功能介绍:
Property字符串占位符替换

1.替换单个key

    private final PropertyPlaceholderHelper helper = new PropertyPlaceholderHelper("${", "}");

    @Test
    public void testWithProperties() {
        String text = "foo=${foo}";
        Properties props = new Properties();
        props.setProperty("foo", "bar");

        assertEquals("foo=bar", this.helper.replacePlaceholders(text, props));
    }

2.替换多个key

    @Test
    public void testWithMultipleProperties() {
        String text = "foo=${foo},bar=${bar}";
        Properties props = new Properties();
        props.setProperty("foo", "bar");
        props.setProperty("bar", "baz");

        assertEquals("foo=bar,bar=baz", this.helper.replacePlaceholders(text, props));
    }

3.替换递归属性

    @Test
    public void testRecurseInProperty() {
        String text = "foo=${bar}";
        Properties props = new Properties();
        props.setProperty("bar", "${baz}");
        props.setProperty("baz", "bar");

        assertEquals("foo=bar", this.helper.replacePlaceholders(text, props));
    }

4.StringValueResolver

定义了解析占位符的解析器策略,实际内部是使用了PropertyPlaceholderHelper实现

    private class PlaceholderResolvingStringValueResolver implements StringValueResolver {

        private final PropertyPlaceholderHelper helper;

        private final PlaceholderResolver resolver;

        public PlaceholderResolvingStringValueResolver(Properties props) {
            this.helper = new PropertyPlaceholderHelper(
                    placeholderPrefix, placeholderSuffix, valueSeparator, ignoreUnresolvablePlaceholders);
            this.resolver = new PropertyPlaceholderConfigurerResolver(props);
        }

        @Override
        @Nullable
        public String resolveStringValue(String strVal) throws BeansException {
            String resolved = this.helper.replacePlaceholders(strVal, this.resolver);
            if (trimValues) {
                resolved = resolved.trim();
            }
            return (resolved.equals(nullValue) ? null : resolved);
        }
    }

5. PlaceholderResolver

自定义占位符替换接口,比如以下在replace时则不通过Properties数据源，而是通过自定义的数据源来处理

    @Test
    public void testWithResolver() {
        String text = "foo=${foo}";

        assertEquals("foo=bar",
                this.helper.replacePlaceholders(text, new PropertyPlaceholderHelper.PlaceholderResolver() {
                    @Override
                    public String resolvePlaceholder(String placeholderName) {
                        if ("foo".equals(placeholderName)) {
                            return "bar";
                        }
                        else {
                            return null;
                        }
                    }
                }));
    }