读取多个JSON行

Question

我得到下面的JSON从网址：

{"bytes": 5043, "name": "a", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"} 
{"bytes": 0, "name": "b", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"} 
{"bytes": 11590, "name": "c", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"} 

我要回字节的每一行。使用杰克逊我试图解析它如下（注：JSON是保存到文件用于测试）：

package JsonRead; 

import java.io.File; 
import java.io.IOException; 

import com.fasterxml.jackson.databind.JsonNode; 
import com.fasterxml.jackson.databind.ObjectMapper; 

public class JacksonTreeModelLogStorage { 
    public static void main(String[] args) { 

     try{ 

      ObjectMapper mapper = new ObjectMapper(); 

      JsonNode root = mapper.readTree(new File("JsonRead/json2.json")); 

      JsonNode logStorageNode = root; 

      for(JsonNode node : logStorageNode){ 
       String bytesUsed = node.path("bytes").asText(); 
       System.out.println("Bytes Used: " + bytesUsed); 
      } 

     } catch(IOException e){ 
       System.out.println("IO Exception " + e); 
     } 
    } 
} 

这将返回以下：

Bytes Used: 
Bytes Used: 
Bytes Used: 
Bytes Used: 

如果我再改我的for循环的以下我可以看到我正在返回json的第一行：

for(JsonNode node : logStorageNode){ 
      String json = node.asText(); 
      System.out.println("json: " + a); 
} 

如何实现json所有行的字节？

Answer 1

谢谢你们。这是一个很大的帮助。

为了适合我的需要，我编辑了一下这个尝试。以下是我最终得到的结果：

ObjectMapper mapper = new ObjectMapper(); 
    try(
      FileReader reader = new FileReader("JsonRead/json2.json"); 
      BufferedReader bufferedReader = new BufferedReader(reader); 
     ) { 
      String currentLine; 
      while((currentLine=bufferedReader.readLine()) != null) { 
       Vault vlt = mapper.readValue(currentLine, Vault.class); 
       System.out.println(vlt.getBytes()); 
      } 
     } 

Answer 2

您发布的内容无效JSON：JSON规范不允许像这样并排多个对象。

如果您遇到这样的文本（它不能被视为JSON），您需要将它分割为一个分隔符，以便每个子字符串都是您将能够解析的有效JSON对象。
在你的情况，看起来换行是一个有效的分隔符，但你应该确保你的JSON对象永远不会包含任何换行符。如果是这样的话，你可以按照如下解析文本：

try(
    FileReader reader = new FileReader("JsonRead/json2.json"); 
    BufferedReader bufferedReader = new BufferedReader(reader); 
) { 
    String currentLine; 
    while((currentLine=bufferedReader.readLine()) != null) { 
     JsonNode logStorageNode = mapper.readTree(currentLine); 
     // [...] carry on with your current code. 
    } 
} 

---

我先假设你正在接受一个数组来代替：

[ 
    {"bytes": 5043, "name": "a", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"}, 
    {"bytes": 0, "name": "b", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"}, 
    {"bytes": 11590, "name": "c", "timestamp": "11-Apr-2017 12:11:51", "ds": "Lab1"} 
] 

在这种情况下，你应该在它的内容循环：

JsonNode root = mapper.readTree(new File("JsonRead/json2.json")); 

if (!root.isArray()) { 
    throw WhateverException("A JSON Array is expected"); 
} 

// a cast to ArrayNode would be possible, but isn't necessary 
// as per the design of jackson's JsonNode 
Iterator<JsonNode> it = root.iterator(); 

while (it.hasNext()) { 
    JsonNode logStorageNode = it.next(); 

    // [...] carry on with your current code. 
}