Java JSON組成和解析

　　本框架JSON元素組成和分析，JsonElement分三大類型JsonArray，JsonObject，JsonString。

　　JsonArray:數組和Collection子類，指定數組的話，使用ArrayList來add元素，遍歷ArrayList再使用Array.newInstance生成數組並添加元素即可.

　　JsonObject:帶有泛型的封裝類，給帶有泛型的欄位賦值，關鍵在於如何根據“指定的類型”和“Field.getGenericType”來生成新的欄位Type。

　　　　需要你瞭解java.lang.reflect.Type的子類

　　　　java.lang.reflect.GenericArrayType   //通用數組類型 T[]
　　　　java.lang.reflect.ParameterizedType //參數類型,如:  java.util.List<java.lang.String>    java.util.Map<java.lang.String,java.lang.Object>
　　　　java.lang.reflect.TypeVariable  //類型變數 K,V
　　　　java.lang.reflect.WildcardType //通配符類，例如： ?, ? extends Number, ? super Integer

　　　　java.lang.Class  //int.class User.class .....

　　JsonString:分析字元串並解析成指定的對應類型

　　下麵是本JSON框架的分析圖

下麵是簡陋版的解析代碼。該類沒有解析日期，數值等代碼，只是方便理解解析過程。

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);
    }
    
    /**
     * 當前指針指向的字元
     * @return
     */
    public char current() {
        if(this.count==-1) return '\uffff';
        return this.cache[this.position];
    }
    /**
     * 當前指針指向的索引下標
     * @return
     */
    public int position() {
        return this.position;
    }

    /**
     * 指針指向下一個字元，判斷是否需要重新讀取數據
     * @return
     * @throws IOException
     */
    public boolean nextRead() throws IOException {
        return ++this.position>=this.count;
    }
    
    /**
     * 指針指向下一個字元
     * @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);
        }
    }
    /**
     * 跳過空白字元
     * @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();
                this.skip();
            }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();
                this.skip();
            }while(true);
            this.next();
            return array;
        }
        this.skip();
        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=='\''){
            if(++this.position>=this.count){
                this.position = 0;
                this.count = this.reader.read(this.cache,0,capacity);
            }
            
            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;
    }
    
    /**
     * 關閉流
     * @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);
    }
    
}

轉載請標明該來源。https://www.cnblogs.com/JuneZero/p/18252639

源碼和jar包及其案例：https://www.cnblogs.com/JuneZero/p/18237283