Question

我目前正在尝试优化java中的json解析是不是可以从头到尾解析一个Json？

我使用faster-xml / jackson-core（2.2.3）库来解析以下json对象这些实际上是按年份分组的嵌套对象，然后是月份。请参阅下面的示例，有些年份只有几个月相关，所以其他几个省略。 json对象是我在Java中解析的网站的一部分。假设我只想解析当前年份（2014年）下降的最新5个订单。问题：json对象是按升序排列的，所以要获得最新的5个entr，我必须从头到尾通过整个json对象。

有没有办法反过来做？或者重新加载json对象？其他想法可以解决这个问题吗？

  var calendarGroupYearMonth = $.parseJSON('{"2000":{"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2001":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2002":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2003":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2004":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2005":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2006":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2007":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2008":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2009":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2010":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2011":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2012":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2013":{"1":1,"2":1,"3":1,"4":1,"5":1,"6":1,"7":1,"8":1,"9":1,"10":1,"11":1,"12":1},"2014":{"1":1,"2":1,"3":1}}');

我不希望它作为对象结构，所以我通过令牌解析它令牌这是我的json解析代码，工作正常。

    JsonParser parser = jf.createParser(jsonSTring);
    JsonToken currentToken = parser.nextToken();
            String month = "";
            String year = "";
            final int YEAR_LENGTH = 4;

            while (parser.hasCurrentToken()) {

                if (currentToken == JsonToken.FIELD_NAME) {
                    String text = parser.getText();
                    if (text.length() == YEAR_LENGTH) {
                        year = text;

                    } else {
                        month = text;
                    }
//Do some stuff with the year and month
                }
    currentToken = parser.nextToken();

Answer 1

您只需使用@JsonAnySetter注释即可。您的POJO课程应如下所示：

class Pojo {

    private static final int MAX_SIZE = 5;

    private TreeMap<Integer, Map<String, String>> yearsMap = new TreeMap<>(new Comparator<Integer>() {
        @Override
        public int compare(Integer value1, Integer value2) {
            return value2.compareTo(value1);
        };
    });

    @JsonAnySetter
    public void setMonthFromLastYear(String year, Map<String, String> value) {
        Integer currentYear = Integer.valueOf(year);
        if (yearsMap.size() <= MAX_SIZE) {
            yearsMap.put(currentYear, value);
        } else if (currentYear > yearsMap.lastKey()) {
            yearsMap.remove(yearsMap.lastKey());
            yearsMap.put(currentYear, value);
        }
    }

    public Map<String, String> getValuesForYear(int year) {
        return yearsMap.get(year);
    }

    @Override
    public String toString() {
        return String.valueOf(yearsMap);
    }
}

简单用法：

ObjectMapper om = new ObjectMapper();
Pojo demoClass = om.readValue(json, Pojo.class);
System.out.println(demoClass);
System.out.println("Year 2014: " + demoClass.getValuesForYear(2014));

以上程序打印：

{2014={1=1, 2=1, 3=1}, 2013={1=1, 2=1, 3=1, 4=1, 5=1, 6=1, 7=1, 8=1, 9=1, 10=1, 11=1, 12=1}, 2012={1=1, 2=1, 3=1, 4=1, 5=1, 6=1, 7=1, 8=1, 9=1, 10=1, 11=1, 12=1}, 2011={1=1, 2=1, 3=1, 4=1, 5=1, 6=1, 7=1, 8=1, 9=1, 10=1, 11=1, 12=1}, 2010={1=1, 2=1, 3=1, 4=1, 5=1, 6=1, 7=1, 8=1, 9=1, 10=1, 11=1, 12=1}, 2009={1=1, 2=1, 3=1, 4=1, 5=1, 6=1, 7=1, 8=1, 9=1, 10=1, 11=1, 12=1}}
Year 2014: {1=1, 2=1, 3=1}

从终点到开始解析json

1 个答案: