Spring PropertyPlaceholderConfigurerResolver

• 类全路径: org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.PropertyPlaceholderConfigurerResolver

• 这个类是从 Properties 中获取属性

    private final class PropertyPlaceholderConfigurerResolver implements PlaceholderResolver {
        private final Properties props;
        private PropertyPlaceholderConfigurerResolver(Properties props) {
            this.props = props;
        }
        @Override
        @Nullable
        public String resolvePlaceholder(String placeholderName) {
            return PropertyPlaceholderConfigurer.this.resolvePlaceholder(placeholderName,
                    this.props, systemPropertiesMode);
        }
    }

• 详细方法如下

    @Nullable
    protected String resolvePlaceholder(String placeholder, Properties props, int systemPropertiesMode) {
        String propVal = null;
        if (systemPropertiesMode == SYSTEM_PROPERTIES_MODE_OVERRIDE) {
            propVal = resolveSystemProperty(placeholder);
        }
        if (propVal == null) {
            propVal = resolvePlaceholder(placeholder, props);
        }
        if (propVal == null && systemPropertiesMode == SYSTEM_PROPERTIES_MODE_FALLBACK) {
            propVal = resolveSystemProperty(placeholder);
        }
        return propVal;
    }

    @Nullable
    protected String resolvePlaceholder(String placeholder, Properties props) {
        return props.getProperty(placeholder);
    }

    @Nullable
    protected String resolveSystemProperty(String key) {
        try {
            String value = System.getProperty(key);
            if (value == null && this.searchSystemEnvironment) {
                value = System.getenv(key);
            }
            return value;
        }
        catch (Throwable ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("Could not access system property '" + key + "': " + ex);
            }
            return null;
        }
    }