实现 JSON 解析器的 Java 程序
原文:https://www . geesforgeks . org/Java-program-to-implement-a-JSON-parser/
JSON 通常用于在网络服务器之间来回交换数据。这里的关键点是，当我们从 web 服务器获取数据时，它总是作为一个字符串返回，所以我们在 java 程序中需要小心吗？
插图:
{"Geeks", "NIT", "Male", "30"}
这个数据由 JSON 解析器作为一个 JavaScript 对象返回，因此它变成如下所示:
const object = JSON.parse({"Geeks", "NIT", "Male", "30"}) ;
在 JSON 解析数据时，对数组进行同样的处理。让我们编写一个 java 程序调用方法，以便更容易理解 JSON 解析器是如何实现的。
例
Java 语言(一种计算机语言，尤用于创建网站)
// 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")));
}
}
Output
English marks - 85
Physics marks - 80
Chemistry marks - 75
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