Joiner Guava, нам нужно определить разделитель между различными записями Map и разделитель между ключами и значениями:

public String convertWithGuava(Map map) < return Joiner.on(",").withKeyValueSeparator(" https://search.maven.org/search?q=a:commons-collections4%20AND%20g:org.apache.commons" rel="noopener noreferrer" target="_blank">Apache Commons , давайте сначала добавим следующую зависимость:
 
"> org.apache.commons commons-collections4 4.2 
 
Соединение очень простое – нам просто нужно вызвать StringUtils.метод join :
 
public String convertWithApache(Map map)
 
Одно особое упоминание относится к методу debug Print , доступному в Apache Commons. Это очень полезно для целей отладки.
 
MapUtils.debugPrint(System.out, "Map as String", wordsByKey);
 
Отладочный текст будет записан на консоль:
 
Map as String = < 1 = one java.lang.String 2 = two java.lang.String 3 = three java.lang.String 4 = four java.lang.String >java.util.HashMap
 
7. Преобразуйте строку в карту с помощью потоков
 
Чтобы выполнить преобразование из String в Map , давайте определим, где нужно разделить и как извлечь ключи и значения:
 
public Map convertWithStream(String mapAsString) < Mapmap = Arrays.stream(mapAsString.split(",")) .map(entry -> entry.split(" wp-block-codemirror-blocks-code-block code-block">
">public Map convertWithGuava(String mapAsString)
 
9. Заключение
 
В этом уроке мы рассмотрели, как преобразовать Map в String и наоборот, используя как основные методы Java, так и сторонние библиотеки.
 
Реализацию всех этих примеров можно найти на GitHub .
 
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Источник
 
Map to String Conversion in Java
 
 
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1. Overview
 
In this tutorial, we'll focus on conversion from a Map to a String and the other way around.
 
First, we'll see how to achieve these using core Java methods, and afterward, we'll use some third-party libraries.
 
2. Basic Map Example
 
In all examples, we're going to use the same Map implementation:
 
Map wordsByKey = new HashMap<>(); wordsByKey.put(1, "one"); wordsByKey.put(2, "two"); wordsByKey.put(3, "three"); wordsByKey.put(4, "four");
 
3. Convert a Map to a String by Iterating
 
Let's iterate over all the keys in our Map and, for each of them, append the key-value combination to our resulting StringBuilder object.
 
For formatting purposes, we can wrap the result in curly brackets:
 
public String convertWithIteration(Map map) < StringBuilder mapAsString = new StringBuilder("<"); for (Integer key : map.keySet()) < mapAsString.append(key + "=" + map.get(key) + ", "); >mapAsString.delete(mapAsString.length()-2, mapAsString.length()).append(">"); return mapAsString.toString(); >
 
To check if we converted our Map correctly, let's run the following test:
 
@Test public void givenMap_WhenUsingIteration_ThenResultingStringIsCorrect() < String mapAsString = MapToString.convertWithIteration(wordsByKey); Assert.assertEquals("", mapAsString); >
 
4. Convert a Map to a String Using Java Streams
 
To perform conversion using streams, we first need to create a stream out of the available Map keys.
 
Second, we're mapping each key to a human-readable String.
 
Finally, we're joining those values, and, for the sake of convenience, we're adding some formatting rules using the Collectors.joining() method:
 
public String convertWithStream(Map map) < String mapAsString = map.keySet().stream() .map(key ->key + "=" + map.get(key)) .collect(Collectors.joining(", ", "")); return mapAsString; >
 
5. Convert a Map to a String Using Guava
 
Let's add Guava into our project and see how we can achieve the conversion in a single line of code:
 
 com.google.guava guava 31.0.1-jre 
 
To perform the conversion using Guava's Joiner class, we need to define a separator between different Map entries and a separator between keys and values:
 
public String convertWithGuava(Map map)
 
6. Convert a Map to a String Using Apache Commons
 
To use Apache Commons, let's add the following dependency first:
 
 org.apache.commons commons-collections4 4.2 
 
The joining is very straightforward — we just need to call the StringUtils.join method:
 
public String convertWithApache(Map map)
 
One special mention goes to the debugPrint method available in Apache Commons. It is very useful for debugging purposes.
 
MapUtils.debugPrint(System.out, "Map as String", wordsByKey);
 
the debug text will be written to the console:
 
Map as String = < 1 = one java.lang.String 2 = two java.lang.String 3 = three java.lang.String 4 = four java.lang.String >java.util.HashMap
 
7. Convert a String to a Map Using Streams
 
To perform conversion from a String to a Map, let's define where to split on and how to extract keys and values:
 
public Map convertWithStream(String mapAsString) < Mapmap = Arrays.stream(mapAsString.split(",")) .map(entry -> entry.split("=")) .collect(Collectors.toMap(entry -> entry[0], entry -> entry[1])); return map; >
 
8. Convert a String to a Map Using Guava
 
A more compact version of the above is to rely on Guava to do the splitting and conversion for us in a one-line process:
 
public Map convertWithGuava(String mapAsString)
 
9. Conclusion
 
In this article, we saw how to convert a Map to a String and the other way around using both core Java methods and third-party libraries.
 
The implementation of all of these examples can be found over on GitHub.
 
 
 
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
 
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
 
Critically, it has very minimal impact on your server's performance, with most of the profiling work done separately - so it needs no server changes, agents or separate services.
 
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you'll have results within minutes:
 
Источник
 
Java HashMap toString()
 
Introduction
 
Returns a string representation of this map. The string representation consists of a list of key-value mappings in the order returned by the map's entrySet view's iterator, enclosed in braces ("<">). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign (" --" + UIN; > @Override public boolean equals(Object otherStudent) < boolean result = false; if (otherStudent instanceof Student) < Student otherStudent1 = (Student) otherStudent; result = ( this .name.equalsIgnoreCase(otherStudent1.name) && this .UIN == otherStudent1.UIN); >return result; > @Override public int hashCode() < int hash = 7; hash = 79 * hash + Objects.hashCode( this .name); hash = 79 * hash + this .UIN; return hash; > > class DemoStudent < public static void main(String[] args) < HashMapInteger, Student> hm = new HashMap<>(); Student s1 = new Student( "Pranay" , 10001); Student s2 = new Student( "Pranay" , 10001); hm.put(1, s1); hm.put(2, s2); hm.remove(1); System.out.println(hm.toString()); System.out.println(s1.equals(s2)); > >
 
import javax.servlet.http.*; import javax.servlet.*; import java.util.ArrayList; import java.util.HashMap; import chess.modele.Usager; public class Unlog extends HttpServlet < public void doPost(HttpServletRequest request, HttpServletResponse reponse) throws ServletException, java.io.IOException < processRequest(request, reponse); >// w w w .d em o 2 s . c om public void doGet(HttpServletRequest request, HttpServletResponse reponse) throws ServletException, java.io.IOException < processRequest(request, reponse); >public void processRequest(HttpServletRequest request, HttpServletResponse reponse) < reponse.setContentType("text/html"); try < getServletContext().log("INVALIDATE"); getServletContext().log("invalidate: " + request.getSession().getAttribute("usr_id")); HashMapString, Usager> connectes = (HashMapString, Usager>) request.getSession().getServletContext() .getAttribute("connectes"); String usr_id = (request.getSession().getAttribute("usr_id") == null) ? "" : request.getSession().getAttribute("usr_id").toString(); // String usr_id = "xkcd"; connectes.remove(usr_id); getServletContext().log("CONNECTES: " + connectes.toString()); ; request.getSession().invalidate(); > catch (Exception e) < getServletContext().log("exception dans SetUsrId: " + e.getMessage()); > > >
 
import java.util.HashMap; import java.util.List; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import br.com.lvc.utility.screen.BaseActivity; public class MainActivityDois extends BaseActivity < @Override/* w w w .d e m o 2 s . c o m */ protected void onCreate(Bundle savedInstanceState) < super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Button button = (Button) findViewById(R.id.button); button.setText("TELA DOIS"); > public void onClickTesteDataBase(View view) < try < HashMapString, String> value = new HashMapString, String>(); value.put("KEY UM", "VALUE UM"); value.put("KEY DOIS", "VALUE 2"); value.put("KEY TRES", "VALUE 3"); value.put("KEY QUATRO", "VALUE 4"); Pessoa pessoa = new Pessoa("leo", value); PessoaDAO pessoaDAO = PessoaDAO.getInstance(this); pessoaDAO.save(pessoa); Log.i("COUNT", "COUNT: " + pessoaDAO.count()); List pessoas = pessoaDAO.getAllElements(); for (Pessoa pessoa2 : pessoas) < HashMapString, String> value2 = pessoa2.getHashMapUm(); Log.i("HASH", "HASH DESSERIALIZE: " + value2.toString()); > > catch (Exception e) < e.printStackTrace(); >> >
 
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