我最近注意到，自从我更新到 Java 7 后，我的代码的特定部分运行速度明显变慢。令人惊讶的是，Java 7 在全球范围内都比 Java 6 快。
该程序非常大，但我成功提取了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，您会发现Java 7 比 Java 6 慢大约 7-8 倍！！！
这是代码（不要费心去理解它的作用，它只是真实代码的抽象，因此没有任何意义）。它基本上是一个解析字符串以格式化它的某些部分的代码：
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();
}
}
}
}
}
在我的计算机上，如果我使用 Java 6 运行它，平均运行时间为60 毫秒。
如果我使用 Java 7 运行它，则需要460 毫秒。
我是唯一注意到这一点的人吗？谢谢，
编辑：这是证明错误方法是 Java 7 中的 DefaultStyledDocument.setCharacateAttributes()的新程序：
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
有什么方法可以让它在 Java 7 中像在 Java 6 中一样快地工作？谢谢，
编辑：这是修复性能的解决方法。Java 7 的问题（我在insertString()和remove()上做了）：
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);
}