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Tag: java
Returning ResultSet without close?
I would like to have a database connection managing class which I can use for simple SQL commands like SELECT, INSERT etc. by simple calling something like this (class below): This is class I’ve found on web: Is this way of returning ResultSet without closing it (and closing the statement) right? How ca…
Java – Why can’t I use charAt() to see if a char equals another?
I want to see if a character in my string equals a certain other char value but I do not know what the char in the string is so I have used this: But I get the error: But “g” == “h” seems to work and I know you can use ‘==’ with char types. Is there another way to
What’s the difference between map() and flatMap() methods in Java 8?
In Java 8, what’s the difference between Stream.map() and Stream.flatMap() methods? Answer Both map and flatMap can be applied to a Stream<T> and they both return a Stream<R>. The difference is that the map operation produces one output value for each input value, whereas the flatMap operati…
How to check a Long for null in java
How do I check a Long value for null in Java? Will this work? Answer Primitive data types cannot be null. Only Object data types can be null. There are 8 primitive types in Java: Data Type Size Description byte 1 byte Int8 short 2 bytes Int16 int 4 bytes Int32 long 8 bytes Int64 float 4 bytes Single double
How to install Tomcat in Amazon Web Services EC2
I have created an instance in Amazon web services, and I have connected to the server using putty through ssh. But I do not know how to install tomcat 8 in amazon ec2. Please help me with this. Answer You can use yum tool to install the tomcat8 packer from amazon default repository. The command is: yum instal…
java.sql.SQLException: An attempt by a client to checkout a Connection has timed out
I have a java client server which is supposed to establish connection pool on startup but its failing on timeout error. There are so many threads on this same issue but none of the solutions worked for me AM using jdk 7 and below is the mchange maven dependency jdbc.properties Here is my DAO class which estab…
How to load JSON Schema file from java
My Project is a maven project and inside resources folder – src/main/resources folder I have a json schema file – “jsonschema.json ” package : src/main/resources file : jsonschema.json Now i want to validate my jsonobject with json schema How to load the schema.json file in to the code…
java.lang.IllegalStateException: Multiple representations of the same entity with @ManyToMany 3 entities
I have 3 entities with ManyToMany relationships: Role Entity: Permission Entity: Functionality Entity: I did the following: I have created 3 functionalities: Then created 2 permissions: Then created a role: I am getting the following exception: java.lang.IllegalStateException: Multiple representations of the …
Unable to create database using prepared statements in MySql
I am trying to create the database using a prepared statement in MySQL. Here I am passing the parameters as shown. But I am getting a syntax error. Is it possible to create tables and databases using prepared statements? Answer in a PreparedStatement can only be used to bind values (e.g., in where conditions …