ANTLR是一个强大的工具,可以用来生成SQL解析器,从而生成抽象语法树(AST)。下面是一个简单的示例,展示如何使用ANTLR来生成SQL解析器并生成AST:
grammar SQL;
query: selectStatement;
selectStatement: SELECT selectList FROM table;
selectList: (column (',' column)*) | '*';
column: ID;
table: ID;
SELECT: 'SELECT';
FROM: 'FROM';
ID: [a-zA-Z_][a-zA-Z0-9_]*;
WS: [ \t\r\n]+ -> skip;
antlr4 SQL.g
import org.antlr.v4.runtime.tree.ParseTree;
import org.antlr.v4.runtime.tree.TerminalNode;
public class SQLListenerImpl extends SQLBaseListener {
@Override
public void enterSelectStatement(SQLParser.SelectStatementContext ctx) {
System.out.println("Enter select statement: " + ctx.getText());
}
@Override
public void exitSelectStatement(SQLParser.SelectStatementContext ctx) {
System.out.println("Exit select statement: " + ctx.getText());
}
@Override
public void visitTerminal(TerminalNode node) {
System.out.println("Terminal: " + node.getText());
}
}
import org.antlr.v4.runtime.ANTLRInputStream;
import org.antlr.v4.runtime.CommonTokenStream;
import org.antlr.v4.runtime.tree.ParseTree;
public class Main {
public static void main(String[] args) {
String sql = "SELECT col1, col2 FROM table1";
SQLLexer lexer = new SQLLexer(new ANTLRInputStream(sql));
CommonTokenStream tokens = new CommonTokenStream(lexer);
SQLParser parser = new SQLParser(tokens);
ParseTree tree = parser.query();
SQLListenerImpl listener = new SQLListenerImpl();
ParseTreeWalker.DEFAULT.walk(listener, tree);
}
}
以上是一个简单的示例,演示了如何使用ANTLR来生成SQL解析器并生成AST。更复杂的语法规则和处理逻辑可以根据具体需求进行扩展和修改。