How-to articles, tricks, and solutions about JAVA

To POST form data with the RestTemplate class in Spring, you can use the postForObject method and pass it a URL, an object containing the form data, and the response type.

To parse JSON in Kotlin, you can use the JSONObject class from the org.json package.

To sort a HashMap in Java, you can use the TreeMap class, which is a Map implementation that maintains its entries in ascending order, sorted according to the keys.

To hash a string using SHA-256 in Java, you can use the MessageDigest class from the java.security package.

To subtract a certain number of days from a Date object in Java, you can use the Calendar class.

If the Android SDK installation is unable to find the JDK (Java Development Kit), it could be because the JDK is not installed or is not installed in the default location.

In a JPA entity relationship, the CascadeType.ALL annotation specifies that all operations (persist, merge, remove, refresh, and detach) that are performed on the parent entity should be cascaded to the child entity.

If you are getting the "Could not create the Java virtual machine" error when trying to launch a Java program, it means that the Java Virtual Machine (JVM) is unable to allocate enough memory to run the program.

If code completion is not working in Eclipse, there are a few possible reasons:

To programmatically determine the operating system in Java, you can use the System.getProperty method and pass it the "os.name" property.

To create a new key-value pair in a Map in Java, you can use the put method.

The strings "%5B" and "%5D" are URL-encoded versions of the square brackets "[" and "]", respectively.

To execute a Java class from the command line, you will need to use the java command and specify the name of the class that you want to run.

To get the name of the currently executing method in Java, you can use the Thread.currentThread().getStackTrace() method.

There are a few possible reasons why Eclipse might not be able to find a Java Virtual Machine (JVM).

JavaServer Faces (JSF) is a user interface (UI) framework for building web applications.

In Java, the && and || operators are used in if statements to combine multiple conditions.

The "no main manifest attribute" error is usually caused by a missing or incorrect Main-Class attribute in the manifest file of a Java .jar file.

The java.lang.UnsupportedClassVersionError error is usually caused by trying to run a Java class that was compiled with a newer version of the Java compiler than the version of the JRE (Java Runtime Environment) that you are using.

To get a platform-dependent new line character in Java, you can use the System.lineSeparator() method.

A Maven snapshot is a version of a Maven artifact that is under active development and has not been released yet.

To convert a string in the format "2018-04-10T04:00:00.000Z" to a DateTime object in Java, you can use the org.joda.time.DateTime class and the DateTimeFormatter class.

If you are getting the error "The import javax.servlet can't be resolved", it means that the javax.servlet package is not available on the classpath.

To package/install a Maven project without running the tests, you can use the maven-install-plugin and specify the skipTests property as true.

To create a temporary directory/folder in Java, you can use the createTempDirectory() method of the Files class in the java.nio.file package.