首先，您应该停止序列化到中间string而是直接序列化到HttpResponse.OutputStream，使用以下简单方法：
public static class JsonExtensions
{
public static void SerializeToStream(object value, System.Web.HttpResponse response, JsonSerializerSettings settings = null)
{
if (response == null)
throw new ArgumentNullException("response");
SerializeToStream(value, response.OutputStream, settings);
}
public static void SerializeToStream(object value, TextWriter writer, JsonSerializerSettings settings = null)
{
if (writer == null)
throw new ArgumentNullException("writer");
var serializer = JsonSerializer.CreateDefault(settings);
serializer.Serialize(writer, value);
}
public static void SerializeToStream(object value, Stream stream, JsonSerializerSettings settings = null)
{
if (stream == null)
throw new ArgumentNullException("stream");
using (var writer = new StreamWriter(stream))
{
SerializeToStream(value, writer, settings);
}
}
}
由于大字符串需要大连续的底层的内存块char数组，这就是你首先会耗尽内存的地方。另请参阅 Json.NET性能技巧
为了最大限度地减少内存使用和分配的对象数量，Json.NET 支持直接序列化和反序列化到流。在处理大小大于 85kb 的 JSON 文档时，一次读取或写入一段 JSON，而不是将整个 JSON 字符串加载到内存中，这一点尤其重要，以避免 JSON 字符串最终出现在大型对象堆中。
接下来，请务必将所有一次性物品包裹在一个using语句，如下图所示。
这可能会解决您的问题，但如果没有，您可以序列化IDataReader使用以下命令转换为 JSONJsonConverter:
public class DataReaderConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return typeof(IDataReader).IsAssignableFrom(objectType);
}
public override bool CanRead { get { return false; } }
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var reader = (IDataReader)value;
writer.WriteStartArray();
while (reader.Read())
{
writer.WriteStartObject();
for (int i = 0; i < reader.FieldCount; i++)
{
writer.WritePropertyName(reader.GetName(i));
if (reader.IsDBNull(i))
writer.WriteNull();
else
serializer.Serialize(writer, reader[i]);
}
writer.WriteEndObject();
}
writer.WriteEndArray();
}
}
然后序列化为stream，如下：
public static class ExcelExtensions
{
private static string GetExcelConnectionString(string path)
{
string connectionString = string.Empty;
if (path.EndsWith(".xls"))
{
connectionString = String.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;
Data Source={0};
Extended Properties=""Excel 8.0;HDR=YES;IMEX=1""", path);
}
else if (path.EndsWith(".xlsx"))
{
connectionString = String.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;
Data Source={0};
Extended Properties=""Excel 12.0 Xml;HDR=YES;IMEX=1""", path);
}
return connectionString;
}
public static string SerializeJsonToString(string path, string workSheetName, JsonSerializerSettings settings = null)
{
using (var writer = new StringWriter())
{
SerializeJsonToStream(path, workSheetName, writer, settings);
return writer.ToString();
}
}
public static void SerializeJsonToStream(string path, string workSheetName, Stream stream, JsonSerializerSettings settings = null)
{
using (var writer = new StreamWriter(stream))
SerializeJsonToStream(path, workSheetName, writer, settings);
}
public static void SerializeJsonToStream(string path, string workSheetName, TextWriter writer, JsonSerializerSettings settings = null)
{
settings = settings ?? new JsonSerializerSettings();
var converter = new DataReaderConverter();
settings.Converters.Add(converter);
try
{
string connectionString = GetExcelConnectionString(path);
DbProviderFactory factory = DbProviderFactories.GetFactory("System.Data.OleDb");
using (OleDbConnection conn = new OleDbConnection(connectionString))
{
conn.Open();
using (DbCommand selectCommand = factory.CreateCommand())
{
selectCommand.CommandText = String.Format("SELECT * FROM [{0}]", workSheetName);
selectCommand.Connection = conn;
using (var reader = selectCommand.ExecuteReader())
{
JsonExtensions.SerializeToStream(reader, writer, settings);
}
}
}
}
finally
{
settings.Converters.Remove(converter);
}
}
}
注意-经过轻微测试。在将其投入生产之前，请务必根据现有方法对其进行单元测试！对于我使用的转换器代码DataReader 的 JSON 序列化作为灵感。
Update
我的转换器发出的 JSON 结构与DataTableConverterJson.NET 的。因此你将能够反序列化为DataTable自动使用 Json.NET。如果您喜欢更紧凑的格式，您可以定义自己的格式，例如：
{
"columns": [
"Name 1",
"Name 2"
],
"rows": [
[
"value 11",
"value 12"
],
[
"value 21",
"value 22"
]
]
}
他们创建了以下转换器：
public class DataReaderArrayConverter : JsonConverter
{
public override bool CanConvert(Type objectType)
{
return typeof(IDataReader).IsAssignableFrom(objectType);
}
public override bool CanRead { get { return false; } }
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
throw new NotImplementedException();
}
static string[] GetFieldNames(IDataReader reader)
{
var fieldNames = new string[reader.FieldCount];
for (int i = 0; i < reader.FieldCount; i++)
fieldNames[i] = reader.GetName(i);
return fieldNames;
}
static void ValidateFieldNames(IDataReader reader, string[] fieldNames)
{
if (reader.FieldCount != fieldNames.Length)
throw new InvalidOperationException("Unequal record lengths");
for (int i = 0; i < reader.FieldCount; i++)
if (fieldNames[i] != reader.GetName(i))
throw new InvalidOperationException(string.Format("Field names at index {0} differ: \"{1}\" vs \"{2}\"", i, fieldNames[i], reader.GetName(i)));
}
const string columnsName = "columns";
const string rowsName = "rows";
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
var reader = (IDataReader)value;
writer.WriteStartObject();
string[] fieldNames = null;
while (reader.Read())
{
if (fieldNames == null)
{
writer.WritePropertyName(columnsName);
fieldNames = GetFieldNames(reader);
serializer.Serialize(writer, fieldNames);
writer.WritePropertyName(rowsName);
writer.WriteStartArray();
}
else
{
ValidateFieldNames(reader, fieldNames);
}
writer.WriteStartArray();
for (int i = 0; i < reader.FieldCount; i++)
{
if (reader.IsDBNull(i))
writer.WriteNull();
else
serializer.Serialize(writer, reader[i]);
}
writer.WriteEndArray();
}
if (fieldNames != null)
{
writer.WriteEndArray();
}
writer.WriteEndObject();
}
}
当然，您需要在客户端创建自己的反序列化转换器。
或者，您可以考虑压缩您的回复。我从未尝试过，但是看看HttpWebRequest 和 GZip Http 响应 and ASP.NET GZip 编码注意事项.
