返回Java中递归函数的值

Question

我正试图从while循环中提取一个值。在输出中，我可以捕获Else语句中的值，但当它在控制台日志中时，我无法从主语句返回它。我希望能够返回"；103〃；当我调用CCD_ 2函数时。

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Iterator;
import org.json.JSONArray;
import org.json.JSONObject;
import org.json.XML;
public class Tesst {

static String line = "", str = "";

public static void main(String[] args) throws Exception {
String filepath = "C:/Users/Navi/Downloads/sample.xml";

BufferedReader br = new BufferedReader(new FileReader(filepath));
while ((line = br.readLine()) != null) {
str += line;
}

br.close();
JSONObject jsondata = XML.toJSONObject(str);

System.out.println("From main: " + getValueFromKey(jsondata, "routing_bic"));
}
private static Integer getValueFromKey(JSONObject json, String key) {
boolean exists = json.has(key);
Iterator<?> keys;
String nextKeys;
Integer foundKey = 0;
if(!exists) {
keys = json.keys();
while (keys.hasNext()) {
// Store next Key in nextKeys
nextKeys = (String)keys.next();

try {
// Check if the given Key is a JSON Object
if(json.get(nextKeys) instanceof JSONObject) {
// If Key does not exist
if(!exists) {
// Recursive function call
getValueFromKey(json.getJSONObject(nextKeys), key);
}
} else if (json.get(nextKeys) instanceof JSONArray) {
JSONArray jsonArray = json.getJSONArray(nextKeys);
for(int i = 0; i < jsonArray.length(); i++) {
String jsonArrayString = jsonArray.get(i).toString();
JSONObject innerJsonObject = new JSONObject(jsonArrayString);

// Recursive function call
if(!exists) {
getValueFromKey(innerJsonObject.getJSONObject(nextKeys), key);
}
}
}
} catch (Exception e) {
System.out.println(e);
}
}
} else {
// If key exists, print value
foundKey += parseObject(json, key);
System.out.println("From loop: " + foundKey);
return foundKey;
}
//      System.out.println("Found Key = " + foundKey);
return 1; // Return 1 when key not found
}

private static Integer parseObject(JSONObject json, String key) {
System.out.println("From parseObject = " + json.get(key));
return (Integer) json.get(key);
}

}

示例XML

<Test>
<BIBRq>
<UserId>123</UserId>
<CIFNo>123</CIFNo>
<CompanyId>asd</CompanyId>
<LegalId>123</LegalId>
<LegalIdType>ABC</LegalIdType>
<LegalIdCountry>ABC</LegalIdCountry>
</BIBRq>
<SubSvcRq>
<SubSvc>
<SubSvcRqHeader>
<SvcCode>ABCD</SvcCode>
<SubSvcSeq>1</SubSvcSeq>
<TxnRef>12345</TxnRef>
<ClientUserID/>
</SubSvcRqHeader>
<SubSvcRqDetail>
<ft_tnx_record>
<additional_field>
<account_details>
<routing_bic>103</routing_bic>
</account_details>
</additional_field>
</ft_tnx_record>
</SubSvcRqDetail>
</SubSvc>
</SubSvcRq>
</Test>

输出：

来自parseObject=103

来自环路：103

来自主：1

Answer 1

您的代码中有两个错误。

1. 我注意到您递归地调用函数getValueFromKey。如果不为变量foundKey分配递归调用的返回值，这将永远不会起作用
   所以，只需更改以下中的每个递归调用：

   foundKey=getValueFromKey(…，key(；

2. 此外，最后一条语句return 1是错误的，因为它将覆盖后续递归调用返回的任何可能值。因此，在替换中，您必须始终返回foundKey变量
   

我稍微修改了您的代码，并用您的示例文件对其进行了测试，它运行良好。与您的不同，我还用try-with-resourcece块封装了BufferedReader，我一直更喜欢它而不是简单的try-catch，因为它保证它会为您关闭流，即使在出现异常的情况下也是如此

这是代码：

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.Iterator;
import org.json.JSONArray;
import org.json.JSONObject;
import org.json.XML;
public class Test {

static String line = "", str = "";

public static void main(String[] args) throws Exception {
String filepath = "C:\Users\marco\Downloads\sample.xml";

try ( BufferedReader br = new BufferedReader(new FileReader(filepath)); ) {
while ((line = br.readLine()) != null) {
str += line;
}
}
JSONObject jsondata = XML.toJSONObject(str);

System.out.println("From main: " + getValueFromKey(jsondata, "routing_bic"));
}
private static Integer getValueFromKey(JSONObject json, String key) {
boolean exists = json.has(key);
Iterator<?> keys;
String nextKeys;
Integer foundKey = 0;
if(!exists) {
keys = json.keys();
while (keys.hasNext()) {
// Store next Key in nextKeys
nextKeys = (String)keys.next();

try {
// Check if the given Key is a JSON Object
if(json.get(nextKeys) instanceof JSONObject) {
// If Key does not exist
if(!exists) {
// Recursive function call
foundKey = getValueFromKey(json.getJSONObject(nextKeys), key);
}
} else if (json.get(nextKeys) instanceof JSONArray) {
JSONArray jsonArray = json.getJSONArray(nextKeys);
for(int i = 0; i < jsonArray.length(); i++) {
String jsonArrayString = jsonArray.get(i).toString();
JSONObject innerJsonObject = new JSONObject(jsonArrayString);

// Recursive function call
if(!exists) {
foundKey = getValueFromKey(innerJsonObject.getJSONObject(nextKeys), key);
}
}
}
} catch (Exception e) {
System.out.println(e);
}
}
} else {
// If key exists, print value
foundKey += parseObject(json, key);
System.out.println("From loop: " + foundKey);
}
//      System.out.println("Found Key = " + foundKey);
return foundKey; // Return 1 when key not found
}

private static Integer parseObject(JSONObject json, String key) {
System.out.println("From parseObject = " + json.get(key));
return (Integer) json.get(key);
}

}

这是输出：

From parseObject = 103
From loop: 103
From main: 103