高效更新 Java 中 JSON 数组中的对象：使用 Josson 库实现

本文旨在介绍如何高效地更新 Java 中 JSON 数组内的对象。当需要根据特定匹配键（如userid和scripcode）将一个 JSON 数组（websocketjsonArray）中的数据更新到另一个 JSON 数组（http）中的对应对象时，传统嵌套循环方法效率低下且易出错。我们将重点探讨如何利用 Josson 库提供的强大查询和连接功能，以简洁、声明式的方式实现这一复杂的数据合并与更新操作，显著提升代码的可读性和执行效率。

1. 问题背景与传统方法的局限性

在数据处理场景中，我们经常会遇到需要同步或合并来自不同数据源的 json 数据。例如，给定两个 jsonarray：http 和 websocketjsonarray，它们都包含一系列 jsonobject。我们的目标是，如果 websocketjsonarray 中的某个对象与 http 数组中的某个对象在 userid 和 scripcode 字段上完全匹配，则将 websocketjsonarray 中该对象的特定字段（如 bfqty）的值更新到 http 数组中对应的对象上。

传统的实现方式通常涉及嵌套循环：遍历 websocketjsonArray，在内部循环遍历 http 数组，然后使用 if 条件判断 userid 和 scripcode 是否匹配。一旦匹配成功，就手动从源对象获取值并更新目标对象。这种方法虽然直观，但存在以下局限性：

效率低下：对于大型 JSON 数组，嵌套循环的时间复杂度为 O(N*M)，其中 N 和 M 分别是两个数组的长度，这会导致性能瓶颈。代码冗余：手动的数据查找、比较和更新逻辑会使代码变得冗长且难以维护。易出错：在复杂的条件判断和数据类型转换中，容易引入逻辑错误。

2. 引入 Josson 库：高效的 JSON 数据操作利器

为了解决上述问题，我们可以利用 Josson 和 Jossons 库。Josson 是一个强大的 Java JSON 处理器，它提供了一种类似 SQL 的查询语言来操作 JSON 数据，包括数据选择、过滤、转换和连接等。Jossons 则是 Josson 的一个扩展，支持多数据集操作，非常适合我们当前的需求。

2.1 添加 Josson 依赖

在使用 Josson 之前，需要将其添加到项目的 pom.xml（Maven）或 build.gradle（Gradle）文件中。

Maven:

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    com.github.octomix.josson    josson    1.4.1 

Gradle:

implementation 'com.github.octomix.josson:josson:1.4.1' // 请使用最新版本

2.2 数据准备与数据集注册

首先，我们需要将原始的 JSON 字符串解析成 Josson 对象，并通过 Jossons 注册为命名数据集。这使得我们可以在查询中通过名称引用它们。

import com.fasterxml.jackson.databind.JsonNode;import com.octomix.josson.Josson;import com.octomix.josson.Jossons;public class JsonArrayUpdater {    public static void main(String[] args) {        try {            // 原始 HTTP 数据            String httpJsonString = "[{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38021","securitytype":"OPT","strikeprice":17700,"opttype":"PE","bfqty":-1500,"bfrate":122.35,"bfamt":18352.5,"buyqty":0,"sellqty":0,"netqty":0,"cfqty":-150,"cfamt":18352.5,"ltp":0,"grossmtm":0,"brokerageamt":0,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1},{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38026","securitytype":"OPT","strikeprice":17800,"opttype":"PE","bfqty":0,"bfrate":0,"bfamt":0,"buyqty":10800,"sellqty":15000,"netqty":-4200,"cfqty":-4200,"cfamt":590729.9999999998,"ltp":0,"grossmtm":0,"brokerageamt":3400.2888479999992,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":11},{"userid":"CNC01","groupname":"abhishek","segment":"Cosmic","accountcode":"APP","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"40034","securitytype":"OPT","strikeprice":1200,"opttype":"PE","bfqty":12,"bfrate":2,"bfamt":0,"buyqty":100,"sellqty":121,"netqty":200,"cfqty":11,"cfamt":78,"ltp":9,"grossmtm":0,"brokerageamt":12222,"netmtm":45,"currency":"INR","usdrate":2,"clientsharing":0,"broksharing":0,"comsharing":0,"multiplier":99}]";            // WebSocket 更新数据            String websocketJsonString = "[{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38021","securitytype":"OPT","strikeprice":17700,"opttype":"PE","bfqty":20,"bfrate":122.35,"bfamt":18352.5,"buyqty":0,"sellqty":0,"netqty":0,"cfqty":-150,"cfamt":18352.5,"ltp":0,"grossmtm":0,"brokerageamt":0,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1},{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38026","securitytype":"OPT","strikeprice":17800,"opttype":"PE","bfqty":30,"bfrate":0,"bfamt":0,"buyqty":10800,"sellqty":15000,"netqty":-4200,"cfqty":-4200,"cfamt":590729.9999999998,"ltp":0,"grossmtm":0,"brokerageamt":3400.2888479999992,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1}]]";            Jossons jossons = new Jossons();            jossons.putDataset("http", Josson.fromJsonString(httpJsonString));            jossons.putDataset("websocket", Josson.fromJsonString(websocketJsonString));            System.out.println("原始 http 数据:n" + jossons.getDataset("http").toPrettyString());            System.out.println("原始 websocket 数据:n" + jossons.getDataset("websocket").toPrettyString());            // ... 后续执行查询        } catch (Exception e) {            e.printStackTrace();        }    }}

2.3 执行数据合并与更新（左连接操作）

Josson 提供了强大的查询语法来实现数据连接和更新。在本例中，我们将使用左连接（<=<）操作符来将 websocket 数据集中的匹配字段更新到 http 数据集中。

核心查询语句是：http{userid,scripcode} <=map(userid,scripcode,bfqty){userid,scripcode}

让我们分解这个查询：

http{userid,scripcode}: 指定左侧数据集为 http，并且定义用于匹配的键是 userid 和 scripcode。<=map(userid,scripcode,bfqty){userid,scripcode}:websocket: 指定右侧数据集为 websocket。->map(userid,scripcode,bfqty): 这是一个映射（map）操作，它从 websocket 数据集中为每个对象选择 userid, scripcode, bfqty 这三个字段。这意味着只有这些字段会被考虑用于更新。{userid,scripcode}: 指定右侧数据集用于匹配的键也是 userid 和 scripcode。

当查询执行时，Josson 会根据 userid 和 scripcode 将 http 中的对象与 websocket 中映射后的对象进行匹配。如果找到匹配，websocket 中 map 操作选取的字段（即 bfqty）的值将覆盖 http 中对应对象的 bfqty 值。

完整代码示例：

import com.fasterxml.jackson.databind.JsonNode;import com.octomix.josson.Josson;import com.octomix.josson.Jossons;import org.json.JSONArray; // 引入 org.json.JSONArray 以匹配原始问题中的数据结构public class JsonArrayUpdateExample {    // 假设这是您的Activity或主类    public static void main(String[] args) {        try {            // 原始 HTTP 数据，使用 org.json.JSONArray 兼容原始问题            JSONArray http = new JSONArray("[{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38021","securitytype":"OPT","strikeprice":17700,"opttype":"PE","bfqty":-1500,"bfrate":122.35,"bfamt":18352.5,"buyqty":0,"sellqty":0,"netqty":0,"cfqty":-150,"cfamt":18352.5,"ltp":0,"grossmtm":0,"brokerageamt":0,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1},{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38026","securitytype":"OPT","strikeprice":17800,"opttype":"PE","bfqty":0,"bfrate":0,"bfamt":0,"buyqty":10800,"sellqty":15000,"netqty":-4200,"cfqty":-4200,"cfamt":590729.9999999998,"ltp":0,"grossmtm":0,"brokerageamt":3400.2888479999992,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":11},{"userid":"CNC01","groupname":"abhishek","segment":"Cosmic","accountcode":"APP","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"40034","securitytype":"OPT","strikeprice":1200,"opttype":"PE","bfqty":12,"bfrate":2,"bfamt":0,"buyqty":100,"sellqty":121,"netqty":200,"cfqty":11,"cfamt":78,"ltp":9,"grossmtm":0,"brokerageamt":12222,"netmtm":45,"currency":"INR","usdrate":2,"clientsharing":0,"broksharing":0,"comsharing":0,"multiplier":99}]");            // WebSocket 更新数据，使用 org.json.JSONArray 兼容原始问题            JSONArray websocketjsonArray = new JSONArray("[{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38021","securitytype":"OPT","strikeprice":17700,"opttype":"PE","bfqty":20,"bfrate":122.35,"bfamt":18352.5,"buyqty":0,"sellqty":0,"netqty":0,"cfqty":-150,"cfamt":18352.5,"ltp":0,"grossmtm":0,"brokerageamt":0,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1},{"userid":"CNRM04","groupname":"Rohit","segment":"CosPROFIN","accountcode":"OWN","symbol":"NIFTY","exchange":"NSEFO","expirydate":"03NOV2022","scripcode":"38026","securitytype":"OPT","strikeprice":17800,"opttype":"PE","bfqty":30,"bfrate":0,"bfamt":0,"buyqty":10800,"sellqty":15000,"netqty":-4200,"cfqty":-4200,"cfamt":590729.9999999998,"ltp":0,"grossmtm":0,"brokerageamt":3400.2888479999992,"netmtm":0,"currency":"INR","usdrate":1,"clientsharing":0,"broksharing":0,"comsharing":100,"multiplier":1}]]");            // 初始化 Jossons 实例            Jossons jossons = new Jossons();            // 将 JSONArray 转换为 Josson 对象并注册为数据集            // 注意：Josson.fromJsonString 接受 JSON 字符串，而不是 org.json.JSONArray 对象            jossons.putDataset("http", Josson.fromJsonString(http.toString()));            jossons.putDataset("websocket", Josson.fromJsonString(websocketjsonArray.toString()));            System.out.println("--- 原始数据 ---");            System.out.println("http:n" + jossons.getDataset("http").toPrettyString());            System.out.println("websocket:n" + jossons.getDataset("websocket").toPrettyString());            // 执行左连接更新操作            JsonNode updatedHttpNode = jossons.evaluateQuery(                    "http{userid,scripcode} <=map(userid,scripcode,bfqty){userid,scripcode}");            System.out.println("n--- 更新后的数据 ---");            System.out.println(updatedHttpNode.toPrettyString());        } catch (Exception e) {            e.printStackTrace();        }    }}

2.4 预期输出

运行上述代码，您将看到 http 数组中 bfqty 字段的值根据 websocket 数组中的匹配项进行了更新：

[ {  "userid" : "CNRM04",  "groupname" : "Rohit",  "segment" : "CosPROFIN",  "accountcode" : "OWN",  "symbol" : "NIFTY",  "exchange" : "NSEFO",  "expirydate" : "03NOV2022",  "scripcode" : "38021",  "securitytype" : "OPT",  "strikeprice" : 17700,  "opttype" : "PE",  "bfqty" : 20,  "bfrate" : 122.35,  "bfamt" : 18352.5,  "buyqty" : 0,  "sellqty" : 0,  "netqty" : 0,  "cfqty" : -150,  "cfamt" : 18352.5,  "ltp" : 0,  "grossmtm" : 0,  "brokerageamt" : 0,  "netmtm" : 0,  "currency" : "INR",  "usdrate" : 1,  "clientsharing" : 0,  "broksharing" : 0,  "comsharing" : 100,  "multiplier" : 1}, {  "userid" : "CNRM04",  "groupname" : "Rohit",  "segment" : "CosPROFIN",  "accountcode" : "OWN",  "symbol" : "NIFTY",  "exchange" : "NSEFO",  "expirydate" : "03NOV2022",  "scripcode" : "38026",  "securitytype" : "OPT",  "strikeprice" : 17800,  "opttype" : "PE",  "bfqty" : 30,  "bfrate" : 0,  "bfamt" : 0,  "buyqty" : 10800,  "sellqty" : 15000,  "netqty" : -4200,  "cfqty" : -4200,  "cfamt" : 590729.9999999998,  "ltp" : 0,  "grossmtm" : 0,  "brokerageamt" : 3400.2888479999992,  "netmtm" : 0,  "currency" : "

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