如何使用bean中的属性格式化字符串 [英] How do I format a string with properties from a bean

问题描述

我想使用格式创建一个String，用bean中的属性替换格式的一些标记。有没有一个支持这个的库，或者我将不得不创建自己的实现？

I want to create a String using a format, replacing some tokens in the format with properties from a bean. Is there a library that supports this or am I going to have to create my own implementation?

让我用一个例子来演示。假设我有一个bean Person ;

Let me demonstate with an example. Say I have a bean Person;

public class Person {
  private String id;
  private String name;
  private String age;

  //getters and setters
}

我想要能够指定类似的格式字符串;

I want to be able to specify format strings something like;

"{name} is {age} years old."
"Person id {id} is called {name}."

并使用bean中的值自动填充格式占位符，例如;

and automatically populate the format placeholders with values from the bean, something like;

String format = "{name} is {age} old."
Person p = new Person(1, "Fred", "32 years");
String formatted = doFormat(format, person); //returns "Fred is 32 years old."

我看过 MessageFormat 但这似乎只允许我传递数字索引，而不是bean属性。

I've had a look at MessageFormat but this only seems to allow me to pass numeric indexes, not bean properties.

推荐答案

滚动我自己，现在进行测试。欢迎评论。

Rolled my own, testing now. Comments welcome.

import java.lang.reflect.Field;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class BeanFormatter<E> {

  private Matcher matcher;
  private static final Pattern pattern = Pattern.compile("\\{(.+?)\\}");

  public BeanFormatter(String formatString) {
    this.matcher = pattern.matcher(formatString);
  }

  public String format(E bean) throws Exception {
    StringBuffer buffer = new StringBuffer();

    try {
      matcher.reset();
      while (matcher.find()) {
        String token = matcher.group(1);
        String value = getProperty(bean, token);
        matcher.appendReplacement(buffer, value);
      }
      matcher.appendTail(buffer);
    } catch (Exception ex) {
      throw new Exception("Error formatting bean " + bean.getClass() + " with format " + matcher.pattern().toString(), ex);
    }
    return buffer.toString();
  }

  private String getProperty(E bean, String token) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
    Field field = bean.getClass().getDeclaredField(token);
    field.setAccessible(true);
    return String.valueOf(field.get(bean));
  }

  public static void main(String[] args) throws Exception {
    String format = "{name} is {age} old.";
    Person p = new Person("Fred", "32 years", 1);

    BeanFormatter<Person> bf = new BeanFormatter<Person>(format);
    String s = bf.format(p);
    System.out.println(s);
  }

}

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