JSON数据的解析

JSONObject的使用

一、 JSON对象的使用：

String content = "{'username': 'linux', 'password': '123456'}";JSONObject jsonObject = new JSONObject(content);String username = jsonObject.getString("username");String password = jsonObject.getString("password");

二、 JSON数组的使用：

String jsonContent = "[{'user': '刘力', 'age': 21, 'femal': true}, "+ "{'user': 'chen', 'age': 20, 'femal': false}]";JSONArray jsonArray = new JSONArray(jsonContent);for (int i = 0; i < jsonArray.length; i++) {JSONObject object = jsonArray.getJSONObject(i);System.out.print(object.getString("user") + " ");System.out.print(object.getInt("age") + " ");System.out.print(object.getBoolean("femal") + " ");System.out.println;}

三、 JSON数组与JSON对象混合使用

String jsonString = "[{'user': 'tomhu', 'age': 21, " + "'info': {'adress': 'hubai', 'sex': 'femal'}}, " + "{'user': 'chen', 'age': 20, " + "'info': {'adress': 'hunan', 'sex': 'male'}}]";JSONArray jsonArrays = new JSONArray(jsonString);for (int i = 0; i < jsonArrays.length; i++) {    JSONObject objects = jsonArrays.getJSONObject(i);    System.out.print(objects.getString("user") + " ");    System.out.print(objects.getInt("age") + " ");    System.out.print(objects.getJSONObject("info").getString("adress") + " ");    System.out.print(objects.getJSONObject("info").getString("sex") + " ");    System.out.println;}

四、 JSON数组中存储对象

Person person = new Person;person.setUsername("linux" );person.setPassword("123456" );JSONArray jsonArray = new JSONArray;jsonArray.put(0, person );jsonArray.put(1, "I love you" );// String username = jsonArray.getJSONObject(0).getString("username");  错误的写法Person user = (Person) jsonArray.get(0);System.out.println("username: " + user.getUsername);

JSONObject的原理

JsonObject的存储与取出

一、 JSONObject里面维护了一个LinkedHashMap，当生成一个无参数的JSONObject，实质是初始化了一个Map：

private final LinkedHashMap<String, Object> nameValuePairs;public JSONObject {    nameValuePairs = new LinkedHashMap<String, Object>;}

二、 当JSONObject增加数据，实质上把数据的键值对方法存放在上述的Map中：

public JSONObject put(String name, boolean value) throws JSONException {    nameValuePairs.put(checkName(name), value);    return this;}

三、 从JSONObject中取出数据，很容易想到的就是从Map取出了：

public String getString(String name) throws JSONException {    Object object = get(name);  // get方法就是执行Object result = nameValuePairs.get(name);    String result = JSON.toString(object);    if (result == null) {        throw JSON.typeMismatch(name, object, "String");    }    return result;}

JsonObject的解析过程

一、 JsonObject还有一个带参数的构造函数：常用的是传递一个String类型的参数

public JSONObject(String json) throws JSONException {    this(new JSONTokener(json));}

二、 跟进去，发现主要执行的是JSONTokener的nextValue方法，在这个方法中主要是对数据进行解析;

public Object nextValue throws JSONException {    int c = nextCleanInternal;    switch (c) {        case -1: throw syntaxError("End of input");        case '{': return readObject;        case '[': return readArray;        case '\'':        case '"': return nextString((char) c);        default: pos--; return readLiteral;    }}

• 在nextCleanInternal方法中，它会从头到尾的逐个字符的解析，对于一些字符做一些处理。例如空格，换行，转义符等！
• 当解析到[表示开始一个对象的读取，当解析到{表示一个数组的读取

三、 在readObject方法中，仍然是调用nextCleanInternal方法，逐个得到解析的字符，下到解析到}.下面贴出重要代码

int first = nextCleanInternal;  // 得到解析的字符if (first == '}') {    return result;} else if (first != -1) {    pos--;}.......while (true) {    Object name = nextValue;  // 解析得到键        int separator = nextCleanInternal;    if (separator != ':' && separator != '=') {        throw syntaxError("Expected ':' after " + name);    }    if (pos < in.length && in.charAt(pos) == '>') {        pos++;    }    result.put((String) name, nextValue);  // 将解析得到的键值对，存放在map当中    switch (nextCleanInternal) {        case '}': return result;        case ';':        case ',': continue;        default: throw syntaxError("Unterminated object");    }}

四、 nextValue方法比较关键，它流转解析的大部分工作！在nextValue中有一个readLiteral方法，针对一些类型做处理，得到解析之后的结果：

private Object readLiteral throws JSONException {    String literal = nextToInternal("{}[]/\\:,=;# \t\f");    if (literal.length == 0) {        throw syntaxError("Expected literal value");    } else if ("null".equalsIgnoreCase(literal)) {        return JSONObject.NULL;    } else if ("true".equalsIgnoreCase(literal)) {        return Boolean.TRUE;    } else if ("false".equalsIgnoreCase(literal)) {        return Boolean.FALSE;    }    /* try to parse as an integral type... */    if (literal.indexOf('.') == -1) {        int base = 10;        String number = literal;        if (number.startsWith("0x") || number.startsWith("0X")) { number = number.substring(2); base = 16;        } else if (number.startsWith("0") && number.length > 1) { number = number.substring(1); base = 8;        }        try { long longValue = Long.parseLong(number, base); if (longValue <= Integer.MAX_VALUE && longValue >= Integer.MIN_VALUE) { return (int) longValue; } else { return longValue; }        } catch (NumberFormatException e) { /* * This only happens for integral numbers greater than * Long.MAX_VALUE, numbers in exponential form (5e-10) and * unquoted strings. Fall through to try floating point. */        }    }    /* ...next try to parse as a floating point... */    try {        return Double.valueOf(literal);    } catch (NumberFormatException ignored) {    }    /* ... finally give up. We have an unquoted string */    return new String(literal); // a new string avoids leaking memory}

五、至于JSONArray的解析与JsonObject的解析过程是一样的，它里面维护的是一个List：

private final List<Object> values;public JSONArray(JSONTokener readFrom) throws JSONException { Object object = readFrom.nextValue; if (object instanceof JSONArray) { values = ((JSONArray) object).values; } else { throw JSON.typeMismatch(object, "JSONArray"); } }

Gson的使用

一、我们在测试当中先加入一个Person类，方便测试：

package com.tomhu.test;public class Person { private String name; private int age; public String getName { return name; } public void setName(String name) { this.name = name; } public int getAge { return age; } public void setAge(int age) { this.age = age; } }

二、 gson把对象转换成JSON格式

Gson gson = new Gson;Person person = new Person;person.setName("linux");person.setAge(23);String str = gson.toJson(person);System.out.println(str);

• 打印结果： {"name":"linux","age":23}

三、 gson把json格式解析成对象

String jsonData = "{'name':'刘力','age':19}";Person person = gson.fromJson(jsonData, Person.class);System.out.println(person.getName + ", " + person.getAge);

四、 gson把List对象解析成Json格式：

Gson gson = new Gson;List<Person> persons = new ArrayList<Person>;for (int i = 0; i < 2; i++) {     Person p = new Person;     p.setName("name" + i);     p.setAge(i * 5);     persons.add(p);}String str = gson.toJson(persons);System.out.println(str);

• 打印结果： [{"name":"name0","age":0},{"name":"name1","age":5}]

五、 gson把Json格式解析成List对象：

Gson gson = new Gson;String str = "[{'name':'linux','age':10},{'name':'huhx','age':22}]";List<Person> ps = gson.fromJson(str, new TypeToken<List<Person>>{}.getType);for (int i = 0; i < ps.size; i++) {    Person person = ps.get(i);    System.out.print("name: " + person.getName + " age: " + person.getAge);}

• 打印结果：name: linux age: 10 name: huhx age: 22