mkyong In Java, we can get the keys and values via map.entrySet() Map<String, String> map = new HashMap<>(); // Get keys and values for (Map.Entry<String, String> entry : map.entrySet()) { String k = entry.getKey(); String v = entry.getValue(); System.out.println("Key: " + k + ", Value: " + v); } // Java 8 map.forEach((k, v) -> { …
Spring JdbcTemplate example to get a large ResultSet and process it. P.S Tested with Java 8 and Spring JDBC 5.1.4.RELEASE 1. Get large ResultSet 1.1 Below is a classic findAll to get all data from a table. BookRepository.java public List<Book> findAll() { return jdbcTemplate.query( "select * from books", (rs, rowNum) -> new Book( rs.getLong("id"), rs.getString("name"), …
Below example, the jdbcTemplate.queryForList returns an object of Integer and we try to convert it into a Long directly: public List<Customer> findAll() { String sql = "SELECT * FROM CUSTOMER"; List<Customer> customers = new ArrayList<>(); List<Map<String, Object>> rows = jdbcTemplate.queryForList(sql); for (Map row : rows) { Customer obj = new Customer(); obj.setID(((Long) row.get("ID"))); // the …
In Java, we can combine RandomAccessFile and FileChannel to lock a file before writing. LockFileAndWrite.java package com.mkyong; import java.io.File; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.channels.FileLock; import java.util.concurrent.TimeUnit; public class LockFileAndWrite { public static void main(String[] args) { writeFileWithLock(new File("D:\\server.log"), "mkyong"); } public static void writeFileWithLock(File file, String content) { // auto close and release the …
In Java, we can use the Apache Commons IO ReversedLinesFileReader to read the last few lines of a File. pom.xml <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>2.6</version> </dependency> 1. Test Data A server log file sample d:\\server.log a b c d 1 2 3 4 5 2. Read Last Line 2.1 Read the last 3 lines of a …
In this tutorial, we will show you how to use Spring Boot JDBC SimpleJdbcCall to call a stored procedure and stored function from a Oracle database. Technologies used : Spring Boot 2.1.2.RELEASE Spring JDBC 5.1.4.RELEASE Oracle database 19c HikariCP 3.2.0 Maven 3 Java 8 Unlike JdbcTemplate, Spring Boot didn’t create any SimpleJdbcCall automatically, we have …
In this tutorial, we will show you how to use Spring Boot JDBC JdbcTemplate and NamedParameterJdbcTemplate. Technologies used : Spring Boot 2.1.2.RELEASE Spring JDBC 5.1.4.RELEASE HikariCP 3.2.0 H2 in-memory database 1.4.197 Maven 3 Java 8 In Spring Boot JDBC, the database related beans like DataSource, JdbcTemplate and NamedParameterJdbcTemplate will be configured and created during the …
Java 8 stream and regular expression examples. Note Learn the basic regular expression at Wikipedia 1. String.matches(regex) 1.1 This example, check if the string is a number. JavaRegEx1.java package com.mkyong.regex; import java.util.Arrays; import java.util.List; public class JavaRegEx1 { public static void main(String[] args) { List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211"); for (String number …
As title, we can use flatMap to convert it. Java9Example1.java package com.mkyong.test; import java.util.Arrays; import java.util.List; import java.util.Scanner; import java.util.stream.Collectors; public class Java9Example1 { public static void main(String[] args) { List<String> numbers = Arrays.asList("1", "2", "A", "B", "C1D2E3"); List<List<String>> collect = numbers.stream() .map(x -> new Scanner(x).findAll("\\D+") .map(m -> m.group()) .collect(Collectors.toList()) ) .collect(Collectors.toList()); collect.forEach(x -> System.out.println(x)); …
Call the .values() method of the enum class to return an array, and loop it with the for loop: for (EnumClass obj : EnumClass.values()) { System.out.println(obj); } For Java 8, convert an enum into a stream and loop it: Stream.of(EnumClass.values()).forEach(System.out::println); 1. For Loop Enum 1.1 An enum to contain a list of the popular JVM …
Making a JDBC connection to the MySQL server with the latest mysql-connector-java:8.0.16 and hits the following SQLException: Tested with MySQL 5.7 Java 8 JDBC driver, mysql-connector-java 8.0.16 try (Connection conn = DriverManager.getConnection( "jdbc:mysql://127.0.0.1:3306/test", "root", "password")) { //… } catch (Exception e) { e.printStackTrace(); } Output java.sql.SQLException: The server time zone value ‘Malay Peninsula Standard Time’ …
In Java, we can use Long.valueOf() to convert an Integer to a Long TestInteger.java package com.mkyong.example; public class TestInteger { public static void main(String[] args) { Integer num = 1; System.out.println(num); // 1 Long numInLong = Long.valueOf(num); System.out.println(numInLong); // 1 } } References Long.valueOf JavaDocs)
Few Java 8 examples to execute streams in parallel. 1. BaseStream.parallel() A simple parallel example to print 1 to 10. ParallelExample1.java package com.mkyong.java8; import java.util.stream.IntStream; public class ParallelExample1 { public static void main(String[] args) { System.out.println("Normal…"); IntStream range = IntStream.rangeClosed(1, 10); range.forEach(System.out::println); System.out.println("Parallel…"); IntStream range2 = IntStream.rangeClosed(1, 10); range2.parallel().forEach(System.out::println); } } Output Normal… 1 2 …
The following Java examples will print a list of all the prime numbers up to 1,000: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 …
Ordinal binding or index binding: String name = stat.getString(2); BigDecimal salary = stat.getBigDecimal(3); Timestamp createdDate = stat.getTimestamp(4); Named binding: String name = stat.getString("NAME"); BigDecimal salary = stat.getBigDecimal("SALARY"); Timestamp createdDate = stat.getTimestamp("CREATED_DATE"); If we mixed both like this: String name = stat.getString(2); BigDecimal salary = stat.getBigDecimal("SALARY"); Timestamp createdDate = stat.getTimestamp(4); Error: java.sql.SQLException: operation not allowed: Ordinal …
Java example to convert java.time.ZonedDateTime to java.sql.Timestamp and vice verse. 1. ZonedDateTime -> Timestamp TimeExample1.java package com.mkyong.jdbc; import java.sql.Timestamp; import java.time.ZonedDateTime; public class TimeExample1 { public static void main(String[] args) { ZonedDateTime now = ZonedDateTime.now(); // 1. ZonedDateTime to TimeStamp Timestamp timestamp = Timestamp.valueOf(now.toLocalDateTime()); // 2. ZonedDateTime to TimeStamp , no different Timestamp timestamp2 = …
Python example to print the key value of a dictionary. stocks = { ‘IBM’: 146.48, ‘MSFT’: 44.11, ‘CSCO’: 25.54 } print(stocks) for k, v in stocks.items(): print(k, v) for k in stocks: print(k, stocks[k]) Output {‘IBM’: 146.48, ‘MSFT’: 44.11, ‘CSCO’: 25.54} IBM 146.48 MSFT 44.11 CSCO 25.54 IBM 146.48 MSFT 44.11 CSCO 25.54 References Python …
Many examples are using the .count() as the terminal operation for .peek(), for example: Java 8 List<String> l = Arrays.asList("A", "B", "C", "D"); long count = l.stream().peek(System.out::println).count(); System.out.println(count); // 4 Output – It’s working fine. A B C D 4 However, for Java 9 and above, the peek() may print nothing: Java 9 and above …
In Java, we can use Timestamp.valueOf(LocalDateTime) to convert a LocalDateTime into a Timestamp. 1. LocalDateTime Timestamp Java example to convert java.time.LocalDateTime to java.sql.Timestamp and vice verse. TimeExample.java package com.mkyong; import java.sql.Timestamp; import java.time.LocalDateTime; public class TimeExample { public static void main(String[] args) { // LocalDateTime to Timestamp LocalDateTime now = LocalDateTime.now(); Timestamp timestamp = Timestamp.valueOf(now); …
Some Java Conferences and Events 2019. 1. JAX London (October 7–10, 2019) JAX London is a four-day conference for cutting edge software engineers and enterprise-level professionals. JAX brings together the world’s leading innovators in the fields of JAVA, microservices, continuous delivery and DevOps. Date: October 7–10, 2019 Location: Business Design Centre, London Discount(15%): mky_jxl19#15 Twitter: …
This is caused by the requested SID doesn’t exist in {ORACLE_HOME}/network/admin/tnsnames.ora P.S Tested with Oracle database 19c with ojdbc8.jar 1. JDBC try (Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:xe", "system", "password")) { //… } catch (SQLException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } Output: SQL State: 66000 Listener refused the connection with the following …
To uninstall Oracle database on Windows, we have to delete the all the related Ora* registry keys, files and folders manually. P.S Tested with Oracle database 19c on Windows 10 Note I can’t find any uninstaller to uninstall the Oracle database automatically? 1. Stop Oracle* services Press Windows key, type services, stop all Oracle related …
A JDBC CallableStatement example to show you how to call a stored function from PostgreSQL database. P.S Tested with PostgreSQL 11 and Java 8 pom.xml <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> 1. Call Function 1.1 Create a stored function and calling it via JDBC. FunctionReturnString.java package com.mkyong.jdbc.callablestatement; import java.sql.*; public class FunctionReturnString { public static void …
Since Java 1.6, JDBC 4.0 API, it provides a new feature to discover java.sql.Driver automatically, it means the Class.forName is no longer required. Just put any JDBC 4.x driver in the project classpath, and Java is able to detect it. For example, JDBC driver for PostgreSQL: pom.xml <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> And it works: …
A JDBC example to connect to a PostgreSQL, and print out all the tables from the default database postgres pom.xml <dependencies> <dependency> <groupId>org.postgresql</groupId> <artifactId>postgresql</artifactId> <version>42.2.5</version> </dependency> </dependencies> P.S Tested with Java 8 and postgresql jdbc driver 42.2.5 PrintAllTables.java package com.mkyong.jdbc; import java.sql.*; public class PrintAllTables { public static void main(String[] argv) { System.out.println("PostgreSQL JDBC Connection …
If Java 8, DateTimeFormatter, else SimpleDateFormat to change the date format in a String. 1. DateTimeFormatter (Java 8) Convert the String to LocalDateTime and change the date format with DateTimeFormatter DateFormatExample1.java package com.mkyong; import java.time.LocalDateTime; import java.time.format.DateTimeFormatter; public class DateFormatExample1 { // date format 1 private static final DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.S"); // date …
Different operating system has a different new line or line separator string: UNIX, Linux or Mac OSX = \n Windows = \r\n NewLineExample.java package com.mkyong; public class NewLineExample { public static void main(String[] args) { String original = "Hello World Java"; System.out.println(original); // add new line String originalNewLine = "Hello\nWorld\nJava"; System.out.println(originalNewLine); } } Output Hello …
Only Streams whose source are an IO channel like Files.lines(Path, Charset) need to be closed. Read this Stream JavaDocs Streams have a BaseStream.close() method and implement AutoCloseable, but nearly all stream instances do not actually need to be closed after use. Generally, only streams whose source is an IO channel (such as those returned by …
In Java, -Xms set initial Java heap size, while -Xmx set the maximum Java heap size. 1. Some java -Xms -Xmx examples : # Start with 128MB of memory, and allow the Java process to use up to 1024MB of memory. java -Xms128m -Xmx1024m # Start with 256MB of memory, and allow the Java process …
In Java, we have many ways to convert a File to a String. A text file for testing later. c:\\projects\\app.log A B C D E 1. Java 11 – Files.readString A new method Files.readString is added in java.nio.file.Files, it makes reading a string from File much easier. FileToString1.java package com.mkyong; import java.io.IOException; import java.nio.file.Files; import …
In Java, there are many ways to write a String to a File. 1. Java 11 – Files.writeString Finally, a new method added in java.nio to save a String into a File easily. StringToFileJava11.java package com.mkyong; import java.io.IOException; import java.nio.charset.StandardCharsets; import java.nio.file.Files; import java.nio.file.Paths; import java.nio.file.StandardOpenOption; public class StringToFileJava11 { public static void main(String[] args) …
FastJson provides easily APIs to convert Java objects to / from JSON JSON.toJSONString – Java objects to JSON JSON.parseObject – JSON to Java objects JSON.parseArray – JSON array to List of Java objects Note You may have interest to read this How to parse JSON with Jackson Overall, the FastJson is really simple and easy …
Here’s the Java password generator to generate a secure password that consists of two lowercase chars, two uppercase chars, two digits, two special chars, and pad the rest with random chars until it reaches the length of 20 characters. Secure password requirements: Password must contain at least two digits [0-9]. Password must contain at least …
Few Java examples to show you how to generate a random alphanumeric String, with a fixed length. 1. Random [a-ZA-Z0-9] 1.1 Generate a random alphanumeric String [a-ZA-Z0-9], with a length of 8. RandomExample.java package com.mkyong; import java.security.SecureRandom; public class RandomExample { private static final String CHAR_LOWER = "abcdefghijklmnopqrstuvwxyz"; private static final String CHAR_UPPER = CHAR_LOWER.toUpperCase(); …
In Java, we can use Double.parseDouble() to convert a String to double 1. Double.parseDouble() Example to convert a String 3.142 to an primitive double. String str = "3.142"; double pi = Double.parseDouble(str); System.out.println(pi); Output 3.142 2. Double.valueOf() Example to convert a String 3.142 to an Double object. String str = "3.142"; Double pi = Double.valueOf(str); …
In Java, we can use new ArrayList(Arrays.asList(array)) to convert an Array into an ArrayList ArrayExample1.java package com.mkyong; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class ArrayExample1 { public static void main(String[] args) { String[] str = {"A", "B", "C"}; List<String> list = new ArrayList<>(Arrays.asList(str)); list.add("D"); list.forEach(x -> System.out.println(x)); } } Output A B C D …
In this tutorial, we will show you how to parse JSON with JSON.simple Note You may have interest to read – How to parse JSON with Jackson or Gson JSON.simple short history This project was formerly JSON.simple 1.x from a Google code project by Yidong, now maintaining by Clifton Labs, read this JSON.simple history P.S …
Few Java examples to show you how to check if a String is numeric. 1. Character.isDigit() Convert a String into a char array and check it with Character.isDigit() NumericExample.java package com.mkyong; public class NumericExample { public static void main(String[] args) { System.out.println(isNumeric("")); // false System.out.println(isNumeric(" ")); // false System.out.println(isNumeric(null)); // false System.out.println(isNumeric("1,200")); // false System.out.println(isNumeric("1")); …
In Java, we can use (str != null && !str.isEmpty()) to make sure the String is not empty or null. StringNotEmpty.java package com.mkyong; public class StringNotEmpty { public static void main(String[] args) { System.out.println(notEmpty("")); // false System.out.println(notEmpty(null)); // false System.out.println(notEmpty("hello")); // true System.out.println(notEmpty(" ")); // true, a space… } private static boolean notEmpty(String str) { …
In Jackson, we can use the annotation @JsonView to control which fields of the same resource are displayed for different users. Table of contents: 1. Download Jackson 2. Define View Classes 3. Annotate model class with @JsonView 4. Testing the Jackson @JasonView 5. Download Source Code 6. References P.S Tested with Jackson 2.17.0 1. Download …