java - StringBuilder.append(String str); 发生了一些疯狂的事情；

Question

我的 java 项目有问题。

以下函数应该为 SQL 语句传递一个字符串:

private static String createInsertString(Pat p)
{   
    StringBuilder x = new StringBuilder();


    x.append(""  + p.getPatnr() +","+ p.getSvnr());

    java.sql.Date andat = null,gebdat;

    if(p.getAndat()==null)
        andat=null;
    else
        andat=new java.sql.Date(p.getAndat().getTimeInMillis());

    if(p.getGebdat()==null)
        gebdat=null;
    else
        gebdat=new java.sql.Date(p.getGebdat().getTimeInMillis());

    x.append("," + andat==null?"null":andat);
    x.append("," + p.getTele()==null?"null":p.getTele());
    x.append("," + p.getVName() +","+ p.getNname());
    x.append("," + p.getKk()==null?"null":p.getKk());
    x.append("," + gebdat==null?"null":gebdat);
    x.append("," + p.getAdrplzort()==null?"null":6);
    x.append("," + p.getAdrstr()==null?"null":p.getAdrstr());
    x.append("," + p.getAdrhnr()==null?"null":p.getAdrhnr());
    s.append("," + p.getReplzort()==null?"null":p.getReplzort().getPlzortnr());
    x.append("," + p.getRestr()==null?"null":p.getRestr());
    x.append("," + p.getRehnr()==null?"null":p.getRehnr());
    x.append("," + p.getLevel());
    x.append("," + p.getCon()==null?"null":p.getCon());
    x.append("," + (p.isPa()?"y":"n")+","+ (p.isLonly()?"y":"n") +","+ (p.isGest()?"y":"n"));
    x.append("," + p.getBem()==null?"null":p.getBem());
    x.append("," + (p.isKat1()?'y':'n') +","+ (p.isKat2()?'y':'n') +","+ (p.isKat3()?'y':'n'));

    System.out.println(x);

    return x.toString();
} 

输出为

6,6465136nullnull,Jürgen,Wieslernullnull6nullnullnullnull,0null,n,n,nnull,n,n,n

但它应该是这样的:

6,6465136,null,null,Jürgen,Wiesler,null,null,6,null,null,null,null,0,null,n,n,n,null,n,n,n

有人有想法吗？我在 debian(64 位)上使用 jdk 1.7

Answer 1

问题在于运算符如何绑定(bind)。看看这个:

x.append("," + andat==null?"null":andat);

现在将其视为:

x.append(("," + andat) == null ? "null" : andat);

LHS永远不会为空，所以它总是只是附加andat...并且仍然转换为“null”如果引用为 null，因为这是 StringBuilder 的默认行为。

您的代码比它需要的复杂得多，而且效率低下。考虑将其重写为:

private static String createInsertString(Pat p)
{   
    StringBuilder x = new StringBuilder();
    java.sql.Date andat = p.andat == null ? null 
        : new java.sql.Date(p.getAndat().getTimeInMillis());
    java.sql.Date gebdat = p.getGebdat() == null ? null 
        : new java.sql.Date(p.getGebdat().getTimeInMillis());

    x.append(p.getPatnr()).append(",")
     .append(p.getSvnr()).append(",")
     .append(andat).append(",")
     .append(p.getTele()).append(",")

     // etc

    return x.toString();
}

请注意，我认为您在原始版本中存在错误:

x.append("," + p.getVName() +","+ p.getNname());

这些意味着在哪里调用两个不同的 getter？