java入门，JSONObject实现源码解析

一、前言

现在写java程序，很少需要写一些底层的数据结构和算法，因为这些轮子早已造好，拿来用就行。比如在代码中我们经常用到的这个类JSONObject ，还有我们经常使用的String类型，它都是有底层实现的，我们直接引用别人开发的java包就行了，无需要关心它是如何实现的， 所以平时开发其实对于底层的东西了解越来越少，这一节就分析一下JSONObject的源码，看它是如何实现的。

二、JSONObject源码

package com.alibaba.fastjson;

import static com.alibaba.fastjson.util.TypeUtils.castToBigDecimal;
import static com.alibaba.fastjson.util.TypeUtils.castToBigInteger;
import static com.alibaba.fastjson.util.TypeUtils.castToBoolean;
import static com.alibaba.fastjson.util.TypeUtils.castToByte;
import static com.alibaba.fastjson.util.TypeUtils.castToBytes;
import static com.alibaba.fastjson.util.TypeUtils.castToDate;
import static com.alibaba.fastjson.util.TypeUtils.castToDouble;
import static com.alibaba.fastjson.util.TypeUtils.castToFloat;
import static com.alibaba.fastjson.util.TypeUtils.castToInt;
import static com.alibaba.fastjson.util.TypeUtils.castToLong;
import static com.alibaba.fastjson.util.TypeUtils.castToShort;
import static com.alibaba.fastjson.util.TypeUtils.castToSqlDate;
import static com.alibaba.fastjson.util.TypeUtils.castToTimestamp;

import java.io.*;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.*;

import com.alibaba.fastjson.annotation.JSONField;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.parser.ParserConfig;
import com.alibaba.fastjson.util.TypeUtils;


public class JSONObject extends JSON implements Map, Cloneable, Serializable, InvocationHandler {

    private static final long         serialVersionUID         = 1L;
    private static final int          DEFAULT_INITIAL_CAPACITY = 16;

    private final Map map;

    public JSONObject(){
        this(DEFAULT_INITIAL_CAPACITY, false);
    }

    public JSONObject(Map map){
        if (map == null) {
            throw new IllegalArgumentException("map is null.");
        }
        this.map = map;
    }

    public JSONObject(boolean ordered){
        this(DEFAULT_INITIAL_CAPACITY, ordered);
    }

    public JSONObject(int initialCapacity){
        this(initialCapacity, false);
    }

    public JSONObject(int initialCapacity, boolean ordered){
        if (ordered) {
            map = new LinkedHashMap(initialCapacity);
        } else {
            map = new HashMap(initialCapacity);
        }
    }

    public int size() {
        return map.size();
    }

    public boolean isEmpty() {
        return map.isEmpty();
    }

    public boolean containsKey(Object key) {
        boolean result = map.containsKey(key);
        if (!result) {
            if (key instanceof Number
                    || key instanceof Character
                    || key instanceof Boolean
                    || key instanceof UUID
            ) {
                result = map.containsKey(key.toString());
            }
        }
        return result;
    }

    public boolean containsValue(Object value) {
        return map.containsValue(value);
    }

    public Object get(Object key) {
        Object val = map.get(key);

        if (val == null) {
            if (key instanceof Number
                    || key instanceof Character
                    || key instanceof Boolean
                    || key instanceof UUID
            ) {
                val = map.get(key.toString());
            }
        }

        return val;
    }

    public Object getOrDefault(Object key, Object defaultValue) {
        Object v;
        return ((v = get(key)) != null) ? v : defaultValue;
    }

    public JSONObject getJSONObject(String key) {
        Object value = map.get(key);

        if (value instanceof JSONObject) {
            return (JSONObject) value;
        }

        if (value instanceof Map) {
            return new JSONObject((Map) value);
        }

        if (value instanceof String) {
            return JSON.parseObject((String) value);
        }

        return (JSONObject) toJSON(value);
    }

    public JSONArray getJSONArray(String key) {
        Object value = map.get(key);

        if (value instanceof JSONArray) {
            return (JSONArray) value;
        }

        if (value instanceof List) {
            return new JSONArray((List) value);
        }

        if (value instanceof String) {
            return (JSONArray) JSON.parse((String) value);
        }

        return (JSONArray) toJSON(value);
    }

    public  T getObject(String key, Class clazz) {
        Object obj = map.get(key);
        return TypeUtils.castToJavaBean(obj, clazz);
    }

    public  T getObject(String key, Type type) {
        Object obj = map.get(key);
        return TypeUtils.cast(obj, type, ParserConfig.getGlobalInstance());
    }

    public  T getObject(String key, TypeReference typeReference) {
        Object obj = map.get(key);
        if (typeReference == null) {
            return (T) obj;
        }
        return TypeUtils.cast(obj, typeReference.getType(), ParserConfig.getGlobalInstance());
    }

    public Boolean getBoolean(String key) {
        Object value = get(key);

        if (value == null) {
            return null;
        }

        return castToBoolean(value);
    }

    public byte[] getBytes(String key) {
        Object value = get(key);

        if (value == null) {
            return null;
        }

        return castToBytes(value);
    }

    public boolean getBooleanValue(String key) {
        Object value = get(key);

        Boolean booleanVal = castToBoolean(value);
        if (booleanVal == null) {
            return false;
        }

        return booleanVal.booleanValue();
    }

    public Byte getByte(String key) {
        Object value = get(key);

        return castToByte(value);
    }

    public byte getByteValue(String key) {
        Object value = get(key);

        Byte byteVal = castToByte(value);
        if (byteVal == null) {
            return 0;
        }

        return byteVal.byteValue();
    }

    public Short getShort(String key) {
        Object value = get(key);

        return castToShort(value);
    }

    public short getShortValue(String key) {
        Object value = get(key);

        Short shortVal = castToShort(value);
        if (shortVal == null) {
            return 0;
        }

        return shortVal.shortValue();
    }

    public Integer getInteger(String key) {
        Object value = get(key);

        return castToInt(value);
    }

    public int getIntValue(String key) {
        Object value = get(key);

        Integer intVal = castToInt(value);
        if (intVal == null) {
            return 0;
        }

        return intVal.intValue();
    }

    public Long getLong(String key) {
        Object value = get(key);

        return castToLong(value);
    }

    public long getLongValue(String key) {
        Object value = get(key);

        Long longVal = castToLong(value);
        if (longVal == null) {
            return 0L;
        }

        return longVal.longValue();
    }

    public Float getFloat(String key) {
        Object value = get(key);

        return castToFloat(value);
    }

    public float getFloatValue(String key) {
        Object value = get(key);

        Float floatValue = castToFloat(value);
        if (floatValue == null) {
            return 0F;
        }

        return floatValue.floatValue();
    }

    public Double getDouble(String key) {
        Object value = get(key);

        return castToDouble(value);
    }

    public double getDoubleValue(String key) {
        Object value = get(key);

        Double doubleValue = castToDouble(value);
        if (doubleValue == null) {
            return 0D;
        }

        return doubleValue.doubleValue();
    }

    public BigDecimal getBigDecimal(String key) {
        Object value = get(key);

        return castToBigDecimal(value);
    }

    public BigInteger getBigInteger(String key) {
        Object value = get(key);

        return castToBigInteger(value);
    }

    public String getString(String key) {
        Object value = get(key);

        if (value == null) {
            return null;
        }

        return value.toString();
    }

    public Date getDate(String key) {
        Object value = get(key);

        return castToDate(value);
    }

    public Object getSqlDate(String key) {
        Object value = get(key);

        return castToSqlDate(value);
    }

    public Object getTimestamp(String key) {
        Object value = get(key);

        return castToTimestamp(value);
    }

    public Object put(String key, Object value) {
        return map.put(key, value);
    }

    public JSONObject fluentPut(String key, Object value) {
        map.put(key, value);
        return this;
    }

    public void putAll(Map m) {
        map.putAll(m);
    }

    public JSONObject fluentPutAll(Map m) {
        map.putAll(m);
        return this;
    }

    public void clear() {
        map.clear();
    }

    public JSONObject fluentClear() {
        map.clear();
        return this;
    }

    public Object remove(Object key) {
        return map.remove(key);
    }

    public JSONObject fluentRemove(Object key) {
        map.remove(key);
        return this;
    }

    public Set keySet() {
        return map.keySet();
    }

    public Collection