java - 如何生成随机码并检查它是否存在于数据库中

Question

我尝试生成随机代码名称作为 licenseKey 并检查它是否存在于数据库中。如果不存在，则显示在我的jsp页面中，如果存在，则继续生成随机代码。我收到错误“java.lang.StackOverflowError”。如何解决这个问题？下面是我的代码:

package com.raydar.hospital;
import com.raydar.hospital.DB_Connection;
import java.sql.*;

public class RandomCodeGenerator {


String licenseKey = "";

int noOfCAPSAlpha = 4;
int noOfDigits = 4;
int minLen = 8;
int maxLen = 8;

char[] code = RandomCode.generateCode(minLen, maxLen, noOfCAPSAlpha, noOfDigits);


public RandomCodeGenerator(){
}


public String getOutputCode() throws Exception{

    String result ="";

    result = isLicenseKeyExist();
    System.out.println("4 + " +result);

    if (result=="false"){

        System.out.println("1 + " +new String(code));

        licenseKey = new String(code);
    }

    else if (result=="true"){

            System.out.println("2 + " +new String(code));

            licenseKey = new String(code);

                isLicenseKeyExist ();         
        }           

    return licenseKey;
}



private String isLicenseKeyExist () throws Exception{
    String code = "";
    code = getOutputCode();

    Connection connection = null;
    Statement statement = null;
    ResultSet rs = null;
    String result="";
    System.out.println("3 + " +code);

    try{
    DB_Connection connect = new DB_Connection();

    connection = connect.getDBConnection();
    statement = connection.createStatement();
    rs = statement.executeQuery("SELECT licenseKey FROM hospital WHERE licenseKey = '" +code+ "'");
    if (rs.next()){    

    result = "true";

    }

    else{

        result = "false";

    }

    }catch (Exception e){
    System.out.println("Error retrieving data! "+e);

}

    return result;

}

Answer 1

您创建一个递归循环，其中 isLicenseKeyExist() 调用 getOutputCode()，然后 getOutputCode() 调用 isLicenseKeyExist()。所以最终你用完了堆栈空间，并得到这个异常。

这里，

public String getOutputCode() throws Exception{
    String result ="";
    result = isLicenseKeyExist();
   ...

private String isLicenseKeyExist () throws Exception{
    String code = "";
    code = getOutputCode();
...
}