SoFunction
Updated on 2025-04-14

Detailed explanation of how Java parses and generates SQL

1. What is JSQLParser

JSQLParser is an open source Java library for parsing SQL statements and converting them into an abstract syntax tree (AST). It supports a variety of SQL dialects, including MySQL, PostgreSQL, Oracle, and SQL Server. JSQLParser enables developers to easily analyze, modify and generate SQL statements, and is widely used in scenarios such as database tools, ORM frameworks, and data migration tools.

Main functions

SQL parsing: JSQLParser can parse SQL query strings into structured object models, which facilitates subsequent operations and analysis.

Abstract Syntax Tree (AST): The parsed SQL statement is represented in the form of AST. Developers can access these objects to obtain various components of SQL statements, such as selecting fields, table names, conditions, etc.

SQL Generation: In addition to parsing, JSQLParser also supports regenerating SQL statements from AST, which is very useful for dynamically building SQL queries.

Supports multiple SQL dialects: JSQLParser supports a variety of SQL dialects, and developers can choose the appropriate dialect for parsing according to their needs.

Flexible scalability:JSQLParser provides rich APIs that allow developers to scale and customize the behavior of parsers based on specific needs.

Use scenarios

Database Tools: In the database management tool, JSQLParser can be used to parse SQL queries input by users, providing syntax highlighting, automatic completion and other functions.

ORM framework: In the Object Relational Mapping (ORM) framework, JSQLParser can help convert object models into SQL queries and parse SQL result sets.

Data migration and conversion: In the data migration tool, JSQLParser can parse the SQL statements of the source database and generate the SQL statements required for the target database.

SQL Optimization: By analyzing SQL statements, developers can analyze the performance of the query and optimize it.

4. How to use JSQLParser

Introduce dependencies

In a Maven project, you can introduce JSQLParser through the following dependencies:

<dependency>
    <groupId></groupId>
    <artifactId>jsqlparser</artifactId>
    <version>3.2</version>
</dependency>

Parsing SQL statements

package ;

import ;
import ;
import ;
import ;
import ;
import ;

import ;

public class SqlParserExample {
    public static void main(String[] args) {
        // SQL query to be parsed
        String sql = "SELECT id, name FROM users WHERE age > 30";
        try {
            // Parse the SQL statement
            Statement statement = (sql);
            
            // Ensure the parsed statement is a SELECT statement
            if (statement instanceof Select) {
                Select selectStatement = (Select) statement;
                PlainSelect plainSelect = (PlainSelect) ();

                // Get the selected columns
                List<SelectItem> selectItems = ();
                ("Selected columns:");
                for (SelectItem item : selectItems) {
                    (item);
                }

                // Get the WHERE condition
                Expression where = ();
                ("WHERE condition:");
                if (where != null) {
                    (where);
                } else {
                    ("No WHERE condition");
                }
            }
        } catch (Exception e) {
            (); // Print the stack trace in case of an exception
        }
    }
}

Code Explanation

  • Package Declaration: The code is part of the package.
  • Imports: Necessary classes from the JSQLParser library are imported to handle SQL parsing.
  • Main Class: The SqlParserExample class contains the main method, which is the entry point of the program.
  • SQL Query: A SQL query string is defined for parsing.
  • Parsing the SQL Statement: The SQL string is parsed using (sql).
  • Checking Statement Type: The code checks if the parsed statement is an instance of Select.
  • Getting Selected Columns: The selected columns are retrieved from the PlainSelect object and printed to the console.
  • Getting WHERE Condition: The WHERE condition is retrieved and printed. If there is no WHERE condition, a corresponding message is displayed.
  • Exception Handling: Any exceptions that occur during parsing are caught and printed to the console.

This code effectively demonstrates how to parse a SQL SELECT statement and extract the selected columns and WHERE conditions using JSQLParser.

Generate SQL statements

package ;

import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ; // Ensure SelectExpressionItem class is imported

import ;
import ;

public class SqlGeneratorExample {
    public static void main(String[] args) {
        // Create a Select object
        Select select = new Select();
        
        // Create a PlainSelect object
        PlainSelect plainSelect = new PlainSelect();
        
        // Set the selected columns
        List<SelectItem> selectItems = new ArrayList<>();
        (new SelectExpressionItem(new Column("id"))); // Use Column class for "id"
        (new SelectExpressionItem(new Column("name"))); // Use Column class for "name"
        (selectItems);
        
        // Set the table
        Table table = new Table("users");
        (table);
        
        // Set the WHERE condition
        BinaryExpression whereCondition = new GreaterThan(); // Create a GreaterThan expression
        (new Column("id")); // Set the left expression to the "id" column
        (new LongValue(10)); // Set the right expression to a LongValue of 10
        (whereCondition);
        
        // Set the PlainSelect as the SelectBody
        (plainSelect);
        
        // Generate the SQL statement
        String generatedSql = ();
        (generatedSql); // Print the generated SQL statement
    }
}

Code Explanation

  • Package Declaration: The code is part of the package.
  • Imports: Necessary classes from the JSQLParser library are imported to handle SQL generation.
  • Main Class: The SqlGeneratorExample class contains the main method, which is the entry point of the program.
  • Creating Select Object: A Select object is created to represent the SQL SELECT statement.
  • Creating PlainSelect Object: A PlainSelect object is created to define the details of the SELECT statement.
  • Setting Selected Columns: A list of SelectItem objects is created to hold the selected columns. Each column is added using the SelectExpressionItem class.
  • Setting Table: A Table object is created to specify the table from which to select data.
  • Setting WHERE Condition: A GreaterThan expression is created to define the WHERE condition. The left expression is set to the “id” column, and the right expression is set to a LongValue of 10.
  • Setting SelectBody: The PlainSelect object is set as the body of the Select statement.
  • Generating SQL Statement: The SQL statement is generated by calling toString() on the Select object, and the generated SQL is printed to the console.

The above are just some key codes. Please refer to the code repository below.

Code Repository

/Harries/Java-demo(JSQLParser)

Pros and cons of JSQLParser

advantage：

  • Open source and free to use.
  • Supports multiple SQL dialects and is highly flexible.
  • Provides rich APIs for easy scalability and customization.

shortcoming：

  • For complex SQL statements, parsing may have some limitations.
  • A certain learning curve is required, especially for beginners.

Summarize

JSQLParser is a powerful SQL parsing tool for a variety of Java applications. Whether it is a database management tool, an ORM framework or a data migration tool, JSQLParser can provide efficient SQL parsing and generation capabilities. With flexible APIs and support for a variety of SQL dialects, developers can easily process SQL statements and improve development efficiency.

This is the end of this article about how to analyze and generate sql in Java. For more related java parsing and generating sql content, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!