问题
I wrote these 2 lines of code to create a chart using an XYDataset:
final XYDataset dataset = new TimeSeriesCollection(myInfo.getSeries());
JFreeChart timechart = ChartFactory.createTimeSeriesChart(myInfo.getName()
+ " CPU (last 72h)", "", "CPU %", dataset, false, false, false);
These lines created this nice "last 72h" chart:
This is how I added the information to build this chart (this piece of code can run multiple times):
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd H:mm:ss");
Date date = simpleDateFormat.parse(dateAsStringToParse);
Second second = new Second(date);
myInfo.getSeries().addOrUpdate(second, maxValue); // maxValue is an Integer
I want a (seemingly) simple alteration—to "cut" this only to the last 24 hours. I mean to see only the most "recent" 24 hours in the graph, like so (in the picture is a different chart I made using the same technique, but the information exists only for the last 24hrs):
I have looked through the API and could not find an appropriate answer, as I believe this should have some clever but simple solution.
回答1:
Instead of discarding old data, as suggested here, it looks like you want to display a contiguous subset of the data, as if looking through a window. While SlidingCategoryDataset provides this feature for a CategoryDataset, there is no built-in solution for an XYDataset. SlidingXYDataset, seen here, maybe an alternative. In the variation of SliderDemo2 illustrated below, I've added three days of data to a single series with a one day window. I've retained the slider for easy review of earlier values.
static final int COUNT = 3 * 24 * 60;
public static final int WINDOW = 24 * 60;
public static final int FIRST = 2 * 24 * 60;
…
this.slider.setValue(FIRST);
As an aside, note that some classes have moved since the patch was submitted:
import org.jfree.ui.ApplicationFrame;
import org.jfree.ui.RefineryUtilities;
Can't I just use
setMaximumItemAge()?
Not in isolation; addOrUpdate(), et al., calls removeAgedItems(false) before notifying listeners.
I am using
Second.
Threes days of Second data, e.g., would imply setMaximumItemAge(3 * 24 * 60 * 60).
A sliding window might not be available to me since I am saving the chart as a JPEG.
You can pass the desired firstItemIndex as a parameter to the SlidingXYDataset constructor; you can update the index later via setFirstItemIndex() if needed.
来源：https://stackoverflow.com/questions/46121483/how-to-display-only-last-24-hours-from-a-last-72-hours-jfreechart-timeseries