一个简单的数据库实现-一个简单的数据库实现

package top.guoziyang.mydb.backend.parser; import java.util.ArrayList; import java.util.List; import top.guoziyang.mydb.backend.parser.statement.Abort; import top.guoziyang.mydb.backend.parser.statement.Begin; import top.guoziyang.mydb.backend.parser.statement.Commit; import top.guoziyang.mydb.backend.parser.statement.Create; import top.guoziyang.mydb.backend.parser.statement.Delete; import top.guoziyang.mydb.backend.parser.statement.Drop; import top.guoziyang.mydb.backend.parser.statement.Insert; import top.guoziyang.mydb.backend.parser.statement.Select; import top.guoziyang.mydb.backend.parser.statement.Show; import top.guoziyang.mydb.backend.parser.statement.SingleExpression; import top.guoziyang.mydb.backend.parser.statement.Update; import top.guoziyang.mydb.backend.parser.statement.Where; import top.guoziyang.mydb.common.Error; public class Parser { public static Object Parse(byte[] statement) throws Exception { Tokenizer tokenizer = new Tokenizer(statement); String token = tokenizer.peek(); tokenizer.pop(); Object stat = null; Exception statErr = null; try { switch(token) { case "begin": stat = parseBegin(tokenizer); break; case "commit": stat = parseCommit(tokenizer); break; case "abort": stat = parseAbort(tokenizer); break; case "create": stat = parseCreate(tokenizer); break; case "drop": stat = parseDrop(tokenizer); break; case "select": stat = parseSelect(tokenizer); break; case "insert": stat = parseInsert(tokenizer); break; case "delete": stat = parseDelete(tokenizer); break; case "update": stat = parseUpdate(tokenizer); break; case "show": stat = parseShow(tokenizer); break; default: throw Error.InvalidCommandException; } } catch(Exception e) { statErr = e; } try { String next = tokenizer.peek(); if(!"".equals(next)) { byte[] errStat = tokenizer.errStat(); statErr = new RuntimeException("Invalid statement: " + new String(errStat)); } } catch(Exception e) { e.printStackTrace(); byte[] errStat = tokenizer.errStat(); statErr = new RuntimeException("Invalid statement: " + new String(errStat)); } if(statErr != null) { throw statErr; } return stat; } private static Show parseShow(Tokenizer tokenizer) throws Exception { String tmp = tokenizer.peek(); if("".equals(tmp)) { return new Show(); } throw Error.InvalidCommandException; } private static Update parseUpdate(Tokenizer tokenizer) throws Exception { Update update = new Update(); update.tableName = tokenizer.peek(); tokenizer.pop(); if(!"set".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); update.fieldName = tokenizer.peek(); tokenizer.pop(); if(!"=".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); update.value = tokenizer.peek(); tokenizer.pop(); String tmp = tokenizer.peek(); if("".equals(tmp)) { update.where = null; return update; } update.where = parseWhere(tokenizer); return update; } private static Delete parseDelete(Tokenizer tokenizer) throws Exception { Delete delete = new Delete(); if(!"from".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); String tableName = tokenizer.peek(); if(!isName(tableName)) { throw Error.InvalidCommandException; } delete.tableName = tableName; tokenizer.pop(); delete.where = parseWhere(tokenizer); return delete; } private static Insert parseInsert(Tokenizer tokenizer) throws Exception { Insert insert = new Insert(); if(!"into".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); String tableName = tokenizer.peek(); if(!isName(tableName)) { throw Error.InvalidCommandException; } insert.tableName = tableName; tokenizer.pop(); if(!"values".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } List<String> values = new ArrayList<>(); while(true) { tokenizer.pop(); String value = tokenizer.peek(); if("".equals(value)) { break; } else { values.add(value); } } insert.values = values.toArray(new String[values.size()]); return insert; } private static Select parseSelect(Tokenizer tokenizer) throws Exception { Select read = new Select(); List<String> fields = new ArrayList<>(); String asterisk = tokenizer.peek(); if("*".equals(asterisk)) { fields.add(asterisk); tokenizer.pop(); } else { while(true) { String field = tokenizer.peek(); if(!isName(field)) { throw Error.InvalidCommandException; } fields.add(field); tokenizer.pop(); if(",".equals(tokenizer.peek())) { tokenizer.pop(); } else { break; } } } read.fields = fields.toArray(new String[fields.size()]); if(!"from".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); String tableName = tokenizer.peek(); if(!isName(tableName)) { throw Error.InvalidCommandException; } read.tableName = tableName; tokenizer.pop(); String tmp = tokenizer.peek(); if("".equals(tmp)) { read.where = null; return read; } read.where = parseWhere(tokenizer); return read; } private static Where parseWhere(Tokenizer tokenizer) throws Exception { Where where = new Where(); if(!"where".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } tokenizer.pop(); SingleExpression exp1 = parseSingleExp(tokenizer); where.singleExp1 = exp1; String logicOp = tokenizer.peek(); if("".equals(logicOp)) { where.logicOp = logicOp; return where; } if(!isLogicOp(logicOp)) { throw Error.InvalidCommandException; } where.logicOp = logicOp; tokenizer.pop(); SingleExpression exp2 = parseSingleExp(tokenizer); where.singleExp2 = exp2; if(!"".equals(tokenizer.peek())) { throw Error.InvalidCommandException; } return where; } private static SingleExpression parseSingleExp(Tokenizer tokenizer) throws Exception { SingleExpression exp = new SingleExpression(); String field = tokenizer.peek(); if(!isName(field)) { throw Error.InvalidCommandException; } exp.field = fi