Java实现JSON解析

测试

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public class Main {

public static void main(String[] args) throws Exception {
String text =
"{\n" +
" \"transformRequest\":\n" +
" {},\n" +
" \"transformResponse\":\n" +
" {},\n" +
" \"timeout\": 30000,\n" +
" \"xsrfHeaderName\": [\"X-XSRF-TOKEN\",\"X-XSRF-TOKEN2\",\"X-XSRF-TOKEN3\"],\n" +
" \"maxContentLength\": -1,\n" +
" \"headers\":\n" +
" {\n" +
" \"Accept\": \"application/json, text/plain, */*\",\n" +
" \"Content-Type\": \"application/json;charset=UTF-8\"\n" +
" },\n" +
" \"data\": \"{\\\"page\\\":1,\\\"limit\\\":10}\"\n" +
"}";

System.out.println(JSONUtils.formatText(text));
System.out.println("===================");
System.out.println(JSON.toJSONString(JSONUtils.parseText(text), true));
}
}

实现

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import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class JSONUtils {

public static Map<String, Object> parseObjectText(String text) throws Exception {
Object o = parseText(text);
if (!(o instanceof Map)) {
throw new Exception();
}
return (Map<String, Object>) o;
}

public static List<Object> parseArrayText(String text) throws Exception {
Object o = parseText(text);
if (!(o instanceof List)) {
throw new Exception();
}
return (List<Object>) o;
}

public static Object parseText(String text) throws Exception {
return parseTokens(parseTextToTokens(text), 0).data;
}

public static String formatText(String text) throws Exception {
return formatTokens(parseTextToTokens(text));
}

private static Token getFirstToken(String text, TokenType type) {
Matcher matcher = type.pattern.matcher(text);
if (!matcher.find()) {
return null;
}
return new Token(type, matcher.group(0));
}

private static String transString(String text) {
StringBuilder val = new StringBuilder();
for (int i = 1; i < text.length() - 1; i++) {
if (text.charAt(i) != '\\') {
val.append(text.charAt(i));
} else {
switch (text.charAt(i + 1)) {
case 'n':
val.append('\n');
break;
case 't':
val.append('\t');
break;
default:
val.append(text.charAt(i + 1));
break;
}
i++;
}
}
return val.toString();
}

private static TokensParseResult parseTokens(List<Token> tokens, int index) throws Exception {
switch (tokens.get(index).type) {
case OBJECT_OPEN: {
index++;
Map<String, Object> data = new HashMap<>();
while (tokens.get(index).type != TokenType.OBJECT_CLOSE) {
if (tokens.get(index).type == TokenType.STRING && tokens.get(index + 1).type == TokenType.COLON) {
TokensParseResult item = parseTokens(tokens, index + 2);
data.put(transString(tokens.get(index).value), item.data);
index = item.nextIndex;
if (tokens.get(index).type == TokenType.SPLIT) {
index++;
}
} else {
throw new Exception();
}
}
return new TokensParseResult(data, index + 1);
}
case ARRAY_OPEN: {
index++;
List<Object> data = new ArrayList<>();
while (tokens.get(index).type != TokenType.ARRAY_CLOSE) {
TokensParseResult item = parseTokens(tokens, index);
data.add(item.data);
index = item.nextIndex;
if (tokens.get(index).type == TokenType.SPLIT) {
index++;
}
}
return new TokensParseResult(data, index + 1);

}
case STRING:
return new TokensParseResult(transString(tokens.get(index).value), index + 1);
case NUMBER:
return new TokensParseResult(Double.parseDouble(tokens.get(index).value), index + 1);
case BOOLEAN:
return new TokensParseResult(Boolean.parseBoolean(tokens.get(index).value), index + 1);
case NULL:
return new TokensParseResult(null, index + 1);
default:
throw new Exception();
}
}

private static String enter(int depth) {
StringBuilder val = new StringBuilder("\n");
for (int i = 0; i < depth; i++) {
val.append(" ");
}
return val.toString();
}

private static String formatTokens(List<Token> tokens) {
StringBuilder format = new StringBuilder();
int depth = 0;
for (Token token : tokens) {
if (token.type == TokenType.OBJECT_CLOSE || token.type == TokenType.ARRAY_CLOSE) {
format.append(enter(--depth));
}
format.append(token.value);
if (token.type == TokenType.OBJECT_OPEN || token.type == TokenType.ARRAY_OPEN) {
format.append(enter(++depth));
}
if (token.type == TokenType.SPLIT) {
format.append(enter(depth));
}
}
return format.toString();
}

private static List<Token> parseTextToTokens(String text) throws Exception {
List<Token> tokens = new ArrayList<>();
while (!text.isEmpty()) {
Token token = null;
for (TokenType type : TokenType.values()) {
token = getFirstToken(text, type);
if (token != null) {
break;
}
}
if (token == null) {
throw new Exception();
}
text = text.substring(token.value.length());
if (token.type == TokenType.SPACE) {
continue;
}
tokens.add(token);
}
return tokens;
}

private static class Token {
private TokenType type;
private String value;

private Token(TokenType type, String value) {
this.type = type;
this.value = value;
}
}

private static class TokensParseResult {
private Object data;
private int nextIndex;

TokensParseResult(Object data, int nextIndex) {
this.data = data;
this.nextIndex = nextIndex;
}
}

private enum TokenType {
STRING("^(\"([^\"\\\\]|\\\\.)*\")"),
NUMBER("^(-?\\d+(\\.\\d+)?)"),
BOOLEAN("^(true|false)"),
NULL("^(null)"),
OBJECT_OPEN("^(\\{)"),
OBJECT_CLOSE("^(\\})"),
ARRAY_OPEN("^(\\[)"),
ARRAY_CLOSE("^(\\])"),
COLON("^(\\:)"),
SPLIT("^(\\,)"),
SPACE("^([\\s\\r\\n]+)");

private Pattern pattern;

TokenType(String reg) {
this.pattern = Pattern.compile(reg);
}
}
}
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