如何用fastjson处理超大对象和超大JSON文本
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来看一下示例代码:
示例对象:
package json.fastjson.StreamApi;import java.util.HashMap;import java.util.Map;public class VO {private int id;private Mapattributes = new HashMap ();public VO(int id) {super();this.id = id; }public int getId() {return id; }public void setId(int id) {this.id = id; }public Map getAttributes() {return attributes; }@Overridepublic String toString() {return "VO [id=" + id + ", attributes=" + attributes + "]"; } }
一、序列化
1.1、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。
测试类:
package json.fastjson.StreamApi;import java.io.FileWriter;import java.io.IOException;import com.alibaba.fastjson.JSONWriter;public class TestHugeArraySerialize {public static void main(String[] args) throws IOException { JSONWriter writer = new JSONWriter(new FileWriter("hugeArray.json")); writer.startArray();for (int i = 0; i < 10; ++i) { writer.writeValue(new VO(i)); } writer.endArray(); writer.close(); } }
输出结果:
程序运行之后会产生一个文件:
文件内容:
[{"attributes":{},"id":0},{"attributes":{},"id":1},{"attributes":{},"id":2},{"attributes":{},"id":3},{"attributes":{},"id":4},{"attributes":{},"id":5},{"attributes":{},"id":6},{"attributes":{},"id":7},{"attributes":{},"id":8},{"attributes":{},"id":9}]
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1.2、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。
测试类:
package json.fastjson.StreamApi;import java.io.FileWriter;import java.io.IOException;import com.alibaba.fastjson.JSONWriter;public class TestHugeObjectSerialize {public static void main(String[] args) throws IOException { JSONWriter writer = new JSONWriter(new FileWriter("hugeObject.json")); writer.startObject();for (int i = 0; i < 10; ++i) { writer.writeKey("x" + i); writer.writeValue(new VO(i)); } writer.endObject(); writer.close(); } }
输出结果:
程序运行之后会产生一个文件:
文件内容:
{"x0":{"attributes":{},"id":0},"x1":{"attributes":{},"id":1},"x2":{"attributes":{},"id":2},"x3":{"attributes":{},"id":3},"x4":{"attributes":{},"id":4},"x5":{"attributes":{},"id":5},"x6":{"attributes":{},"id":6},"x7":{"attributes":{},"id":7},"x8":{"attributes":{},"id":8},"x9":{"attributes":{},"id":9}}
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二、反序列化
2.1、超大JSON数组反序列化
测试类:
package json.fastjson.StreamApi;import java.io.FileReader;import java.io.IOException;import com.alibaba.fastjson.JSONReader;public class TestHugeArrayDeserialize {public static void main(String[] args) throws IOException {// 读入上面输出的文件JSONReader reader = new JSONReader(new FileReader("hugeArray.json")); reader.startArray();while (reader.hasNext()) { VO vo = reader.readObject(VO.class); System.out.println(vo); } reader.endArray(); reader.close(); } }
输出结果:
VO [id=0, attributes={}]VO [id=1, attributes={}]VO [id=2, attributes={}]VO [id=3, attributes={}]VO [id=4, attributes={}]VO [id=5, attributes={}]VO [id=6, attributes={}]VO [id=7, attributes={}]VO [id=8, attributes={}]VO [id=9, attributes={}]
2.2、超大JSON对象反序列化
测试类:
package json.fastjson.StreamApi;import java.io.FileReader;import java.io.IOException;import com.alibaba.fastjson.JSONReader;public class TestHugeObjectDeserialize {public static void main(String[] args) throws IOException {// 读入上面输出的文件JSONReader reader = new JSONReader(new FileReader("hugeObject.json")); reader.startObject();while (reader.hasNext()) { String key = reader.readString(); VO vo = reader.readObject(VO.class); System.out.println(key + ":" + vo); } reader.endObject(); reader.close(); } }
输出结果:
x0:VO [id=0, attributes={}]x1:VO [id=1, attributes={}]x2:VO [id=2, attributes={}]x3:VO [id=3, attributes={}]x4:VO [id=4, attributes={}]x5:VO [id=5, attributes={}]x6:VO [id=6, attributes={}]x7:VO [id=7, attributes={}]x8:VO [id=8, attributes={}]x9:VO [id=9, attributes={}]
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