当我在一个Java应用程序中工作时,我最近需要组装一个以逗号分隔的值列表,以传递给另一个web服务,而不知道预先会有多少个元素。我能想到的最好的是这样的:
public String appendWithDelimiter( String original, String addition, String delimiter ) {
if ( original.equals( "" ) ) {
return addition;
} else {
return original + delimiter + addition;
}
}
String parameterString = "";
if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," );
if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," );
我意识到这不是特别有效,因为到处都在创建字符串,但我追求的是清晰而不是优化。
在Ruby中,我可以这样做,这感觉要优雅得多:
parameterArray = [];
parameterArray << "elementName" if condition;
parameterArray << "anotherElementName" if anotherCondition;
parameterString = parameterArray.join(",");
但是由于Java缺少join命令,我找不到任何等价的命令。
那么,在Java中最好的方法是什么呢?
//Note: if you have access to Java5+,
//use StringBuilder in preference to StringBuffer.
//All that has to be replaced is the class name.
//StringBuffer will work in Java 1.4, though.
appendWithDelimiter( StringBuffer buffer, String addition,
String delimiter ) {
if ( buffer.length() == 0) {
buffer.append(addition);
} else {
buffer.append(delimiter);
buffer.append(addition);
}
}
StringBuffer parameterBuffer = new StringBuffer();
if ( condition ) {
appendWithDelimiter(parameterBuffer, "elementName", "," );
}
if ( anotherCondition ) {
appendWithDelimiter(parameterBuffer, "anotherElementName", "," );
}
//Finally, to return a string representation, call toString() when returning.
return parameterBuffer.toString();
您可以编写一个连接风格的实用程序方法,它可以在java.util.Lists上工作
public static String join(List<String> list, String delim) {
StringBuilder sb = new StringBuilder();
String loopDelim = "";
for(String s : list) {
sb.append(loopDelim);
sb.append(s);
loopDelim = delim;
}
return sb.toString();
}
然后像这样使用它:
List<String> list = new ArrayList<String>();
if( condition ) list.add("elementName");
if( anotherCondition ) list.add("anotherElementName");
join(list, ",");