[教程]使用 TQJsonOutputChannel 写入 JSON 数据到流中

TQJsonOutputChannel 的主要作用是用来快速写入大型的 JSON 数据到文件中，所以整体是面向写入过程设计的，不要试图用它来控制内容的修改。

假设我们要将数据内容写入到目标数据流 AStream 中：

第一步：我们需要定义一个 IQJsonStreamEncoder 的实例，它是一个结构体，所以直接在栈上定义这个变量即可。

var
  AWriter: IQJsonStreamEncoder;

1 2	var AWriter: IQJsonStreamEncoder;

第二步：创建实例并建立与目标数据流的关联：

AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);

1	AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);

还有一个最大层数限制，默认为32，可以通过第三个参数修改。

第三步：开始按照正常的规则写入 JSON 数据。

调用 BeginArray 开始一个数组定义，它必需在元素输出完成后，对应一个 EndArray 调用来标志此数组输出结束。也可以使用 WriteArray 来定义数组。
调用 BeginObject 开始一个对象定义，它必需在子结点输出完成后，对应一个 EndObject 调用来标志此对象输出结束。也可以使用 WriteObject 来定义对象。
调用 WriteElement 方法写入数组元素的值
调用 WriteChild 方法写入普通类型的值

第四步：已经完事了，补充一点吧，这个写入的JSON是以压缩格式写入的，没有加入缩进支持。可以用TQJsonInputChannel 来顺序读取。

最后，来一段示例代码，Show you my code:

procedure TForm2.SpeedButton1Click(Sender: TObject);
var
  AStream: TMemoryStream;
  AJson: TQJson;
  I: Integer;
  AWriter: IQJsonStreamEncoder;
begin
  AJson := AcquireJson;
  AStream := TMemoryStream.Create;
  try
    AJson.Add('O').Add('01');
    AJson.AddArray('A');
    AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);
    AWriter.BeginArray('');
    for I := 0 to 9 do
    begin
      AWriter.BeginObject('');
      AWriter.WriteChild('Ident', 'Json Stream Writer');
      AWriter.WriteChild('IntValue', I);
      AWriter.WriteChild('FloatValue', Double(1.333 * I));
      AWriter.WriteChild('BoolValue', (I mod 2) = 1);
      AWriter.WriteChild('NullValue');
      AWriter.WriteChild('DateTime', Now);
      AJson.ForcePath('O.01').AsString := I.ToString;
      AWriter.WriteChild('Json', AJson);
      AWriter.EndObject;
    end;
    AWriter.EndArray;
    AStream.Position := 0;
    repeat
      AJson.LoadFromStream(AStream, teUtf8);
      ShowMessage(AJson.Encode(true));
    until AStream.Position = AStream.Size;

  finally
    ReleaseJson(AJson);
    FreeAndNil(AStream);
  end;
end;

procedure TForm2.SpeedButton2Click(Sender: TObject);
var
  AStream: TMemoryStream;
  AJson: TQJson;
  I: Integer;
  AWriter: IQJsonStreamEncoder;
begin
  AJson := AcquireJson;
  AStream := TMemoryStream.Create;
  try
    AJson.Add('O').Add('01');
    AJson.AddArray('A');
    AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);
    AWriter.WriteArray('',
      procedure(AParent: IQJsonArrayEncoder)
      var
        I: Integer;
      begin
        for I := 0 to 9 do
        begin
          AParent.WriteObject(
            procedure(AObjParent: IQJsonObjectEncoder)
            begin
              AObjParent.Write('Ident', 'Json Stream Writer');
              AObjParent.Write('IntValue', I);
              AObjParent.Write('FloatValue', Double(1.333 * I));
              AObjParent.Write('BoolValue', (I mod 2) = 1);
              AObjParent.Write('NullValue');
              AObjParent.Write('DateTime', Now);
              AJson.ForcePath('O.01').AsString := I.ToString;
              AObjParent.Write('Json', AJson);
            end);
        end
      end);
    AStream.Position := 0;
    repeat
      AJson.LoadFromStream(AStream, teUtf8);
      ShowMessage(AJson.Encode(true));
    until AStream.Position = AStream.Size;
  finally
    ReleaseJson(AJson);
    FreeAndNil(AStream);
  end;
end;

procedure TForm2.SpeedButton1Click(Sender: TObject);

var

AStream: TMemoryStream;

AJson: TQJson;

I: Integer;

AWriter: IQJsonStreamEncoder;

begin

AJson := AcquireJson;

AStream := TMemoryStream.Create;

try

AJson.Add('O').Add('01');

AJson.AddArray('A');

AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);

AWriter.BeginArray('');

for I := 0 to 9 do

begin

AWriter.BeginObject('');

AWriter.WriteChild('Ident', 'Json Stream Writer');

AWriter.WriteChild('IntValue', I);

AWriter.WriteChild('FloatValue', Double(1.333 * I));

AWriter.WriteChild('BoolValue', (I mod 2) = 1);

AWriter.WriteChild('NullValue');

AWriter.WriteChild('DateTime', Now);

AJson.ForcePath('O.01').AsString := I.ToString;

AWriter.WriteChild('Json', AJson);

AWriter.EndObject;

end;

AWriter.EndArray;

AStream.Position := 0;

repeat

AJson.LoadFromStream(AStream, teUtf8);

ShowMessage(AJson.Encode(true));

until AStream.Position = AStream.Size;

finally

ReleaseJson(AJson);

FreeAndNil(AStream);

end;

procedure TForm2.SpeedButton2Click(Sender: TObject);

var

AStream: TMemoryStream;

AJson: TQJson;

I: Integer;

AWriter: IQJsonStreamEncoder;

begin

AJson := AcquireJson;

AStream := TMemoryStream.Create;

try

AJson.Add('O').Add('01');

AJson.AddArray('A');

AWriter := TQJsonOutputChannel.CreateEncoder(teUtf8, AStream);

AWriter.WriteArray('',

procedure(AParent: IQJsonArrayEncoder)

var

I: Integer;

begin

for I := 0 to 9 do

begin

AParent.WriteObject(

procedure(AObjParent: IQJsonObjectEncoder)

begin

AObjParent.Write('Ident', 'Json Stream Writer');

AObjParent.Write('IntValue', I);

AObjParent.Write('FloatValue', Double(1.333 * I));

AObjParent.Write('BoolValue', (I mod 2) = 1);

AObjParent.Write('NullValue');

AObjParent.Write('DateTime', Now);

AJson.ForcePath('O.01').AsString := I.ToString;

AObjParent.Write('Json', AJson);

end);

end

end);

AStream.Position := 0;

repeat

AJson.LoadFromStream(AStream, teUtf8);

ShowMessage(AJson.Encode(true));

until AStream.Position = AStream.Size;

finally

ReleaseJson(AJson);

FreeAndNil(AStream);

end;

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