在Python中,格式化字符串时,我可以按名称而不是按位置填充占位符,如下所示:
print "There's an incorrect value '%(value)s' in column # %(column)d" % \
{ 'value': x, 'column': y }
我想知道这在Java中是否可能(希望没有外部库)?
在Python中,格式化字符串时,我可以按名称而不是按位置填充占位符,如下所示:
print "There's an incorrect value '%(value)s' in column # %(column)d" % \
{ 'value': x, 'column': y }
我想知道这在Java中是否可能(希望没有外部库)?
当前回答
在编写本文时,Java中还没有内置任何东西。我建议编写自己的实现。我的偏好是一个简单流畅的构建器接口,而不是创建一个映射并将其传递给函数——你最终会得到一个漂亮的连续代码块,例如:
String result = new TemplatedStringBuilder("My name is {{name}} and I from {{town}}")
.replace("name", "John Doe")
.replace("town", "Sydney")
.finish();
下面是一个简单的实现:
class TemplatedStringBuilder {
private final static String TEMPLATE_START_TOKEN = "{{";
private final static String TEMPLATE_CLOSE_TOKEN = "}}";
private final String template;
private final Map<String, String> parameters = new HashMap<>();
public TemplatedStringBuilder(String template) {
if (template == null) throw new NullPointerException();
this.template = template;
}
public TemplatedStringBuilder replace(String key, String value){
parameters.put(key, value);
return this;
}
public String finish(){
StringBuilder result = new StringBuilder();
int startIndex = 0;
while (startIndex < template.length()){
int openIndex = template.indexOf(TEMPLATE_START_TOKEN, startIndex);
if (openIndex < 0){
result.append(template.substring(startIndex));
break;
}
int closeIndex = template.indexOf(TEMPLATE_CLOSE_TOKEN, openIndex);
if(closeIndex < 0){
result.append(template.substring(startIndex));
break;
}
String key = template.substring(openIndex + TEMPLATE_START_TOKEN.length(), closeIndex);
if (!parameters.containsKey(key)) throw new RuntimeException("missing value for key: " + key);
result.append(template.substring(startIndex, openIndex));
result.append(parameters.get(key));
startIndex = closeIndex + TEMPLATE_CLOSE_TOKEN.length();
}
return result.toString();
}
}
其他回答
谢谢你的帮助!使用所有的线索,我写了一个例程来做我想要的——使用字典的类似python的字符串格式化。因为我是Java新手,任何提示都是感激的。
public static String dictFormat(String format, Hashtable<String, Object> values) {
StringBuilder convFormat = new StringBuilder(format);
Enumeration<String> keys = values.keys();
ArrayList valueList = new ArrayList();
int currentPos = 1;
while (keys.hasMoreElements()) {
String key = keys.nextElement(),
formatKey = "%(" + key + ")",
formatPos = "%" + Integer.toString(currentPos) + "$";
int index = -1;
while ((index = convFormat.indexOf(formatKey, index)) != -1) {
convFormat.replace(index, index + formatKey.length(), formatPos);
index += formatPos.length();
}
valueList.add(values.get(key));
++currentPos;
}
return String.format(convFormat.toString(), valueList.toArray());
}
我是一个小型库的作者,它可以做你想要的:
Student student = new Student("Andrei", 30, "Male");
String studStr = template("#{id}\tName: #{st.getName}, Age: #{st.getAge}, Gender: #{st.getGender}")
.arg("id", 10)
.arg("st", student)
.format();
System.out.println(studStr);
或者你可以串起参数:
String result = template("#{x} + #{y} = #{z}")
.args("x", 5, "y", 10, "z", 15)
.format();
System.out.println(result);
// Output: "5 + 10 = 15"
你可以在字符串助手类上有这样的东西
/**
* An interpreter for strings with named placeholders.
*
* For example given the string "hello %(myName)" and the map <code>
* <p>Map<String, Object> map = new HashMap<String, Object>();</p>
* <p>map.put("myName", "world");</p>
* </code>
*
* the call {@code format("hello %(myName)", map)} returns "hello world"
*
* It replaces every occurrence of a named placeholder with its given value
* in the map. If there is a named place holder which is not found in the
* map then the string will retain that placeholder. Likewise, if there is
* an entry in the map that does not have its respective placeholder, it is
* ignored.
*
* @param str
* string to format
* @param values
* to replace
* @return formatted string
*/
public static String format(String str, Map<String, Object> values) {
StringBuilder builder = new StringBuilder(str);
for (Entry<String, Object> entry : values.entrySet()) {
int start;
String pattern = "%(" + entry.getKey() + ")";
String value = entry.getValue().toString();
// Replace every occurence of %(key) with value
while ((start = builder.indexOf(pattern)) != -1) {
builder.replace(start, start + pattern.length(), value);
}
}
return builder.toString();
}
有Java插件使用字符串插值在Java(像在Kotlin, JavaScript)。支持Java 8,9,10,11…https://github.com/antkorwin/better-strings
在字符串字面量中使用变量:
int a = 3;
int b = 4;
System.out.println("${a} + ${b} = ${a+b}");
使用表达式:
int a = 3;
int b = 4;
System.out.println("pow = ${a * a}");
System.out.println("flag = ${a > b ? true : false}");
使用功能:
@Test
void functionCall() {
System.out.println("fact(5) = ${factorial(5)}");
}
long factorial(int n) {
long fact = 1;
for (int i = 2; i <= n; i++) {
fact = fact * i;
}
return fact;
}
更多信息,请阅读项目README。
您应该看看官方的ICU4J库。它提供了一个类似于JDK的MessageFormat类,但前者支持命名占位符。
与本页提供的其他解决方案不同。ICU4j是ICU项目的一部分,由IBM维护并定期更新。此外,它还支持高级用例,如多元化等。
下面是一个代码示例:
MessageFormat messageFormat =
new MessageFormat("Publication written by {author}.");
Map<String, String> args = Map.of("author", "John Doe");
System.out.println(messageFormat.format(args));