Fastjson toJSONString

Fastjson将java对象序列化为JSON字符串，fastjson提供了一个最简单的入口

package com.alibaba.fastjson;public abstract class JSON {    public static String toJSONString(Object object);}

Sample

import com.alibaba.fastjson.JSON;Model model = new Model();model.id = 1001;String json = JSON.toJSONString(model);

Fastjson writeJSONString

Fastjson在1.2.11版本中，JSON类新增对OutputStream/Writer直接支持。

package com.alibaba.fastjson;public abstract class JSON {   public static final int writeJSONString(OutputStream os, //                                              Object object, //                                              SerializerFeature... features) throws IOException;    public static final int writeJSONString(OutputStream os, //                                             Charset charset, //                                               Object object, //                                              SerializerFeature... features) throws IOException;   public static final int writeJSONString(Writer os, //                                              Object object, //                                              SerializerFeature... features) throws IOException;}

Sample

import com.alibaba.fastjson;import java.nio.charset.Charset;class Model {    public int value;}Model model = new Model();model.value = 1001;OutputStream os = ...;JSON.writeJSONString(os, model);JSON.writeJSONString(os, Charset.from("GB18030"), model);Writer writer = ...;JSON.writeJSONString(writer, model);

Fastjson parseObject InputStream

在1.2.11版本中，fastjson新增加了对InputStream的支持支持。

package com.alibaba.fastjson;public abstract class JSON {    public static 
    
      T parseObject(InputStream is, //                                    Type type, //                                    Feature... features) throws IOException;    public static 
     
       T parseObject(InputStream is, //                                    Charset charset, //                                    Type type, //                                    Feature... features) throws IOException;}
     
    

Sample

import com.alibaba.fastjson;import java.nio.charset.Charset;class Model {    public int value;}InputStream is = ...Model model = JSON.parseObject(is, Model.class);Model model2 = JSON.parseObject(is, Charset.from("UTF-8"), Model.class);

Fastjson当需要处理超大JSON文本时，需要Stream API，在fastjson-1.1.32版本中开始提供Stream API。

超大JSON数组序列化

如果你的JSON格式是一个巨大的JSON数组，有很多元素，则先调用startArray，然后挨个写入对象，然后调用endArray。

JSONWriter writer = new JSONWriter(new FileWriter("/tmp/huge.json"));  writer.startArray();  for (int i = 0; i < 1000 * 1000; ++i) {        writer.writeValue(new VO());  }  writer.endArray();  writer.close();

超大JSON对象序列化

如果你的JSON格式是一个巨大的JSONObject，有很多Key/Value对，则先调用startObject，然后挨个写入Key和Value，然后调用endObject。

JSONWriter writer = new JSONWriter(new FileWriter("/tmp/huge.json"));  writer.startObject();  for (int i = 0; i < 1000 * 1000; ++i) {        writer.writeKey("x" + i);        writer.writeValue(new VO());  }  writer.endObject();  writer.close();

反序列化

例3

JSONReader reader = new JSONReader(new FileReader("/tmp/huge.json"));  reader.startArray();  while(reader.hasNext()) {        VO vo = reader.readObject(VO.class);        // handle vo ...  }  reader.endArray();  reader.close();

例4

JSONReader reader = new JSONReader(new FileReader("/tmp/huge.json"));  reader.startObject();  while(reader.hasNext()) {        String key = reader.readString();        VO vo = reader.readObject(VO.class);        // handle vo ...  }  reader.endObject();  reader.close();

Fastjson DataBind数据库绑定

Fastjson 完全支持数据库绑定方法databind, 也非常易于使用.

Encode

import com.alibaba.fastjson.JSON;Group group = new Group();group.setId(0L);group.setName("admin");User guestUser = new User();guestUser.setId(2L);guestUser.setName("guest");User rootUser = new User();rootUser.setId(3L);rootUser.setName("root");group.addUser(guestUser);group.addUser(rootUser);String jsonString = JSON.toJSONString(group);System.out.println(jsonString);

Output

{"id":0,"name":"admin","users":[{"id":2,"name":"guest"},{"id":3,"name":"root"}]}

Decode

String jsonString = ...;Group group = JSON.parseObject(jsonString, Group.class);