PlaceholderProperties.java

PlaceholderProperties.java

import java.util.Properties;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class PlaceholderProperties extends Properties {
    private static final long serialVersionUID = 1L;
    private static final Pattern PARAMETER_PATTERN = Pattern.compile("\\$\\{([^}]*)\\}");

    public PlaceholderProperties() {
        super();
    }

    public PlaceholderProperties(Properties properties) {
        super(properties);
    }

    @Override
    public String getProperty(String key) {
        String value = super.getProperty(key);
        return getRealValue(value);
    }

    @Override
    public String getProperty(String key, String defaultValue) {
        String value = super.getProperty(key);
        return value == null ? defaultValue : getRealValue(value);
    }
    
    // 获取子属性
    public Properties getProperties(String prefix) {
        Properties props = new Properties();
        prefix = prefix + '.';
        for (Map.Entry<?, ?> entry : entrySet()) {
            Object name = entry.getKey();
            if (name instanceof String) {
                String key = (String) name;
                if (key.startsWith(prefix)) {
                    String value = this.getProperty(name);
                    if (value != null) {
                        key = key.substring(prefix.length());
                        props.put(key, value);
                    }
                }
            }
        }
        return props;
    }

    // 根据 System.getProperty() 替换变量
    private String getRealValue(String value) {
        if (value == null) {
            return null;
        }
        if (value.indexOf('$') >= 0) {
            Matcher matcher = PARAMETER_PATTERN.matcher(value);
            StringBuffer sb = new StringBuffer();
            while (matcher.find()) {
                String name = matcher.group(1);
                String val = this.getProperty(name);
                if (val == null) {
                    val = System.getProperty(name);
                }
                if (val == null) {
                    // 找不到变量值，保存原始文本不变
                    val = matcher.group();
                }
                matcher.appendReplacement(sb, Matcher.quoteReplacement(val));
            }
            matcher.appendTail(sb);
            value = sb.toString();
        }
        return value;
    }
}