Golang解析JSON遇到的坑及解決方法

type Person struct {
	Name string
	Age  int
}

func main() {
	var p *Person
	bytes, err := json.Marshal(p)
	checkError(err)
	fmt.Printf("len:%d, result:%s\n", len(bytes), string(bytes))  // len:4, result:null
}

func checkError(err error) {
	if err != nil {
		fmt.Printf("err:%+v\n", err)
	}
}

type Person struct {
	Name string
	Age  int
}

func main() {
	var p *Person
	s := `null`
	err := json.Unmarshal([]byte(s), &p)
	checkError(err)
	fmt.Printf("p:%+v\n", p) // p:<nil>
}

func checkValid(data []byte, scan *scanner) error {
	scan.reset()
	for _, c := range data {
		scan.bytes++
		if scan.step(scan, c) == scanError {
			return scan.err
		}
	}
	if scan.eof() == scanError {
		return scan.err
	}
	return nil
}

// stateBeginValue is the state at the beginning of the input.
func stateBeginValue(s *scanner, c byte) int {
	if isSpace(c) {
		return scanSkipSpace
	}
	switch c {
	case '{':
		s.step = stateBeginStringOrEmpty
		return s.pushParseState(c, parseObjectKey, scanBeginObject)
	case '[':
		s.step = stateBeginValueOrEmpty
		return s.pushParseState(c, parseArrayValue, scanBeginArray)
	case '"':
		s.step = stateInString
		return scanBeginLiteral
	case '-':
		s.step = stateNeg
		return scanBeginLiteral
	case '0': // beginning of 0.123
		s.step = state0
		return scanBeginLiteral
	case 't': // beginning of true
		s.step = stateT
		return scanBeginLiteral
	case 'f': // beginning of false
		s.step = stateF
		return scanBeginLiteral
	case 'n': // beginning of null
		s.step = stateN
		return scanBeginLiteral
	}
	if '1' <= c && c <= '9' { // beginning of 1234.5
		s.step = state1
		return scanBeginLiteral
	}
	return s.error(c, "looking for beginning of value")
}

// stateN is the state after reading `n`.
func stateN(s *scanner, c byte) int {
	if c == 'u' {
		s.step = stateNu
		return scanContinue
	}
	return s.error(c, "in literal null (expecting 'u')")
}

// stateNu is the state after reading `nu`.
func stateNu(s *scanner, c byte) int {
	if c == 'l' {
		s.step = stateNul
		return scanContinue
	}
	return s.error(c, "in literal null (expecting 'l')")
}

// stateNul is the state after reading `nul`.
func stateNul(s *scanner, c byte) int {
	if c == 'l' {
		s.step = stateEndValue
		return scanContinue
	}
	return s.error(c, "in literal null (expecting 'l')")
}

type ptrEncoder struct {
	elemEnc encoderFunc
}

func (pe ptrEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
	if v.IsNil() {
		e.WriteString("null")
		return
	}
	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
		// We're a large number of nested ptrEncoder.encode calls deep;
		// start checking if we've run into a pointer cycle.
		ptr := v.Interface()
		if _, ok := e.ptrSeen[ptr]; ok {
			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
		}
		e.ptrSeen[ptr] = struct{}{}
		defer delete(e.ptrSeen, ptr)
	}
	pe.elemEnc(e, v.Elem(), opts)
	e.ptrLevel--
}

type Person struct {
	Name string
	Age  int
}

func main() {
	p := &Person{
		Name: "text",
		Age:  18,
	}

	bytes, err := json.Marshal(p)
	checkError(err)

	pMap := make(map[string]interface{})
	err = json.Unmarshal(bytes, &pMap)
	checkError(err)
	for k, v := range pMap {
		fmt.Printf("k:%s,v:%+v, vtype:%v\n", k, v, reflect.TypeOf(v))
	}
}

func checkError(err error) {
	if err != nil {
		fmt.Printf("err:%+v\n", err)
	}
}