java校验字符串是否为json格式
觉得挺好玩的一个问题，如何校验字符串是否为标准的json格式，刚开始的回答是jsonObject或者jsonArray转换一下，如果可以转换，说明为json字符串，如果不能就抛出异常，捕获异常。
但是不让用这种方式。于是查资料从字符串和字符下手。
package com.lsm.util;
import java.text.CharacterIterator;
import java.text.StringCharacterIterator;
/**
* 用于校验一个字符串是否是合法的JSON格式
* @author liShuMin
*
*/
public class JsonValidator {
private CharacterIterator it;
private char c;
private int col;
public JsonValidator(){
}
/**
* 验证一个字符串是否是合法的JSON串
*
* @param input 要验证的字符串
* @return true-合法 ，false-非法
*/
public boolean validate(String input) {
input = input.trim();
boolean ret = valid(input);
return ret;
}
private boolean valid(String input) {
if ("".equals(input)) return true;
boolean ret = true;
it = new StringCharacterIterator(input);
c = it.first();
col = 1;
if (!value()) {
ret = error("value", 1);
} else {
skipWhiteSpace();
if (c != CharacterIterator.DONE) {
ret = error("end", col);
}
}
return ret;
}
private boolean value() {
return literal("true") || literal("false") || literal("null") || string() || number() || object() || array();
}
private boolean literal(String text) {
CharacterIterator ci = new StringCharacterIterator(text);
char t = ci.first();
if (c != t) return false;
int start = col;
boolean ret = true;
for (t = ci.next(); t != CharacterIterator.DONE; t = ci.next()) {
if (t != nextCharacter()) {
ret = false;
break;
}
}
nextCharacter();
if (!ret) error("literal " + text, start);
return ret;
}
private boolean array() {
return aggregate('[', ']', false);
}
private boolean object() {
return aggregate('{', '}', true);
}
private boolean aggregate(char entryCharacter, char exitCharacter, boolean prefix) {
if (c != entryCharacter) return false;
nextCharacter();
skipWhiteSpace();
if (c == exitCharacter) {
nextCharacter();
return true;
}
for (;;) {
if (prefix) {
int start = col;
if (!string()) return error("string", start);
skipWhiteSpace();
if (c != ':') return error("colon", col);
nextCharacter();
skipWhiteSpace();
}
if (value()) {
skipWhiteSpace();
if (c == ',') {
nextCharacter();
} else if (c == exitCharacter) {
break;
} else {
return error("comma or " + exitCharacter, col);
}
} else {
return error("value", col);
}
skipWhiteSpace();
}
nextCharacter();
return true;
}
private boolean number() {
if (!Character.isDigit(c) && c != '-') return false;
int start = col;
if (c == '-') nextCharacter();
if (c == '0') {
nextCharacter();
} else if (Character.isDigit(c)) {
while (Character.isDigit(c))
nextCharacter();
} else {
return error("number", start);
}
if (c == '.') {
nextCharacter();
if (Character.isDigit(c)) {
while (Character.isDigit(c))
nextCharacter();
} else {
return error("number", start);
}
}
if (c == 'e' || c == 'E') {
nextCharacter();
if (c == '+' || c == '-') {
nextCharacter();
}
if (Character.isDigit(c)) {
while (Character.isDigit(c))
nextCharacter();
} else {
return error("number", start);
}
}
return true;
}
private boolean string() {
if (c != '"') return false;
int start = col;
boolean escaped = false;
for (nextCharacter(); c != CharacterIterator.DONE; nextCharacter()) {
if (!escaped && c == '\') {
escaped = true;
} else if (escaped) {
if (!escape()) {
return false;
}
escaped = false;
} else if (c == '"') {
nextCharacter();
return true;
}
}
return error("quoted string", start);
}
private boolean escape() {
int start = col - 1;
if (" \"/bfnrtu".indexOf(c) < 0) {
return error("escape sequence \",\\,\/,\b,\f,\n,\r,\t or \uxxxx ", start);
}
if (c == 'u') {
if (!ishex(nextCharacter()) || !ishex(nextCharacter()) || !ishex(nextCharacter())
|| !ishex(nextCharacter())) {
return error("unicode escape sequence \uxxxx ", start);
}
}
return true;
}
private boolean ishex(char d) {
return "0123456789abcdefABCDEF".indexOf(c) >= 0;
}
private char nextCharacter() {
c = it.next();
++col;
return c;
}
private void skipWhiteSpace() {
while (Character.isWhitespace(c)) {
nextCharacter();
}
}
private boolean error(String type, int col) {
System.out.printf("type: %s, col: %s%s", type, col, System.getProperty("line.separator"));
return false;
}
public static void main(String[] args){
//String jsonStr = "{"website":"oschina.net"}";
String jsonStr = "{"
+ " "ccobjtypeid": "1001","
+ " "fromuser": "李四","
+ " "touser": "张三","
+ " "desc": "描述","
+ " "subject": "主题","
+ " "attach": "3245,3456,4345,4553","
+ " "data": {"
+ " "desc": "测试对象","
+ " "dataid": "22","
+ " "billno": "TEST0001","
+ " "datarelation":["
+ " {"
+ " "dataname": "关联对象1","
+ " "data": ["
+ " {"
+ " "dataid": "22","
+ " "datalineid": "1","
+ " "content1": "test1","
+ " "content2": "test2""
+ " }"
+ " ]"
+ " }"
+ " ]"
+ " }"
+ " }";
System.out.println(jsonStr+":"+new JsonValidator().validate(jsonStr));
}
}