GETTING STARTED WITH JSqlParser

The goal of JSqlParser is to translate a SQL string into a hierarchy of Java classes, i.e. an abstract syntax tree. 

The syntax of SQL  is quite complex, and so is the tree generated by JSqlParser. In the beginning it is a good idea to focus only on a small subset of constructs, and see how they get translated into a tree.

We start from arithmetic expressions: the code below shows how to parse and process strings like "32+(21-4)".

//-----------------------------------------------------------------------------------------------------
package edu.buffalo.cse562.sql.expression;

import java.io.StringReader;
import net.sf.jsqlparser.expression.*;
import net.sf.jsqlparser.parser.*;

public class ExpressionExample 
{
    public static void main(String[] args) throws ParseException
    {
        String str = "1-(3+2)";
        Expression arithmeticExpr = parseArithmeticExpression(str);
        SimpleCalculator calculator = new SimpleCalculator();
        arithmeticExpr.accept(calculator);
        System.out.println(str+" = "+calculator.getResult());
    }
    
    /**
     * 
     * Parse something like "(3+2)-A"
     * 
     * @param exprStr
     * @return
     * @throws ParseException 
     */
    public static Expression parseArithmeticExpression(String exprStr) throws ParseException
    {
        CCJSqlParser parser = new CCJSqlParser(new StringReader(exprStr));
        return parser.SimpleExpression();
    }
    
    
    /**
     * 
     * Parse something like "A<B*10"
     * 
     * @param exprStr
     * @return
     * @throws ParseException 
     */
    public static Expression parseGeneralExpression(String exprStr) throws ParseException
    {
        CCJSqlParser parser = new CCJSqlParser(new StringReader(exprStr));
        return parser.Expression();
    }
}

//-----------------------------------------------------------------------------------------------------

package edu.buffalo.cse562.sql.expression;

import net.sf.jsqlparser.expression.*;
import net.sf.jsqlparser.expression.operators.arithmetic.*;

/**
 *
 * @author Niccolo' Meneghetti
 */
public class SimpleCalculator extends AbstractExpressionVisitor
{
    private long accumulator;
    
    public long getResult()
    { return accumulator; }

    @Override
    public void visit(LongValue lv)
    { accumulator=lv.getValue(); }
    

    @Override
    public void visit(Addition adtn) 
    {
        adtn.getLeftExpression().accept(this);
        long leftValue = accumulator;
        adtn.getRightExpression().accept(this);
        long rightValue = accumulator;
        accumulator=(leftValue+rightValue);
    }

    @Override
    public void visit(Subtraction s) 
    {
        s.getLeftExpression().accept(this);
        long leftValue = accumulator;
        s.getRightExpression().accept(this);
        long rightValue = accumulator;
        accumulator=(leftValue-rightValue);
    }

    @Override
    public void visit(Parenthesis prnths) 
    { prnths.getExpression().accept(this); }
    
    
}

//-----------------------------------------------------------------------------------------------------

package edu.buffalo.cse562.sql.expression;

import net.sf.jsqlparser.expression.*;
import net.sf.jsqlparser.expression.operators.arithmetic.*;
import net.sf.jsqlparser.expression.operators.conditional.*;
import net.sf.jsqlparser.expression.operators.relational.*;
import net.sf.jsqlparser.schema.Column;
import net.sf.jsqlparser.statement.select.SubSelect;

/**
 *
 * Default behavior for ExpressionVisitors: raise UnsupportedOperationException
 * 
 * @author Niccolo' Meneghetti
 */
public class AbstractExpressionVisitor implements ExpressionVisitor
{

    @Override
    public void visit(NullValue nv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Function fnctn) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(InverseExpression ie) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(JdbcParameter jp) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(DoubleValue dv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(LongValue lv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(DateValue dv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(TimeValue tv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(TimestampValue tv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Parenthesis prnths) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(StringValue sv) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Addition adtn) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Division dvsn) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Multiplication m) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Subtraction s) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(AndExpression ae) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(OrExpression oe) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Between btwn) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(EqualsTo et) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(GreaterThan gt) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(GreaterThanEquals gte) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(InExpression ie) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(IsNullExpression ine) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(LikeExpression le) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(MinorThan mt) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(MinorThanEquals mte) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(NotEqualsTo net) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Column column) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(SubSelect ss) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(CaseExpression ce) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(WhenClause wc) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(ExistsExpression ee) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(AllComparisonExpression ace) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(AnyComparisonExpression ace) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Concat concat) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(Matches mtchs) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(BitwiseAnd ba) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(BitwiseOr bo) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }

    @Override
    public void visit(BitwiseXor bx) {
        throw new UnsupportedOperationException("Not supported yet."); 
    }
    
}

//-----------------------------------------------------------------------------------------------------

Things to understand about JSqlParser:

1) Most of the methods of net.sf.jsqlparser.parser.CCJSqlParser are used to parse sub-grammars of SQL. Statement() is the most general one, and will parse an arbitrary SQL command.
2) Once you obtained an abstract syntax tree, you should process it using a Visitor, i.e. implementing one of the Visitor interfaces (like we did with SimpleCalculator)

Where to go from here?

Try to generalize the SimpleCalculator visitor in order to support arbitrary expressions, like those provided by the 'parseGeneralExpression' method. Explore the ExpressionVisitor interface, and find out which methods need to be implemented.