java - 当我基于 json 数组创建 json 对象时内存不足

Question

我在 java 中创建了一个 Web 服务来返回 json 数据。好的，对于小数据没问题，但是当我处理大数据时，它会返回内存不足错误。

查看我的代码:

public void getImages() throws Exception {
      JSONObject o = new JSONObject();
      JSONArray jsonArray = new JSONArray();

      try {
                Class.forName(DRIVERNAME);
                conn = DriverManager.getConnection(URL, USER, PASS);

                Statement s = connection.createStatement();
                ResultSet r = s.executeQuery("select * from images");

                while (r.next()) {
                          JSONObject obj = new JSONObject();

                          obj.put("id", r.getInt("id"));

                          byte[] iBytes = r.getBytes("image");
                          String iBase64 = DatatypeConverter.printBase64Binary(iBytes);
                          obj.put("image", iBase64);

                          jsonArray.put(obj);
                }

                o.put("images", jsonArray);

      } catch (SQLException e) {

      }
}

在 jsonArray 中添加图像时发生内存不足(java.lang.OutOfMemoryError:Java 堆空间):

byte[] iBytes = r.getBytes("image");
String iBase64 = DatatypeConverter.printBase64Binary(iBytes);
obj.put("image", iBase64);

知道如何解决这个问题吗？

Answer 1

使用 Jackson 库中的流 json(ObjectMapper、JsonFactory、JsonGenerator)解决您的问题。请看下面的代码:

public void getImages() throws Exception {

    ObjectMapper objectMapper = new ObjectMapper();
    JsonFactory jf = objectMapper.getFactory();
    JsonGenerator jg = f.createGenerator(new File("c:\\images.json"), JsonEncoding.UTF8);

    try {
        Class.forName(DRIVERNAME);
        conn = DriverManager.getConnection(URL, USER, PASS);

        Statement s = connection.createStatement();
        ResultSet r = s.executeQuery("select * from images");

        jg.writeFieldName("images");
        jg.writeStartArray();

        while (r.next()) {
           jg.writeBinary(r.getBinaryStream("IMAGEM"), -1);
           in.close();
        }

        jg.writeEndArray(); 
        jg.writeEndObject(); 
        jg.close();

    } catch (SQLException e) {
        //use the exceptions
    }
}