JSON se usa comúnmente para intercambiar datos hacia y desde un servidor web. El punto clave aquí es cuando obtenemos los datos del servidor web, luego se devuelven siempre como una string, por lo que debemos tener cuidado en nuestro programa java.
Ilustración:
{"Geeks", "NIT", "Male", "30"}
El analizador JSON devuelve estos datos como un objeto JavaScript, por lo que se convierte en lo siguiente:
const object = JSON.parse({"Geeks", "NIT", "Male", "30"}) ;
Entonces, el mismo trato se calcula con arrays mientras JSON analiza los datos. Escribamos un programa Java que invoque métodos para simplificar la comprensión de cómo se implementa el analizador JSON.
Ejemplo
Java
// Java Program to Implement JSON Parser
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
// Defining constants for json parsers
enum CONSTANTS {
CURLY_OPEN_BRACKETS('{'),
CURLY_CLOSE_BRACKETS('}'),
SQUARE_OPEN_BRACKETS('['),
SQUARE_CLOSE_BRACKETS(']'),
COLON(':'),
COMMA(','),
SPECIAL('|');
private final char constant;
// Constructor
CONSTANTS(char constant) { this.constant = constant; }
// Method
// Overriding exiting toString() method
@Override public String toString()
{
return String.valueOf(constant);
}
}
// Class 1
// To parse json object
class JSONObject {
private final static char specialChar;
private final static char commaChar;
private HashMap<String, String> objects;
static
{
specialChar = String.valueOf(CONSTANTS.SPECIAL)
.toCharArray()[0];
commaChar = String.valueOf(CONSTANTS.COMMA)
.toCharArray()[0];
}
// Constructor if this class
public JSONObject(String arg) { getJSONObjects(arg); }
// Method 1
// Storing json objects as key value pair in hash map
public void getJSONObjects(String arg)
{
objects = new HashMap<String, String>();
if (arg.startsWith(String.valueOf(
CONSTANTS.CURLY_OPEN_BRACKETS))
&& arg.endsWith(String.valueOf(
CONSTANTS.CURLY_CLOSE_BRACKETS))) {
StringBuilder builder = new StringBuilder(arg);
builder.deleteCharAt(0);
builder.deleteCharAt(builder.length() - 1);
builder = replaceCOMMA(builder);
for (String objects : builder.toString().split(
String.valueOf(CONSTANTS.COMMA))) {
String[] objectValue = objects.split(
String.valueOf(CONSTANTS.COLON), 2);
if (objectValue.length == 2)
this.objects.put(
objectValue[0]
.replace("'", "")
.replace("\"", ""),
objectValue[1]
.replace("'", "")
.replace("\"", ""));
}
}
}
// Method 2
public StringBuilder replaceCOMMA(StringBuilder arg)
{
boolean isJsonArray = false;
for (int i = 0; i < arg.length(); i++) {
char a = arg.charAt(i);
if (isJsonArray) {
if (String.valueOf(a).compareTo(
String.valueOf(CONSTANTS.COMMA))
== 0) {
arg.setCharAt(i, specialChar);
}
}
if (String.valueOf(a).compareTo(String.valueOf(
CONSTANTS.SQUARE_OPEN_BRACKETS))
== 0)
isJsonArray = true;
if (String.valueOf(a).compareTo(String.valueOf(
CONSTANTS.SQUARE_CLOSE_BRACKETS))
== 0)
isJsonArray = false;
}
return arg;
}
// Method 3
// Getting json object value by key from hash map
public String getValue(String key)
{
if (objects != null) {
return objects.get(key).replace(specialChar,
commaChar);
}
return null;
}
// Method 4
// Getting json array by key from hash map
public JSONArray getJSONArray(String key)
{
if (objects != null)
return new JSONArray(
objects.get(key).replace('|', ','));
return null;
}
}
// Class 2
// To parse json array
class JSONArray {
private final static char specialChar;
private final static char commaChar;
private ArrayList<String> objects;
static
{
specialChar = String.valueOf(CONSTANTS.SPECIAL)
.toCharArray()[0];
commaChar = String.valueOf(CONSTANTS.COMMA)
.toCharArray()[0];
}
// Constructor of this class
public JSONArray(String arg) { getJSONObjects(arg); }
// Method 1
// Storing json objects in array list
public void getJSONObjects(String arg)
{
objects = new ArrayList<String>();
if (arg.startsWith(String.valueOf(
CONSTANTS.SQUARE_OPEN_BRACKETS))
&& arg.endsWith(String.valueOf(
CONSTANTS.SQUARE_CLOSE_BRACKETS))) {
StringBuilder builder = new StringBuilder(arg);
builder.deleteCharAt(0);
builder.deleteCharAt(builder.length() - 1);
builder = replaceCOMMA(builder);
// Adding all elements
// using addAll() method of Collections class
Collections.addAll(
objects,
builder.toString().split(
String.valueOf(CONSTANTS.COMMA)));
}
}
// Method 2
public StringBuilder replaceCOMMA(StringBuilder arg)
{
boolean isArray = false;
for (int i = 0; i < arg.length(); i++) {
char a = arg.charAt(i);
if (isArray) {
if (String.valueOf(a).compareTo(
String.valueOf(CONSTANTS.COMMA))
== 0) {
arg.setCharAt(i, specialChar);
}
}
if (String.valueOf(a).compareTo(String.valueOf(
CONSTANTS.CURLY_OPEN_BRACKETS))
== 0)
isArray = true;
if (String.valueOf(a).compareTo(String.valueOf(
CONSTANTS.CURLY_CLOSE_BRACKETS))
== 0)
isArray = false;
}
return arg;
}
// Method 3
// Getting json object by index from array list
public String getObject(int index)
{
if (objects != null) {
return objects.get(index).replace(specialChar,
commaChar);
}
return null;
}
// Method 4
// Getting json object from array list
public JSONObject getJSONObject(int index)
{
if (objects != null) {
return new JSONObject(
objects.get(index).replace('|', ','));
}
return null;
}
}
// Class 3
// To parse json string
public class Parser {
// json string with user data
// Custom data been passed as in arguments
private final static String jsonString
= "{'name':'user','id':1234,'marks':[{'english':85,'physics':80,'chemistry':75}]}";
// Main driver method
public static void main(String[] args)
{
// Parse json object for user data
JSONObject user = new JSONObject(jsonString);
// Get json array for user's marks
JSONArray marks = user.getJSONArray("marks");
// Get json object for subject's marks
JSONObject subjects = marks.getJSONObject(0);
// Print and display commands
System.out.println(
String.format("English marks - %s",
subjects.getValue("english")));
System.out.println(
String.format("Physics marks - %s",
subjects.getValue("physics")));
System.out.println(
String.format("Chemistry marks - %s",
subjects.getValue("chemistry")));
}
}
Producción
English marks - 85 Physics marks - 80 Chemistry marks - 75
Publicación traducida automáticamente
Artículo escrito por roshankadam y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA