检查Java中的两个参数,要么都不为null,要么优雅为null

我使用spring boot来开发用于发送电子邮件的shell项目,例如

sendmail -from foo@bar.com -password  foobar -subject "hello world"  -to aaa@bbb.com

如果缺少from和password参数,我使用默认的发件人和密码,例如noreply@bar.com和123456.

因此,如果用户传递from参数,他们也必须传递password参数,反之亦然.也就是说,两者都是非null,或者两者都是null.

我该如何优雅地检查？

现在我的方式是

if ((from != null && password == null) || (from == null && password != null)) {
    throw new RuntimeException("from and password either both exist or both not exist");
}

coolguy.. 323

有一种使用^(XOR)运算符的方法:

if (from == null ^ password == null) {
    // Use RuntimeException if you need to
    throw new IllegalArgumentException("message");
}

该if要是只有一个变量是空的条件将是真实的.

但我认为通常最好使用if具有不同异常消息的两个条件.您无法使用单个条件定义出错的地方.

if ((from == null) && (password != null)) {
    throw new IllegalArgumentException("If from is null, password must be null");
}
if ((from != null) && (password == null)) {
    throw new IllegalArgumentException("If from is not null, password must not be null");
}

它更易读,更容易理解,只需要额外输入一点.

有一种使用^(XOR)运算符的方法:

if (from == null ^ password == null) {
    // Use RuntimeException if you need to
    throw new IllegalArgumentException("message");
}

该if要是只有一个变量是空的条件将是真实的.

但我认为通常最好使用if具有不同异常消息的两个条件.您无法使用单个条件定义出错的地方.

if ((from == null) && (password != null)) {
    throw new IllegalArgumentException("If from is null, password must be null");
}
if ((from != null) && (password == null)) {
    throw new IllegalArgumentException("If from is not null, password must not be null");
}

它更易读,更容易理解,只需要额外输入一点.

好吧,听起来你正试图检查两者的"无效"状态是否相同.你可以使用:

if ((from == null) != (password == null))
{
    ...
}

或者使用辅助变量使其更明确:

boolean gotFrom = from != null;
boolean gotPassword = password != null;
if (gotFrom != gotPassword)
{
    ...
}

就个人而言,我更喜欢可读性和优雅.

if (from != null && password == null) {
    throw new RuntimeException("-from given without -password");
}
if (from == null && password != null) {
    throw new RuntimeException("-password given without -from");
}

将该功能放在带有签名的2参数方法中:

void assertBothNullOrBothNotNull(Object a, Object b) throws RuntimeException

这节省了您感兴趣的实际方法的空间并使其更具可读性.稍微冗长的方法名称没有任何问题,并且非常简短的方法没有任何问题.

Objects.isNull(Object)假设静态导入,将使用Java 8解决方案:

if (isNull(from) != isNull(password)) {
    throw ...;
}

对于Java <8(或者如果您不喜欢使用Objects.isNull()),您可以轻松编写自己的isNull()方法.

这是任何数量的空检查的一般解决方案

public static int nulls(Object... objs)
{
    int n = 0;
    for(Object obj : objs) if(obj == null) n++;
    return n;
}

public static void main (String[] args) throws java.lang.Exception
{
    String a = null;
    String b = "";
    String c = "Test";

    System.out.println (" "+nulls(a,b,c));
}

用途

// equivalent to (a==null & !(b==null|c==null) | .. | c==null & !(a==null|b==null))
if (nulls(a,b,c) == 1) { .. }

// equivalent to (a==null | b==null | c==null)
if (nulls(a,b,c) >= 1) { .. }

// equivalent to (a!=null | b!=null | c!=null)
if (nulls(a,b,c) < 3) { .. }

// equivalent to (a==null & b==null & c==null)
if (nulls(a,b,c) == 3) { .. }

// equivalent to (a!=null & b!=null & c!=null)
if (nulls(a,b,c) == 0) { .. }

由于您希望在发送者和密码都不存在时执行特殊操作(使用默认值),请先处理.
之后,您应该同时拥有发件人和密码来发送电子邮件; 如果丢失则抛出异常.

// use defaults if neither is provided
if ((from == null) && (password == null)) {
    from = DEFAULT_SENDER;
    password = DEFAULT_PASSWORD;
}

// we should have a sender and a password now
if (from == null) {
    throw new MissingSenderException();
}
if (password == null) {
    throw new MissingPasswordException();
}

if( from != null )
{
    if( password == null )
        error( "password required for " + from );
}
else
{
    if( password != null )
        warn( "the given password will not be used" );
}

if(from != null && password != null){
    //use the provided values
} else if(from == null && password == null){
    //both values are null use the default values
} else{
   //throw an exception because the input is not correct.
}

throw new IllegalArgumentException("form of " + form + 
    " cannot be used with a "
    + (password==null?"null":"not null") +  
    " password. Either provide a value for both, or no value for both"
);

private void validatePasswordExists(Parameters params) {
   if (!params.hasKey("password")){
      throw new PasswordMissingException("Password missing");
   }
}

private void validateFromExists(Parameters params) {
   if (!params.hasKey("from")){
      throw new FromEmailMissingException("From-email missing");
   }
}

private void validateParams(Parameters params) {

  if (params.hasKey("from") || params.hasKey("password")){
     validateFromExists(params);
     validatePasswordExists(params);
  }
}

if (a==null? b!=null:b==null)

if (from == null) { // form is null, ignore given password here
    // use your own defaults
} else if (password == null) { // form is given but password is not
    // throw exception
} else { // both arguments are given
    // use given arguments
}