php语言中使用json的技巧及json的实现代码详解

目前，JSON已经成为最流行的数据交换格式之一，各大网站的API几乎都支持它。

我写过一篇《数据类型和JSON格式》，探讨它的设计思想。今天，我想总结一下PHP语言对它的支持，这是开发互联网应用程序（特别是编写API）必须了解的知识。

从5.2版本开始，PHP原生提供json_encode()和json_decode()函数，前者用于编码，后者用于解码。

一、json_encode()

该函数主要用来将数组和对象，转换为json格式。先看一个数组转换的例子：

$arr = array ('a'=>1,'b'=>2,'c'=>3,'d'=>4,'e'=>5);
echo json_encode($arr);

结果为

{"a":1,"b":2,"c":3,"d":4,"e":5}

再看一个对象转换的例子：

$obj->body      = 'another post';
$obj->id       = 21;
$obj->approved    = true;
$obj->favorite_count = 1;
$obj->status     = NULL;
echo json_encode($obj);

结果为

{
"body":"another post",　
"id":21,
"approved":true,
"favorite_count":1,
"status":null
}

由于json只接受utf-8编码的字符，所以json_encode()的参数必须是utf-8编码，否则会得到空字符或者null。当中文使用GB2312编码，或者外文使用ISO-8859-1编码的时候，这一点要特别注意。

二、索引数组和关联数组

PHP支持两种数组，一种是只保存"值"（value）的索引数组（indexed array），另一种是保存"名值对"（name/value）的关联数组（associative array）。

由于javascript不支持关联数组，所以json_encode()只将索引数组（indexed array）转为数组格式，而将关联数组（associative array）转为对象格式。

比如，现在有一个索引数组

$arr = Array('one', 'two', 'three');
echo json_encode($arr);

结果为：

["one","two","three"]

如果将它改为关联数组：

$arr = Array('1'=>'one', '2'=>'two', '3'=>'three');
echo json_encode($arr);

结果就变了：

{"1":"one","2":"two","3":"three"}

注意，数据格式从"[]"（数组）变成了"{}"（对象）。

如果你需要将"索引数组"强制转化成"对象"，可以这样写

json_encode( (object)$arr );

或者

json_encode ( $arr, JSON_FORCE_OBJECT );

三、类（class）的转换

下面是一个PHP的类：

class Foo {
const   ERROR_CODE = '404';
public  $public_ex = 'this is public';
private  $private_ex = 'this is private!';
protected $protected_ex = 'this should be protected';
public function getErrorCode() {
return self::ERROR_CODE;
}
}

现在，对这个类的实例进行json转换：

$foo = new Foo;
$foo_json = json_encode($foo);
echo $foo_json;

输出结果是

{"public_ex":"this is public"}

可以看到，除了公开变量（public），其他东西（常量、私有变量、方法等等）都遗失了。

四、json_decode()

该函数用于将json文本转换为相应的PHP数据结构。下面是一个例子：

$json = '{"foo": 12345}';
$obj = json_decode($json);　
print $obj->{'foo'}; // 12345

通常情况下，json_decode()总是返回一个PHP对象，而不是数组。比如：

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
var_dump(json_decode($json));

结果就是生成一个PHP对象：

object(stdClass)#1 (5) {

["a"] => int(1)
["b"] => int(2)
["c"] => int(3)
["d"] => int(4)
["e"] => int(5)

}

如果想要强制生成PHP关联数组，json_decode()需要加一个参数true：

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';
var_dump(json_decode($json,true));

结果就生成了一个关联数组：

array(5) {

 ["a"] => int(1)
 ["b"] => int(2)
 ["c"] => int(3)
 ["d"] => int(4)
 ["e"] => int(5)

}　

五、json_decode()的常见错误

下面三种json写法都是错的，你能看出错在哪里吗？

$bad_json = "{ 'bar': 'baz' }";
$bad_json = '{ bar: "baz" }';
$bad_json = '{ "bar": "baz", }';

对这三个字符串执行json_decode()都将返回null，并且报错。

第一个的错误是，json的分隔符（delimiter）只允许使用双引号，不能使用单引号。第二个的错误是，json名值对的"名"（冒号左边的部分），任何情况下都必须使用双引号。第三个的错误是，最后一个值之后不能添加逗号（trailing comma）。

另外，json只能用来表示对象（object）和数组（array），如果对一个字符串或数值使用json_decode()，将会返回null。

var_dump(json_decode("Hello World")); //null

下面给大家介绍哦php语言的json实现

由于开发一个ajax file manager for web开源项目,数据交换使用的json格式，后来发现在低版本的php上运行会有问题，仔细调试发现json_decode和json_encode无法正常工作，于是查阅资料，发现低版本的php没有实现这两个函数，为了兼容性，我只好自己实现一个php版的json编码解码代码，并保证和json2.js的一致，测试调试并通过，现在将其公布出来，供有相同需求的同学使用：

<?php 
/* * **************************************************************************** 
 * $base: $ 
 * 
 * $Author: $ 
 *   Berlin Qin 
 * 
 * $History: base.js $ 
 *   Berlin Qin  //     created 
 * 
 * $contacted 
 *   [e-mail] 
 *   www.webfmt.com 
 * 
 * *************************************************************************** */ 
/* =========================================================================== 
 * license 
 * 
 * 、Open Source Licenses 
 * webfmt is distributed under the GPL, LGPL and MPL open source licenses. 
 * This triple copyleft licensing model avoids incompatibility with other open source licenses. 
 * These Open Source licenses are specially indicated for: 
 *  Integrating webfmt into Open Source software; 
 *  Personal and educational use of webfmt; 
 *  Integrating webfmt in commercial software, 
 * taking care of satisfying the Open Source licenses terms, 
 *  while not able or interested on supporting webfmt and its development. 
 * 
 * 、Commercial License ? fbis source Closed Distribution License - CDL 
 * For many companies and products, Open Source licenses are not an option. 
 * This is why the fbis source Closed Distribution License (CDL) has been introduced. 
 * It is a non-copyleft license which gives companies complete freedom 
 * when integrating webfmt into their products and web sites. 
 * This license offers a very flexible way to integrate webfmt in your commercial application. 
 * These are the main advantages it offers over an Open Source license: 
 *   Modifications and enhancements doesn't need to be released under an Open Source license; 
 *   There is no need to distribute any Open Source license terms alongside with your product 
 * and no reference to it have to be done; 
 *   No references to webfmt have to be done in any file distributed with your product; 
 *   The source code of webfmt doesn't have to be distributed alongside with your product; 
 *   You can remove any file from webfmt when integrating it with your product. 
 * The CDL is a lifetime license valid for all releases of webfmt published during 
 * and before the year following its purchase. 
 * It's valid for webfmt releases also. It includes year of personal e-mail support. 
 * 
 * ************************************************************************************************************************************************* */ 
function jsonDecode($json) 
{ 
  $result = array(); 
  try 
  { 
    if (PHP_VERSION_ID > ) 
    { 
      $result = (array) json_decode($json); 
    } 
    else 
    { 
      $json = str_replace(array("\\\\", "\\\""), array("&#;", "&#;"), $json); 
      $parts = preg_split("@(\"[^\"]*\")|([\[\]\{\},:])|\s@is", $json, -, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE); 
      foreach ($parts as $index => $part) 
      { 
        if (strlen($part) == ) 
        { 
          switch ($part) 
          { 
            case "[": 
            case "{": 
              $parts[$index] = "array("; 
              break; 
            case "]": 
            case "}": 
              $parts[$index] = ")"; 
              break; 
            case ":": 
              $parts[$index] = "=>"; 
              break; 
            case ",": 
              break; 
            default: 
              break; 
          } 
        } 
      } 
      $json = str_replace(array("&#;", "&#;", "$"), array("\\\\", "\\\"", "\\$"), implode("", $parts)); 
      $result = eval("return $json;"); 
    } 
  } 
  catch (Exception $e) 
  { 
    $result = array("error" => $e->getCode()); 
  } 
  return $result; 
} 
function valueTostr($val) 
{ 
  if (is_string($val))  
  { 
    $val = str_replace('\"', "\\\"", $val); 
    $val = str_replace("\\", "\\\\", $val); 
    $val = str_replace("/", "\\/", $val); 
    $val = str_replace("\t", "\\t", $val); 
    $val = str_replace("\n", "\\n", $val); 
    $val = str_replace("\r", "\\r", $val); 
    $val = str_replace("\b", "\\b", $val); 
    $val = str_replace("\f", "\\f", $val); 
    return '"' . $val . '"'; 
  } 
  elseif (is_int($val)) 
    return sprintf('%d', $val); 
  elseif (is_float($val)) 
    return sprintf('%F', $val); 
  elseif (is_bool($val)) 
    return ($val ? 'true' : 'false'); 
  else 
    return 'null'; 
} 
function jsonEncode($arr) 
{ 
  $result = "{}"; 
  try 
  { 
    if (PHP_VERSION_ID > ) 
    { 
      $result = json_encode($arr); 
    } 
    else 
    { 
      $parts = array(); 
      $is_list = false; 
      if (!is_array($arr)) 
      { 
        $arr = (array) $arr; 
      } 
      $end = count($arr) - ; 
      if (count($arr) > ) 
      { 
        if (is_numeric(key($arr))) 
        { 
          $result = "[";  
          for ($i = ; $i < count($arr); $i++) 
          { 
            if (is_array($arr[$i])) 
            { 
              $result = $result . jsonEncode($arr[$i]); 
            } 
            else 
            { 
              $result = $result . valueTostr($arr[$i]); 
            } 
            if ($i != $end) 
            { 
              $result = $result . ","; 
            } 
          } 
          $result = $result . "]"; 
        } 
        else 
        { 
          $result = "{";  
          $i = ; 
          foreach ($arr as $key => $value) 
          { 
            $result = $result . '"' . $key . '":'; 
            if (is_array($value)) 
            { 
              $result = $result . jsonEncode($value); 
            } 
            else 
            { 
              $result = $result . valueTostr($value); 
            } 
            if ($i != $end) 
            { 
              $result = $result . ","; 
            } 
            $i++; 
          } 
          $result = $result . "}"; 
        } 
      } 
      else 
      { 
        $result = "[]"; 
      } 
    } 
  } 
  catch (Exception $e) 
  { 
  } 
  return $result; 
} 
?>

如果使用过程有什么问题，可以给我email.欢迎大家指出错误！