[BUG] 避免字符串和MetricNode对象的转换,减少内存占用

[brucelwl]

Sentinel/sentinel-core/src/main/java/com/alibaba/csp/sentinel/node/metric/MetricsReader.java

Lines 54 to 56 in 195150b

	while ((line = reader.readLine()) != null) {
	MetricNode node = MetricNode.fromFatString(line);
	long currentSecond = node.getTimestamp() / 1000;

55行没必要为了获取时间戳而将字符串转成MetricNode对象, 直接通过字符串截取就行,

int timestampIndex = s.indexOf("|");
String timestamp = Long.parseLong(s.substring(0, timestampIndex));

Sentinel/sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/command/handler/SendMetricCommandHandler.java

Lines 97 to 100 in 195150b

	StringBuilder sb = new StringBuilder();
	for (MetricNode node : list) {
	sb.append(node.toThinString()).append("\n");
	}

SendMetricCommandHandler中为了得到ThinString, 又将MetricNode转成字符串, MetricNode成了冗余转换, 会增加内存占用
不如直接采用FatString字符串分割

int timestampIndex = s.indexOf("|");
String timestamp = s.substring(0, timestampIndex);

int i = s.indexOf("|", timestampIndex + 20);
String metric = s.substring(i);

System.out.println(timestamp + metric);