解析超大JSON文件

1、需求

最近项目中需要将一个一个大于800M的JSON文件导出到Excel中，试过普通的按行读取文件和JSONReader流读取文件，由于JSON文件实在过于庞大，导致OOM问题

2、解决方案

每个json数组中包含的json对象太多，导致用流和按行读取时加载到内存会导致内存溢出。.

最终采用了JsonToken的解决方案。

package com.godfrey.poi.util;


import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.MappingJsonFactory;

import java.io.File;

/**
 * @author godfrey
 * @since 2021-12-05
 */
public class ParseJsonUtil {
    public static void main(String[] args) throws Exception {
        JsonFactory f = new MappingJsonFactory();
        JsonParser jp = f.createJsonParser(new File("F:/FeaturesToJSON.json"));
        JsonToken current;
        current = jp.nextToken();
        if (current != JsonToken.START_OBJECT) {
            System.out.println("Error: root should be object: quiting.");
            return;
        }
        while (jp.nextToken() != JsonToken.END_OBJECT) {
            String fieldName = jp.getCurrentName();
            // move from field name to field value
            current = jp.nextToken();
            if ("features".equals(fieldName)) {
                if (current == JsonToken.START_ARRAY) {
                    // For each of the records in the array
                    while (jp.nextToken() != JsonToken.END_ARRAY) {
                        // read the record into a tree model,
                        // this moves the parsing position to the end of it
                        JsonNode node = jp.readValueAsTree();
                        // And now we have random access to everything in the object
                        System.out.println("field1: " + node.get("field1").asText());
                        System.out.println("field2: " + node.get("field2").asText());
                    }
                } else {
                    System.out.println("Error: records should be an array: skipping.");
                    jp.skipChildren();
                }
            } else {
                System.out.println("Unprocessed property: " + fieldName);
                jp.skipChildren();
            }
        }
    }
}

代码中使用流和树模型解析的组合读取此文件。 每个单独的记录都以树形结构读取，但文件永远不会完整地读入内存，因此JVM内存不会爆炸。最终解决了读取超大文件的问题。