For a long time, Java has provided built-in implementations of SAX and DOM, and no external libraries are required to parse XML. To simplify the XML processing requirements, advanced declarative languages such as XQuery and XPath came into being, which can meet the XML conditional query requirements, but the conditional…

The relational database data model is simple, and they are all single-level two-dimensional tables with clear rows and columns. It is relatively simple to use SQL. In MongoDB, there is a multi-level nested structure. The attribute fields appear arbitrarily, and it is not easy to describe which field information of…

One of the biggest differences between SQL and NoSQL databases is JOIN. Although MongoDB introduced $lookup as a supplement to the use of relational data in NoSQL databases, even if it is a simple two-table association, $lookup needs to be replaced with complex aggregate queries. The actual application environment is…

There are many JSON libraries available in Java. Most open-source packages completely deserialize JSON into Java objects and then access the property values of interest in the objects, such as Jackson, GSON, Genson, FastJson, and org.json. There is also a type of JSON library, such as JsonPATH. Java calls a…

MongoDB does not support SQL functions. The existing open-source MongoDB JDBC driver works on the principle that SQL queries are verified and converted to MongoDB queries and then executed by calling MongoDB Java API, which provides translation tools and services from SQL to MongoDB query language. In MongoDB, there is…

Java SE 8 introduces the Stream API. This new way of writing code is quite different from the previous way of processing collections. With only a filter, map, reduce, and iterate, you can write concise and expressive data processing queries. For this reason, many programmers try to replace SQL with…

Almost every Java programmer will create and process collections. They are the basis of programming. But if you often deal with SQL-like operations, for example, “find out classes with an average English score of less than 70”, “select CLASS, avg(English) as avg_En from students_scores group by CLASS having avg(English)<70”, most…

Java programs usually use the open-source package Apache POI to read data in Excel files. Although POI is powerful, it has a certain learning curve. For Excel files with a relatively regular format, if you can use Excel as a Java database, use SQL to calculate Data will be very…

Java programmers sometimes have to programmatically perform tasks of reading or writing Excel, usually by writing some custom programs to handle them. The open-source Apache POI package is a very useful tool for completing such tasks. POI provides two modes, HSSF and XSSF, to read, create, modify, and write XLS…