POJO stands for “Plain Old Java Object” — it’s a pure data structure that has fields with getters and possibly setters, and may override some methods from Object (e.g. equals) or some other interface like Serializable, but does not have behavior of its own.
Normal Class: A Java classJava Beans:
Autoboxing and unboxing are introduced in Java 1.5 to automatically convert the primitive type into boxed primitive( Object or Wrapper class). autoboxing allows you to use primitive and object type interchangeably in Java in many places like an assignment, method invocation etc. If you have been using Collections like HashMap or ArrayList before Java
| Early | Late |
| Compile time | Run time |
| Overloading | Overriding |
To get jsp response as a string inside servlet is possible by wrapping the HttpServletResponse and overriding getWriter methods.
Servlet
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public class TestServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpServletResponseWrapper responseWrapper = new HttpServletResponseWrapper(response) { private final StringWriter sw = new StringWriter(); @Override public PrintWriter getWriter() throws IOException { return new PrintWriter(sw); } @Override public String toString() { return sw.toString(); } }; request.getRequestDispatcher("test.jsp").include(request, responseWrapper); String content = responseWrapper.toString(); System.out.println("Output : " + content); response.getWriter().write(content); } } |
JSP
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<%@page contentType="text/html" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Hello world</title> </head> <body> <h1><%= "Hello world from a JSP!" %></h1> </body> </html> |
The below example shows Java program to sort a Map by values in ascending and descending order, you can see that it’s so easy to sort the Map.
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public static void main(String args[]) { Map < String, Integer > map = new HashMap < String, Integer > (); map.put("A", 34); map.put("B", 25); map.put("C", 50); map.put("D", 50); // "duplicate" value System.out.println(entriesSortedByValues(map)); } static < K, V extends Comparable < ? super V >> List < Entry < K, V >> entriesSortedByValues(Map < K, V > map) { List < Entry < K, V >> sortedEntries = new ArrayList < Entry < K, V >> (map.entrySet()); Collections.sort(sortedEntries, new Comparator < Entry < K, V >> () { @Override public int compare(Entry < K, V > e1, Entry < K, V > e2) { //return e1.getValue().compareTo(e2.getValue()); // if ascending order return e2.getValue().compareTo(e1.getValue()); // if descending order } }); return sortedEntries; } |
collection : A collection(with small ‘c’) represents a group of objects/elements.
Collection : The root interface of Java Collections Framework.
Collections : A utility class that is a member of the Java Collections Framework.
The String is one of the most important classes in Java and anyone who starts with Java programming uses String to print something on the console by using famous System.out.println() statements. Many Java beginners not aware that String is immutable and final in Java and every modification in String creates a new String object.
In Java, there are three different ways for reading input from the user in the command line (console).
1.Using Buffered Reader Class
This method is used by wrapping the System.in (standard input stream) in an InputStreamReader which is wrapped in a BufferedReader, we can read input from the user in the command
Given a string, bellow it shows the boolean condition to find Lowercase characters, Uppercase characters.
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String password = "Password"; boolean hasUppercase = !password.equals(password.toLowerCase()); boolean hasLowercase = !password.equals(password.toUpperCase()); |