从 Json 到 Object、Java

Question

i have an Array of json objects that looks like this (but has like 30k lines):

{
    "Foglio1": [
        {
            "istat": "1001",
            "cap": "10011"
        },
        {
            "istat": "1002",
            "cap": "10060"
        },
        {
            "istat": "1003",
            "cap": "10070"
        },
        {
            "istat": "1004",
            "cap": "10010"
        },
        {
            "istat": "1006",
            "cap": "10040"
        }
     ]
}

my classes:

public class Test {

    public static void main(String[] args) throws IOException {
        BufferedReader reader=new BufferedReader(new FileReader("italy_cap.json"));
        String cap=reader.readLine();
        Gson g = new Gson();
        Foglio1 p=null;
        while(cap!=null) {
            p = g.fromJson(cap, Foglio1.class);
            
            cap=reader.readLine();
        }
        System.out.println(p);
        
        
    }

}

public class Foglio1 {
    ArrayList <Cap> Foglio1;
}

public class Cap {
    String istat;
    String cap;
    
    public String getIstat() {
        return istat;
    }
    public void setIstat(String istat) {
        this.istat = istat;
    }
    public String getCap() {
        return cap;
    }
    public void setCap(String cap) {
        this.cap = cap;
    }
}

I wanted to read the json and convert it into a java object for parsing it, but i'm not getting how to make it work. the error it's giving me it's:

Exception in thread "main" com.google.gson.JsonSyntaxException: java.io.EOFException: End of input at line 1 column 14 path $.Foglio1[0]
    at com.google.gson.Gson.fromJson(Gson.java:937)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)
    at net.codejava.ws.Test.main(Test.java:21)
Caused by: java.io.EOFException: End of input at line 1 column 14 path $.Foglio1[0]
    at com.google.gson.stream.JsonReader.nextNonWhitespace(JsonReader.java:1401)
    at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:549)
    at com.google.gson.stream.JsonReader.hasNext(JsonReader.java:414)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:81)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
    at `enter code here`com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
    at com.google.gson.Gson.fromJson(Gson.java:927)

As alternative can you give me any ideas of libraries for big json?.

Thank you for the help:)

Answer 1

JSON is not a line-oriented data format, and trying to read it line by line isn't going to work. You can just give the entire file to Gson all at once:

static void main(String[] args) throws IOException {
    try (BufferedReader reader=new BufferedReader(new FileReader("italy_cap.json"))) {
        Gson g = new Gson();
        Foglio1 p = g.fromJson(reader, Foglio1.class);
        System.out.println(p);
    }
}

If your JSON is so big that the objects you create from it don't fit in memory, you can switch to reading it as a stream , but that may require extensive changes to the rest of your program. For example, you may have to change the list within the Foglio1 class to something else, or get rid of the Foglio1 class entirely. Without knowing the rest of your program, it's impossible to say.