Question

我有一小段代码，每隔五分钟就会截取一次我的桌面屏幕截图 - 这是一个轻松思考的工作，并计算出多少截图，比如facebook ...

然而，我对它占用的内存量感到有点困惑 - 通常它会爬升到200mb的RAM，我确信这是多余的......有人可以告诉我一个合理的方法来减少内存占用或b）为什么它在所有上升？

/**
 * Code modified from code given in http://whileonefork.blogspot.co.uk/2011/02/java-multi-monitor-screenshots.html following a SE question at  
 * http://stackoverflow.com/questions/10042086/screen-capture-in-java-not-capturing-whole-screen and then modified by a code review at http://codereview.stackexchange.com/questions/10783/java-screengrab
 */
package com.tmc.personal;

import java.awt.AWTException;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
import java.util.concurrent.TimeUnit;

import javax.imageio.ImageIO;

class ScreenCapture {

    static int minsBetweenScreenshots = 5;

    public static void main(String args[]) {
        int indexOfPicture = 1000;// should be only used for naming file...
        while (true) {
            takeScreenshot("ScreenCapture" + indexOfPicture++);
            try {
                TimeUnit.MINUTES.sleep(minsBetweenScreenshots);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    //from http://www.coderanch.com/t/409980/java/java/append-file-timestamp
    private  final static String getDateTime()
    {
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd_hh:mm:ss");
        df.setTimeZone(TimeZone.getTimeZone("PST"));
        return df.format(new Date());
    }

    public static void takeScreenshot(String filename) {
        Rectangle allScreenBounds = getAllScreenBounds();
        Robot robot;
        try {
            robot = new Robot();
            BufferedImage screenShot = robot.createScreenCapture(allScreenBounds);
            ImageIO.write(screenShot, "jpg", new File(filename + getDateTime()+ ".jpg"));
        } catch (AWTException e) {
            System.err.println("Something went wrong starting the robot");
            e.printStackTrace();
        } catch (IOException e) {
            System.err.println("Something went wrong writing files");
            e.printStackTrace();
        }
    }

    /**
     * Okay so all we have to do here is find the screen with the lowest x, the
     * screen with the lowest y, the screen with the higtest value of X+ width
     * and the screen with the highest value of Y+height
     * 
     * @return A rectangle that covers the all screens that might be nearby...
     */
    private static Rectangle getAllScreenBounds() {
        Rectangle allScreenBounds = new Rectangle();
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice[] screens = ge.getScreenDevices();

        int farx = 0;
        int fary = 0;
        for (GraphicsDevice screen : screens) {
            Rectangle screenBounds = screen.getDefaultConfiguration().getBounds();
            // finding the one corner
            if (allScreenBounds.x > screenBounds.x) {
                allScreenBounds.x = screenBounds.x;
            }
            if (allScreenBounds.y > screenBounds.y) {
                allScreenBounds.y = screenBounds.y;
            }
            // finding the other corner
            if (farx < (screenBounds.x + screenBounds.width)) {
                farx = screenBounds.x + screenBounds.width;
            }
            if (fary < (screenBounds.y + screenBounds.height)) {
                fary = screenBounds.y + screenBounds.height;
            }
            allScreenBounds.width = farx - allScreenBounds.x;
            allScreenBounds.height = fary - allScreenBounds.y;
        }
        return allScreenBounds;
    }
}

Answer 1

其他答案是正确的，Java将使用尽可能多的内存，此时它将进行垃圾收集。要解决此问题，可以在JVM设置中指定较小的最大堆大小。您可以使用-Xmx设置执行此操作。例如，如果您认为只需要32MB，请将其运行为：

java -Xmx32M [your main class or jar here]

您的程序堆（非堆栈内存）永远不会超过32MB，但如果它需要多于一次（并且您需要配置文件），它将崩溃。我没有看到你的程序有任何明显的泄漏（假设ImageIO不需要任何清理），所以我认为你会没事的。

Answer 2

对于现代计算机，200MB并不是过多的内存。如果您正在创建和丢弃大量对象，JVM将让堆增长一段时间，这样您的程序就不会陷入垃圾回收的困境。让你的程序运行几个小时，然后检查你是否认为有问题。

Answer 3

JVM垃圾收集器最终会清除你的内存堆。要手动清除堆调用Runtime.getRuntime().gc();，但我不建议每5分钟执行一次。

为什么这个Java程序占用了这么多内存？

3 个答案: