Next time you are asked to explain a design pattern in an interview, you could pick this as opposed to the very common factory and singleton design patterns. Q1. How will you go about using a builder design pattern instead of constructors to create thread-safe immutable objects? … Read more...
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Can you list 10 JEE best practices from your experience?
Core Java best practices and JEE best practices can reveal a lot about your experience as a Java developer.
Q1. Can you list 10 JEE best practices from your experience?
A1.
#1: Using datasources with JNDI lookups
DataSources make the code more portable than using the DriverManagers.
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Chrome Postman to test and debug RESTful Web Services
Step 1 You need to get the Postman extension for the Google chrome browser.
Step 2 Search and add POSTMAN.
Step 3 Once installed, open it from the Apps link.
Step 4 Set the TEST URL,
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Class invariant & designing by contract in Java
Q1. What is a class invariant? A1. Class invariant is — what must be true about each instance of a class? If an invariant fails then there could be a bug in either calling-method or called-method. It is convenient to put all the expressions required for checking invariants into reusable...
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Connecting DBeaver to Databases with Kerberos security & SSL
DBeaver is a universal tool to access any database or cloud application that has an ODBC or JDBC Driver such as MySQL, Oracle, Salesforce, Hive, Impala, Teradata, Redshift, Snowflake, etc. SQL Databases like Impala & Hive are secured with Kerberos & SSL. This post discusses how you can access an Impala or Hive database that is secured with Kerberos &
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Dealing with concurrent modifications in Java
There are scenarios where you need to deal with concurrent modifications in Java. Here are 2 scenarios that I can currently think of. Scenario 1: Looping through a list of items and removing an item in the list could lead to “ConcurrentModificationException“. … Read more ›...
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Debugging “NoSuchMethodError” in Java
The JAR hell issues also lead to exceptions like NoSuchMethodError or IllegalArgumentException. I have already discussed debugging JAR Hell issues. #1 Check the war file for any duplicate versions of the same jar The Maven’s transivie dependency might bring multiple versions of joda libraries like “ … Read more ›...
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Debugging connection refused issues in Java with 9 tips
Possible reasons for “refused connections” 1) Client & Server are not connected by the LAN. For example, they can be in the different zones. 2) The Server might not be running. 3) The server might be listening on a different port or the server might have not started properly as...
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Debugging JAR hell issues in Java
The following 3 questions are frequently asked by Java developers as an industrial strength Java project will have 100+ jar files. How often have you come across a Java application that requires different versions of the same library? How often do you see exceptions like NoSuchMethodError or IllegalArgumentException.
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Debugging Java version issues
1. Error: Unsupported major.minor version 51.0 error?
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2015-06-18 11:27:33,560 WARN [org.jboss.detailed.classloader.ClassLoaderManager] (main) Unexpected error during load of:org.apache.cxf.management.annotation.ManagedResource java.lang.UnsupportedClassVersionError: org/apache/cxf/management/annotation/ManagedResource : Unsupported major.minor version 51.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) at java.lang.ClassLoader.defineClass(ClassLoader.java:615) at org.jboss.classloader.spi.base.BaseClassLoader.access$200(BaseClassLoader.java:67) at org.jboss.classloader.spi.base.BaseClassLoader$2.run(BaseClassLoader.java:633) at org.jboss.classloader.spi.base.BaseClassLoader$2.run(BaseClassLoader.java:592) |
What does this error mean?
The above error means what version of the JRE that the class file is compatible with. “org/apache/cxf/management/annotation/ManagedResource” was compiled with based on the following
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J2SE 8 = 52, J2SE 7 = 51, J2SE 6.0 = 50, J2SE 5.0 = 49, JDK 1.4 = 48, |
So, “51” means it is compatible with “
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Debugging java.security.cert.CertificateException: Certificates do not conform to algorithm constraints
Why? You may have a certificate with SHA1RSA key size less than 1024 bits or you have a certificate in your chain that uses MD2RSA.
Explanation? MD2 was widely recognized as insecure and thus disabled in Java in version JDK 7 onwards.
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Debugging like a pro with eclipse IDE tutorial for Java developers
Often you get to work on a fully functional Java application that is already in production to fix production issues or to enhance its existing functionality. As a new Java developer in the team, it is not easy to get started and contributing. The approach would be slightly different from working on a brand new project.
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Debugging LinkageErrors in Java
What is a LinkageError in Java?
A jar that is being loaded by two different classloaders can throw a java.lang.LinkageError. For example, your application server (e.g JBoss) on startup loads that jar or has a directory with that jar. Also, your EAR or WAR you are deploying has that jar in its say WEB-INF/lib.
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