看懂 HTTP 请求、JSON 与 API 错误

import java.util.*;
public class Main {
    static List<String> frames(List<String> chunks){
        List<String> out=new ArrayList<>(); Deque<Character> stack=new ArrayDeque<>();
        StringBuilder b=new StringBuilder(); boolean in=false,escape=false;
        for(String chunk:chunks)for(char c:chunk.toCharArray()){
            if(stack.isEmpty()){
                if(Character.isWhitespace(c))continue;
                if(c!='{')throw new IllegalArgumentException("object expected");
            }
            b.append(c);
            if(in){
                if(escape)escape=false; // 转义后的引号不能结束字符串。
                else if(c==92)escape=true; // 92 是反斜线字符。
                else if(c=='"')in=false;
                continue;
            }
            if(c=='"'){in=true;continue;}
            if(c=='{'||c=='[')stack.push(c);
            else if(c=='}'||c==']'){
                if(stack.isEmpty()||stack.pop()!=(c=='}'?'{':'['))throw new IllegalArgumentException("mismatch");
                if(stack.isEmpty()){out.add(b.toString());b.setLength(0);}
            }
        }
        if(in||!stack.isEmpty())throw new IllegalArgumentException("truncated");
        return out;
    }
    static void check(List<String> expected,List<String> actual){if(!expected.equals(actual))throw new AssertionError(actual);}
    static void rejects(String text){try{frames(List.of(text));throw new AssertionError();}catch(IllegalArgumentException expected){}}
    public static void main(String[] args){
        check(List.of("{\"a\":1}","{\"b\":2}"),frames(List.of("{\"a\":","1}{\"b\":2}")));
        check(List.of("{\"x\":\"}\"}"),frames(List.of("{\"x\":\"}","\"}")));// 字符串中的括号。
        check(List.of("{\"x\":\"a\\\"b\"}"),frames(List.of("{\"x\":\"a\\","\"b\"}")));
        check(List.of(),frames(List.of("  ","\n")));
        rejects("{\"a\":[}"); rejects("{\"a\":1");
        check(List.of("{bad}"),frames(List.of("{bad}")));// 分帧器不冒充语法解析器。
        System.out.println("PASS 7 tests");
    }
}