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

这是一个旧的线程,但只是为了记录,你也可以使用Java 8风格,像这样:

public static String replaceParams(Map<String, String> hashMap, String template) {
    return hashMap.entrySet().stream().reduce(template, (s, e) -> s.replace("%(" + e.getKey() + ")", e.getValue()),
            (s, s2) -> s);
}

用法:

public static void main(String[] args) {
    final HashMap<String, String> hashMap = new HashMap<String, String>() {
        {
            put("foo", "foo1");
            put("bar", "bar1");
            put("car", "BMW");
            put("truck", "MAN");
        }
    };
    String res = replaceParams(hashMap, "This is '%(foo)' and '%(foo)', but also '%(bar)' '%(bar)' indeed.");
    System.out.println(res);
    System.out.println(replaceParams(hashMap, "This is '%(car)' and '%(foo)', but also '%(bar)' '%(bar)' indeed."));
    System.out.println(replaceParams(hashMap, "This is '%(car)' and '%(truck)', but also '%(foo)' '%(bar)' + '%(truck)' indeed."));
}

输出将是:

This is 'foo1' and 'foo1', but also 'bar1' 'bar1' indeed.
This is 'BMW' and 'foo1', but also 'bar1' 'bar1' indeed.
This is 'BMW' and 'MAN', but also 'foo1' 'bar1' + 'MAN' indeed.

其他回答

https://dzone.com/articles/java-string-format-examples字符串。format(inputString, [listOfParams])将是最简单的方法。字符串中的占位符可以按顺序定义。欲了解更多详细信息,请查看提供的链接。

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));

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();
}

可以使用Apache Commons StringSubstitutor。注意,StrSubstitutor已弃用。

import org.apache.commons.text.StringSubstitutor;
// ...
Map<String, String> values = new HashMap<>();
values.put("animal", "quick brown fox");
values.put("target", "lazy dog");
StringSubstitutor sub = new StringSubstitutor(values);
String result = sub.replace("The ${animal} jumped over the ${target}.");
// "The quick brown fox jumped over the lazy dog."

这个类支持为变量提供默认值。

String result = sub.replace("The number is ${undefined.property:-42}.");
// "The number is 42."

要使用递归变量替换,调用setEnableSubstitutionInVariables(true);。

Map<String, String> values = new HashMap<>();
values.put("b", "c");
values.put("ac", "Test");
StringSubstitutor sub = new StringSubstitutor(values);
sub.setEnableSubstitutionInVariables(true);
String result = sub.replace("${a${b}}");
// "Test"

试试Freemarker,模板库。