Java JSON组成和解析
本框架JSON元素组成和分析，JsonElement分三大类型JsonArray，JsonObject，JsonString。
JsonArray:数组和Collection子类，指定数组的话，使用ArrayList来add元素，遍历ArrayList再使用Array.newInstance生成数组并添加元素即可.
JsonObject:带有泛型的封装类，给带有泛型的字段赋值，关键在于如何根据“指定的类型”和“Field.getGenericType”来生成新的字段Type。
需要你了解java.lang.reflect.Type的子类
java.lang.reflect.GenericArrayType //通用数组类型 T[]
java.lang.reflect.ParameterizedType //参数类型,如: java.util.List<java.lang.String> java.util.Map<java.lang.String,java.lang.Object>
java.lang.reflect.TypeVariable //类型变量 K,V
java.lang.reflect.WildcardType //通配符类，例如： ?, ? extends Number, ? super Integer
java.lang.Class //int.class User.class byte[].class .....
JsonString:分析字符串并解析成指定的对应类型
下面是本JSON框架的分析图
下面是简陋版的解析代码。该类没有解析日期，数值，转义等代码，只是方便理解解析过程。
package june.zero.json.reader; import java.io.IOException; import java.io.Reader; import java.io.StringReader; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class JsonSimpleParser implements CharSequence { public static void main(String[] args) { String json = "[{a:1,b:2},[1,2,3]]"; Object obj = new JsonSimpleParser().parse(json); System.out.println(obj); } protected static final String JSON_EXTRA_CHAR_ERROR = "Extra characters exist! "; protected static final String JSON_OBJECT_COLON_ERROR = "Wrong format of JsonObject, no separator colon! "; protected static final String JSON_OBJECT_END_ERROR = "The JsonObject format must end with comma as a separator or with right curly brace! "; protected static final String JSON_ARRAY_END_ERROR = "The JsonArray format must end with comma as a separator or with right bracket! "; protected static final String JSON_STRING2_END_ERROR = "The character starts with double quotation marks, but does not end with double quotation marks! "; protected static final String JSON_STRING1_END_ERROR = "The character starts with single quotation marks, but does not end with single quotation marks! "; protected Reader reader; protected static final int capacity = 1024; protected final char[] cache = new char[capacity]; protected int count; protected int position; public void read() throws IOException { this.position = 0; this.count = this.reader.read(this.cache,0,capacity); } /** * 当前指针指向的字符 * @return */ public char current() { if(this.count==-1) return '\uffff'; return this.cache[this.position]; } /** * 当前指针指向的索引下标 * @return */ public int position() { return this.position; } /** * 指针指向下一个字符，判断是否需要重新读取数据 * @return * @throws IOException */ public boolean nextRead() throws IOException { return ++this.position>=this.count; } /** * 指针指向下一个字符 * @return * @throws IOException */ public void next() throws IOException { if(++this.position>=this.count){ this.position = 0; this.count = this.reader.read(this.cache,0,capacity); } } /** * 跳过空白字符 * @throws IOException */ public void skip() throws IOException { while(this.count!=-1&&Character.isWhitespace(this.current())){ if(++this.position>=this.count){ this.position = 0; this.count = this.reader.read(this.cache,0,capacity); } } } public Object parse(String json) throws RuntimeException { return parse(new StringReader(json)); } /** * 解析 */ public Object parse(Reader reader) throws RuntimeException { try { this.reader = reader; this.read(); Object value = parse(); this.skip(); if(this.count!=-1){ throw new RuntimeException(JSON_EXTRA_CHAR_ERROR); } return value; } catch (Throwable e) { throw new RuntimeException(e); } finally { try { this.close(); } catch (IOException e) { } } } protected Object parse() throws IOException { this.skip(); char current = this.current(); if(current=='{'){ this.next(); this.skip(); Map<Object, Object> object = new HashMap<Object, Object>(); if(this.current() == '}') { this.next(); return object; } do{ Object key = parse(); this.skip(); if(this.current()!=':'){ throw new RuntimeException(JSON_OBJECT_COLON_ERROR); } this.next(); object.put(key, parse()); this.skip(); current = this.current(); if(current=='}') break; if(current!=','){ throw new RuntimeException(JSON_OBJECT_END_ERROR); } this.next(); }while(true); this.next(); return object; } if(current=='['){ this.next(); this.skip(); List<Object> array = new ArrayList<Object>(); if(this.current() == ']'){ this.next(); return array; } do{ array.add(parse()); this.skip(); current = this.current(); if(current==']') break; if(current!=','){ throw new RuntimeException(JSON_ARRAY_END_ERROR); } this.next(); }while(true); this.next(); return array; } StringBuilder string = new StringBuilder(); if(current=='"'){ this.next(); int offset = this.position; while(this.count!=-1&& this.current()!='"'){ if(this.nextRead()){ string.append(this, offset, this.position); offset = 0; this.position = 0; this.count = this.reader.read(this.cache,0,capacity); } } string.append(this, offset, this.position); if(this.current()!='"'){ throw new RuntimeException(JSON_STRING2_END_ERROR); } this.next(); return string; } if(current=='\''){ this.next(); int offset = this.position; while(this.count!=-1&&this.current()!='\''){ if(this.nextRead()){ string.append(this, offset, this.position); offset = 0; this.read(); } } string.append(this, offset, this.position); if(this.current()!='\''){ throw new RuntimeException(JSON_STRING1_END_ERROR); } this.next(); return string; } int offset = this.position; while(this.count!=-1&& (current = this.current())!=','&& current!=':'&& current!=']'&& current!='}'&& !Character.isWhitespace(current)){ if(this.nextRead()){ string.append(this, offset, this.position); offset = 0; this.read(); } } string.append(this, offset, this.position); return string; } /** * 关闭流 * @throws IOException */ public void close() throws IOException{ if(this.reader!=null){ this.reader.close(); this.reader = null; } } @Override public char charAt(int index) { return this.cache[index]; } @Override public int length() { return this.count; } @Override public CharSequence subSequence(int start, int end) { if (start < 0) throw new StringIndexOutOfBoundsException(start); if (end > count) throw new StringIndexOutOfBoundsException(end); if (start > end) throw new StringIndexOutOfBoundsException(end - start); StringBuilder string = new StringBuilder(); for (int i = start; i < end; i++) { string.append(this.cache[i]); } return string; } @Override public String toString() { if(this.count<0) return null; return new String(this.cache,this.position,this.count-this.position); } }
转载请标明该来源。https://www.cnblogs.com/JuneZero/p/18252639
源码和jar包及其案例：https://www.cnblogs.com/JuneZero/p/18237283
