I am using linux(mint mate), and installed maven by download & unzip & config the environment, I could use the mvn command. I want to have man mvn, not just mvn -help, any tip? @Update: To make the question clear, there is no man page for mvn, because I install maven by unzip, so I want to install man…
Tag: java
How to map an immutable collection with JPA and Hibernate
I am using JPA 2.1 and Hibernate as a JPA implementation, and I want to load a relationship as an immutable collection. Let’s take an example of an Employer parent entity that has an employees child collection. What can be done to instruct JPA to load an immutable employees collection? Answer You can us…
org.postgresql.util.PSQLException: ERROR: relation “app_user” does not exist
I have an application that I’m using spring boot and postgres. I’m getting this error when I try to create a user. When I run this query on my database, I get the same error: But if I change that to: It works. How can I configure that on my spring boot app? dependencies in pom.xml: application.pro…
Not supported for DML operations with JPA update query
This has been asked once before but the solution did not solve the issue. I am creating a JUnit test: The query the above test is calling is: Error: Answer The @Modifying annotation must be placed on the updateMaterialInventory method, along to the @Query annotation, to let Spring-data know that the query is …
Are non-capturing groups redundant?
Are optional non-capturing groups redundant? Is the following regex: semantically equivalent to the following regex? Answer Your (?:wo)?men and (wo)?men are semantically equivalent, but technically are different, namely, the first is using a non-capturing and the other a capturing group. Thus, the question is…
Is the String args[] parameter needed for programs that do not require command line arguments?
As far as I know, String args[] accepts an array of elements of type String – a mechanism through which the runtime system passes information to an application. If we take a simple addition program like this: It is obvious that the program does not need any command line arguments to calculate the result…
How to send and receive a DSA public/private signed message in Java
I cannot find any good (complete) documentation on how to exchange a public/private key signed message in Java. I have yet to find a concise document on the minimum steps needed to generate a public key and private key using DSA, sign a byte[], and verify it. The documentation from Oracle is too broken up and…
Convert a for loop to concat String into a lambda expression
I have the following for loop which iterates through a list of strings and stores the first character of each word in a StringBuilder. I would like to know how can I transform this to a lambda expression Answer Assuming you call toString() on the StringBuilder afterwards, I think you’re just looking for…
Declare an array in java without size
Hello am trying to declare an array in java but i do not want the array to have a specific size because each time the size must be different. I used this declaration: int[] myarray5; but when am trying the below code there is an error on myarray5 and also when am printing the array: Answer There is a NullPoin…
JSON Error “java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $”
This create Exception Big thanks for help. Answer Let’s look at the error you are receiving. Expected BEGIN_OBJECT Your JSON is an object, and all JSON objects are enclosed in curly braces ({}). BEGIN_OBJECT is therefore {. And it’s expecting it somewhere. but was STRING But instead he found a str…