我最近注意到，自从我更新到Java 7以来，我的代码的一个特定部分运行速度明显变慢。令人惊讶的是Java 7的速度比Java 6快。
该程序非常庞大，但我成功地提取了一个可重现的代码来演示java 7如何比Java 6慢。
如果您使用Java 6和Java 7运行完全相同的代码，您会看到 Java 7比Java 6慢大约7-8倍 !!!
这是代码（不要试图理解它的作用，它只是来自真实代码的摘要，因此并没有真正有意义）。它基本上是一个解析字符串以格式化其中某些部分的代码：
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Window;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
public class CPerfJava7 extends JFrame {
private static final long serialVersionUID = 1L;
// +==============================================================+
// | Attributes |
// +==============================================================+
JPanel mainPanel;
public CPseudoHtmlDocument docu;
private static long totalTime = 0;
// +==============================================================+
// | Constructors |
// +==============================================================+
public CPerfJava7() {
super("PerfJava7");
docu = new CPseudoHtmlDocument();
mainPanel = new JPanel(new BorderLayout());
JTextPane textPane = new JTextPane();
textPane.setDocument(docu);
textPane.setText("testcase one\ndo program breakfast meal\ndo program time\ndo program portion size - 1/4 of the cup\nIt was easy to set up the time and portion size as directed in the manual\n\ndo collect kibbles from the bowl and measure the breakfast portion\ncheck the portion dispensed 1/4 cup of kibbles \nActual result - it was less than 1/4 cup. The wheel that rotates and dispenses\n the kibbles might haven't rotated completely.\n\ntestcase two\ndo program lunch meal\ndo program time\ndo leave the portion size the same - 1/4 of the cup\n\ncheck the portion dispensed 1/4 cup of kibbles\n do collect kibbles from the bowl and measure the lunch portion\nActual result was 1/20 of the cup, the wheel dispenser hardly released any kibbles\n\ntestcase three\n\ndo program dinner meal\ndo program time\ndo leave the portion size the same - 1/4 of the cup\n\ncheck the portion dispensed 1/4 cup of kibbles\n do collect kibbles from the bowl and measure the dinner portion\nActual result was less than 1/4 cup\n\nWhy was the middle meal the smallest? Is lunch always the smallest?\nTo prove this hypothesis, repeat first three test cases again.\n\ntestcase four\ndo repeat test case one\nActual result - it was less 1/4 and the portion was dispensed in two increments.\n\ntestcase five\ndo repeat test case two\nActual result - 1/8 of the cup.\n\ntestcase six\ndo repeat test case three\nActual result - 1/2 cup! The wheel rotated almost twice. It looked like all\n kibbles which were not dispensed previously, got released.\n Lunch was still the smallest meal, but the dinner portion was twice of the size\n.All three tests must be repeated again.\n\ntestcase seven\ndo repeat test case one\nActual result - 1/4 of the cup. Great!\n\ntestcase eight\ndo repeat test case two\nActual result - 1/4 of the cup! It works perfectly! Why?\n\ntestcase nine\ndo repeat test case three\nActual result - 1/6, so the third meal was less than it should be. Is this size of the portion hard to dispense correctly? Let's try 1/2 of the cup\n\ntestcase ten\ndo program breakfast meal\ndo program time\ndo program 1/2 of the cup\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/2 of the cup. Excellent. The wheel rotated twice as designed. In a minute it added 1/4 of the cup.\n\ntestcase eleven\ndo program lunch meal\ndo program time\ndo leave the portion size the same\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/3 of the cup. Lunch is smaller again.\n\testcase twelve\ndo program dinner meal\ndo program time\ndo leave the portion size the same - 1/2 of the cup\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/2, the portion was dispensed in 2 increments with the interval. As there is no consistency again, let test this portion size one more time.\n \ntestcase thirteen\ndo repeat test case ten\ncheck the amount of kibbles is 1/2 of the cup\nActual result - a bit less than 1/2\n\n\ntestcase fourteen\ndo repeat test case eleven\ncheck the portion size is 1/2 of the cup\nActual result - a bit more than 1/2. This portion size looks more stable. The lunch isn't the smallest anymore.\n\ntestcase fiftee\ndo repeat test case twelve\ncheck portion size is 1/2 of the cup\nActual result - is l/2, a bit less of the exact amount. All three meals were served with almost correct portion size.\n\n\n- \n\n\n");
mainPanel.add(new JScrollPane(textPane), BorderLayout.CENTER);
setContentPane(mainPanel);
}
public static void main(String[] args) {
CPerfJava7 frame;
WindowListener exitListener = new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
Window window = e.getWindow();
window.setVisible(false);
window.dispose();
System.exit(0);
}
};
frame = new CPerfJava7();
frame.addWindowListener(exitListener);
frame.setPreferredSize(new Dimension(600, 400));
frame.pack();
frame.setVisible(true);
try {
// run it to warm it up
frame.docu.doParse();
frame.docu.doParse();
frame.docu.doParse();
frame.docu.doParse();
frame.docu.doParse();
frame.docu.doParse();
// then do real measures
totalTime = 0;
for (int k=0; k<50; k++) {
frame.docu.doParse();
}
System.err.println(" AVERAGE = " + (totalTime/50));
} catch (Exception e) {
e.printStackTrace();
}
}
/*
+----------------------------------------------------------------------+
| Class: CPseudoHtmlDocument |
+----------------------------------------------------------------------+
*/
@SuppressWarnings("serial")
public class CPseudoHtmlDocument extends DefaultStyledDocument {
// +==============================================================+
// | Attribute(s) |
// +==============================================================+
private final SimpleAttributeSet attrNormal = new SimpleAttributeSet();
private final SimpleAttributeSet attrSpecial = new SimpleAttributeSet();
private final SimpleAttributeSet attrDefault = new SimpleAttributeSet();
private int currentPos = 0;
// +==============================================================+
// | Constructor(s) |
// +==============================================================+
public CPseudoHtmlDocument() {
StyleConstants.setForeground(attrSpecial, Color.decode("0xC71D15"));StyleConstants.setBold(attrSpecial, true);
StyleConstants.setForeground(attrDefault, new Color(150, 150, 0));
StyleConstants.setBold(attrDefault, true);
}
// +==============================================================+
// | Method(s) |
// +==============================================================+
public long getCurrentTimeMillis() {
Calendar now = Calendar.getInstance();
return now.getTimeInMillis();
}
public String getCurrentLogTime() {
Calendar now = Calendar.getInstance();
return calendarToPreciseTimeOfTheDay(now);
}
public String calendarToPreciseTimeOfTheDay (Calendar calendar) {
SimpleDateFormat localSimpleDateFormat = new SimpleDateFormat("HH:mm:ss.S");
return localSimpleDateFormat.format(calendar.getTime());
}
private void doParse() {
long before = getCurrentTimeMillis();
setCharacterAttributes(0, 3260, new SimpleAttributeSet(), true); // reset all the text to review (including the rewinded part) with normal attribute
for (int i = 0; i <= 3260; i++) {
currentPos = i;
checkForKeyword(true);
}
long after = getCurrentTimeMillis();
totalTime += (after-before);
System.err.println(" -> time to parse: " + (after-before) + " ms");
}
private void checkForKeyword(boolean insert) {
int preceedingStartTag, nextStopTag, preceedingPercentTag, nextPercentTag, preceedingSpace, nextSpace;
char currentChar = ' ';
try {
currentChar = this.getText(currentPos, 1).charAt(0);
} catch (BadLocationException e1) {
}
if (currentChar == '[') {
nextStopTag = getNextStop(currentPos+1, true);
setStyle(currentPos, nextStopTag); // check if this is a [xxx] we need to highlight
} else if (currentChar == ']') {
preceedingStartTag = getPreceedingStart(currentPos-1, true); // returns -1 if not found or another [, ], \n or space found first
setStyle(preceedingStartTag, currentPos); // check if this is a [xxx] we need to highlight
} else if (currentChar == '%') {
nextPercentTag = getNextPercent(currentPos+1, true); // returns -1 if not found or \n or space found first
if (nextPercentTag >= 0) {
// removed code
}
} else {
// [xxx]
preceedingStartTag = getPreceedingStart(currentPos-1, true); // returns -1 if not found or another ], \n or space found first
nextStopTag = getNextStop(currentPos, true); // returns -1 if not found or another [, \n or space found first
if (preceedingStartTag >=0 && nextStopTag >=0) {
setStyle(preceedingStartTag, nextStopTag);
}
// PARAMS
preceedingPercentTag = getPreceedingPercent(currentPos-1, true); // returns -1 if not found or another [, ], \n or space found first
nextPercentTag = getNextPercent(currentPos, true); // returns -1 if not found or another [, ], \n or space found first
if (preceedingPercentTag >=0 && nextPercentTag >=0) {
}
// PDNL
preceedingSpace = getPreceedingSpace(currentPos-1, true); // returns -1 if another [, ] or % found first, 0 if not found
nextSpace = getNextSpace(currentPos, true); // returns -1 if not found or another [, ] or % found first, length-1 if not found
if (preceedingSpace >=0 && nextSpace >=0) {
if (preceedingSpace == 0) preceedingSpace--; // keyword at the very beginning of the text
setStyle(preceedingSpace+1, nextSpace-1);
}
}
}
private int getPreceedingStart(int offset, boolean strict) {
while (offset >= 0) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == '[') {
return offset;
} else if (charAt == ']' || charAt == '%' || charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
e.printStackTrace();
}
offset--;
}
if (strict)
return -1;
else
return 0;
}
private int getNextStop(int offset, boolean strict) {
while (true) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == ']') {
return offset;
} else if (charAt == '[' || charAt == '%' || charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
if (strict)
return -1;
else
return offset-1;
}
offset++;
}
}
private int getPreceedingPercent(int offset, boolean strict) {
while (offset >= 0) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == '%') {
return offset;
} else if (charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
e.printStackTrace();
}
offset--;
}
if (strict)
return -1;
else
return 0;
}
private int getNextPercent(int offset, boolean strict) {
while (true) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == '%') {
return offset;
} else if (charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
if (strict)
return -1;
else
return offset;
}
offset++;
}
}
private int getPreceedingSpace(int offset, boolean strict) {
while (offset >= 0) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
return offset;
} else if (charAt == '%' || charAt == '[' || charAt == ']') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
e.printStackTrace();
}
offset--;
}
return 0;
}
private int getNextSpace(int offset, boolean strict) {
while (true) {
try {
char charAt = this.getText(offset, 1).charAt(0);
if (charAt == ' ' || charAt == '\n' || charAt == '\r' || charAt == '\t') {
return offset;
} else if (charAt == '%' || charAt == '[' || charAt == ']') {
if (strict)
return -1;
}
} catch (BadLocationException e) {
return offset-1;
}
offset++;
}
}
private void setStyle(int startTag, int stopTag) {
if (startTag >= 0 && stopTag > 0 && stopTag > startTag) {
int tagLength = stopTag-startTag+1;
try {
String tag = this.getText(startTag, tagLength);
String s = tag.trim()/*.toLowerCase()*/;
if (s.equals("testcase") || s.equals("do") || s.equals("check") || s.equals("and")) {
setCharacterAttributes(startTag, tagLength, attrSpecial, true);
} else {
setCharacterAttributes(startTag, tagLength, attrNormal, true);
}
} catch (BadLocationException e) {
e.printStackTrace();
}
}
}
}
}
如果我在Java 6上运行它，在计算机上运行它的平均时间 60ms 。
如果我使用Java 7运行它将需要 460ms 。
我是唯一注意到这一点的人吗？ 谢谢，
编辑：这是新程序证明错误的方法是Java 7中的DefaultStyledDocument.setCharacaterAttributes（）：
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Window;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.util.Calendar;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
public class CPerfJava7_justSetCharacterAttributes extends JFrame {
private static final long serialVersionUID = 1L;
// +==============================================================+
// | Attributes |
// +==============================================================+
JPanel mainPanel;
public CPseudoHtmlDocument docu;
// +==============================================================+
// | Constructors |
// +==============================================================+
public CPerfJava7_justSetCharacterAttributes() {
super("PerfJava7");
docu = new CPseudoHtmlDocument();
mainPanel = new JPanel(new BorderLayout());
JTextPane textPane = new JTextPane();
textPane.setDocument(docu);
textPane.setText("testcase one\ndo program breakfast meal\ndo program time\ndo program portion size - 1/4 of the cup\nIt was easy to set up the time and portion size as directed in the manual\n\ndo collect kibbles from the bowl and measure the breakfast portion\ncheck the portion dispensed 1/4 cup of kibbles \nActual result - it was less than 1/4 cup. The wheel that rotates and dispenses\n the kibbles might haven't rotated completely.\n\ntestcase two\ndo program lunch meal\ndo program time\ndo leave the portion size the same - 1/4 of the cup\n\ncheck the portion dispensed 1/4 cup of kibbles\n do collect kibbles from the bowl and measure the lunch portion\nActual result was 1/20 of the cup, the wheel dispenser hardly released any kibbles\n\ntestcase three\n\ndo program dinner meal\ndo program time\ndo leave the portion size the same - 1/4 of the cup\n\ncheck the portion dispensed 1/4 cup of kibbles\n do collect kibbles from the bowl and measure the dinner portion\nActual result was less than 1/4 cup\n\nWhy was the middle meal the smallest? Is lunch always the smallest?\nTo prove this hypothesis, repeat first three test cases again.\n\ntestcase four\ndo repeat test case one\nActual result - it was less 1/4 and the portion was dispensed in two increments.\n\ntestcase five\ndo repeat test case two\nActual result - 1/8 of the cup.\n\ntestcase six\ndo repeat test case three\nActual result - 1/2 cup! The wheel rotated almost twice. It looked like all\n kibbles which were not dispensed previously, got released.\n Lunch was still the smallest meal, but the dinner portion was twice of the size\n.All three tests must be repeated again.\n\ntestcase seven\ndo repeat test case one\nActual result - 1/4 of the cup. Great!\n\ntestcase eight\ndo repeat test case two\nActual result - 1/4 of the cup! It works perfectly! Why?\n\ntestcase nine\ndo repeat test case three\nActual result - 1/6, so the third meal was less than it should be. Is this size of the portion hard to dispense correctly? Let's try 1/2 of the cup\n\ntestcase ten\ndo program breakfast meal\ndo program time\ndo program 1/2 of the cup\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/2 of the cup. Excellent. The wheel rotated twice as designed. In a minute it added 1/4 of the cup.\n\ntestcase eleven\ndo program lunch meal\ndo program time\ndo leave the portion size the same\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/3 of the cup. Lunch is smaller again.\n\testcase twelve\ndo program dinner meal\ndo program time\ndo leave the portion size the same - 1/2 of the cup\ncheck the amount of kibbles dispensed is 1/2 of the cup\nActual result - 1/2, the portion was dispensed in 2 increments with the interval. As there is no consistency again, let test this portion size one more time.\n \ntestcase thirteen\ndo repeat test case ten\ncheck the amount of kibbles is 1/2 of the cup\nActual result - a bit less than 1/2\n\n\ntestcase fourteen\ndo repeat test case eleven\ncheck the portion size is 1/2 of the cup\nActual result - a bit more than 1/2. This portion size looks more stable. The lunch isn't the smallest anymore.\n\ntestcase fiftee\ndo repeat test case twelve\ncheck portion size is 1/2 of the cup\nActual result - is l/2, a bit less of the exact amount. All three meals were served with almost correct portion size.\n\n\n- \n\n\n");
mainPanel.add(new JScrollPane(textPane), BorderLayout.CENTER);
setContentPane(mainPanel);
}
public static void main(String[] args) {
CPerfJava7_justSetCharacterAttributes frame;
WindowListener exitListener = new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
Window window = e.getWindow();
window.setVisible(false);
window.dispose();
System.exit(0);
}
};
frame = new CPerfJava7_justSetCharacterAttributes();
frame.addWindowListener(exitListener);
frame.setPreferredSize(new Dimension(600, 400));
frame.pack();
frame.setVisible(true);
try {
// run it to warm it up
frame.docu.doParse();
} catch (Exception e) {
e.printStackTrace();
}
}
/*
+----------------------------------------------------------------------+
| Class: CPseudoHtmlDocument |
+----------------------------------------------------------------------+
*/
@SuppressWarnings("serial")
public class CPseudoHtmlDocument extends DefaultStyledDocument {
private final SimpleAttributeSet attrDefault = new SimpleAttributeSet();
public CPseudoHtmlDocument() {
StyleConstants.setForeground(attrDefault, new Color(150, 150, 0));
StyleConstants.setBold(attrDefault, true);
}
public long getCurrentTimeMillis() {
Calendar now = Calendar.getInstance();
return now.getTimeInMillis();
}
private void doParse() {
long before = getCurrentTimeMillis();
for (int k=0; k<5; k++) {
for (int i = 0; i <= 3260; i+=1) {
setStyle(i, i+1);
}
}
long after = getCurrentTimeMillis();
System.err.println(" -> time to parse: " + (after-before) + " ms");
}
private void setStyle(int startTag, int stopTag) {
int tagLength = stopTag-startTag+1;
setCharacterAttributes(startTag, tagLength, attrDefault, true);
}
}
}
在我的电脑上：
Java 6：~1秒
Java 7：~4.5秒
是否可以像Java 6一样快速地在Java 7中使用它？ 谢谢，
编辑：这是修复此问题的解决方法。 Java 7的问题（我是在 insertString（）和 remove（）上完成的）：
public void remove(int offset, int length) throws BadLocationException {
// start by removing normally the string using the default styled document
try {
super.remove(offset, length);
} catch (Exception e) {
e.printStackTrace();
}
int caretPosition = textPane.getCaretPosition();
textPane.setDocument(new DefaultStyledDocument());
// DO HERE THE TIME-CONSUMING TASKS THAT APPLY SOME STYLES ON THE CURRENT DOCUMENT
textPane.setDocument(this);
textPane.setCaretPosition(caretPosition);
}
答案 0 :(得分：4)
我认为问题不是文档而是视图结构布局的差异。
尝试创建一个没有JTextPane的Document并应用所有样式。
在java7中引入了断点计算，以定义视图可以包装的位置。布局中存在错误，请参阅Strange text wrapping with styled text in JTextPane with Java 7
猜测简单布局会发生同样的情况。
您可以尝试使用ParagraphView和LabelView视图，并查看布局中的不同更改如何极大地改变性能。
答案 1 :(得分：2)
正如this link所建议的那样，用getHighlighter（）。addHighlight（）替换setCharacterAttributes可能会很有趣。它可能更快，也许Java版本之间的差异会大大减少。我无法测试它，因为它需要对代码进行太多更改。
答案 2 :(得分：0)
我看到给定的代码片段使用的是SimpleDateFormat。 Calendar.GetInstance和SimpleDateFormat是Java 7中已知的性能问题，特别是在运行多个线程时。尝试将SimpleDateFormat更改为JodaTime或更改您的代码以使用TimeStamp（长格式）并测试一次。