简单java程序在线测评程序

一．前言

　　大家过年好！今年的第一篇博客啊！家里没有网，到处蹭无线！日子过得真纠结！因为毕设的需求，简单写了一个java程序在线测评程序，当然也可以在本地测试。

二．思路

　　首先简单介绍一下思路：

　　1.得到java程序的源代码，不需要导入包。得到源码之后在前面加入”import java.util.*;”

　　2.通过JavaCompiler对象可以帮助我们将java源代码编译成class文件。

　　3.通过DiagnosticCollector对象可以获得编译过程中产生的编译信息。

　　4.通过StandardJavaFileManager对象管理生成的class文件，例如文件的存放位置。

　　5.StringSourceJavaObject对象可以对java源码进行包装并处理。

数据是控制台输入的，所以要重定向System.in(注意保存标准的输入流)；另外程序的输出是到标准的输出流的，为了获得输出结果，我的方法是重定向输出流到ByteArrayOutputStream，然后利用ByteArrayOutputStream构造BufferedReader。

　　6.运行程序，通过java的反射机制，获得main函数的Method对象。

　　7.运行时间的计算: 通过System.currentTimeMillis()方法。

　　8.程序所需内存: 通过Runtime的freeMemory()方法。

　　9.异常信息的获取：StringWriter sw = new StringWriter(); e.printStackTrace(new PrintWriter(sw, true)); sw.toString();

三．问题解决

1. JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); 出现NullPointerException。

　查看部分源码如下：

private static final String[] defaultToolsLocation = { "lib", "tools.jar" };
private Class<?> findSystemToolClass(String toolClassName)throws MalformedURLException, ClassNotFoundException {// try loading class directly, in case tool is on the bootclasspathtry {return Class.forName(toolClassName, false, null);} catch (ClassNotFoundException e) {trace(FINE, e);// if tool not on bootclasspath, look in default tools location (tools.jar)ClassLoader cl = (refToolClassLoader == null ? null : refToolClassLoader.get());if (cl == null) {File file = new File(System.getProperty("java.home"));if (file.getName().equalsIgnoreCase("jre"))file = file.getParentFile();for (String name : defaultToolsLocation)file = new File(file, name);// if tools not found, no point in trying a URLClassLoader// so rethrow the original exception.if (!file.exists())throw e;URL[] urls = { file.toURI().toURL() };trace(FINE, urls[0].toString());cl = URLClassLoader.newInstance(urls);refToolClassLoader = new WeakReference<ClassLoader>(cl);}return Class.forName(toolClassName, false, cl);}
}

打印 System.out.println(System.getProperty("java.home")); 如下：

C:\Program Files (x86)\Java\jre6

defaultToolsLocation = { "lib", "tools.jar" }; 也就是最终到

C:\Program Files (x86)\Java\jre6\lib\tools.jar中寻找tools.jar

然而jre6\lib中没有tools.jar, 而是在C:\Program Files (x86)\Java\jdk\lib中。最直接的办法就是将它复制进去就行了。

2.异常信息的获取。

3.输入流和输出流的重定向。

详细内容请看代码!

四．代码

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.Method;
import java.net.URI;
import java.util.Arrays;
import java.util.regex.Matcher;
import java.util.regex.Pattern;import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;public class CompileAndRunJavaFile {public static void main(String[] args) {StringBuilder code = new StringBuilder();try {BufferedReader br = new BufferedReader(new FileReader(new File("测试程序地址")));String content;while((content = br.readLine()) != null){code.append(content).append("\n");}} catch (Exception e) {e.printStackTrace();}CompileAndRunJavaFile cr = new CompileAndRunJavaFile();cr.compileAndRunJavaFile(code.toString());if(cr.isCompileAndRunOK()) {System.out.println("运行时间: " + cr.getUseTime() + "ms");System.out.println("内存使用: " + cr.getUseMemory() + "kb9");System.out.println("运行结果: \n" + cr.getOutMsg());} else if(cr.isCompilerError()) {System.out.println("编译错误: " + cr.getCE());} else if(cr.isRunningError()) {System.out.println("运行错误: " + cr.getError());}}//编译错误private StringBuilder ce = new StringBuilder();public String getCE(){return ce.toString();}//内存使用private double useMemory = 0.0;public double getUseMemory(){return useMemory;}//运行时间private long useTime = 0;public long getUseTime(){return useTime;}//输出信息private StringBuilder outMsg = new StringBuilder();public String getOutMsg(){return outMsg.toString();}//异常信息private String error = null;public String getError(){return error;}//是否正常编译并运行private boolean isCompileAndRunOK = false; public boolean isCompileAndRunOK(){return isCompileAndRunOK;}//程序的运行时间, 单位：msprivate int limitTime = 2000;//程序所占内存, 单位 ：KBprivate double limitMemory = 256000.0;public void setLimitTime(int limitTime){this.limitTime = limitTime;}public void setLimitMemory(double limitMemory){this.limitMemory = limitMemory;}//是否为编译错误private boolean isCompilerError = false;public boolean isCompilerError(){return isCompilerError;}//是否为运行错误private boolean isRunningError = false;public boolean isRunningError(){return isRunningError;}private static final String className = "Main";private static final String methodName = "main";private String getClassOutput(){//设置class文件的存放位置if(System.getProperty("java.class.path").contains("bin")) return "bin/";else return "./";}private void compileAndRunJavaFile(String code){PrintStream ps = null;FileInputStream fis = null;BufferedReader br = null;//保存标准输出流InputStream stdIn = System.in;//保存标准输入流PrintStream stdOut = System.out;//为源代码导入默认的包code = "import java.util.*;\n" + code;try {JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();// define the diagnostic object, which will be used to save the// diagnostic informationDiagnosticCollector<JavaFileObject> oDiagnosticCollector = new DiagnosticCollector<JavaFileObject>();StandardJavaFileManager fileManager = compiler.getStandardFileManager(oDiagnosticCollector, null, null);// set class output locationfileManager.setLocation(StandardLocation.CLASS_OUTPUT, Arrays.asList(new File[] { new File(getClassOutput()) }));StringSourceJavaObject sourceObject = new CompileAndRunJavaFile.StringSourceJavaObject(className, code);Iterable<? extends JavaFileObject> fileObjects = Arrays.asList(sourceObject);CompilationTask task = compiler.getTask(null, fileManager, oDiagnosticCollector, null, null, fileObjects);boolean result = task.call();if (result) {Runtime runtime = Runtime.getRuntime();Class<?> clazz = Class.forName(className);Method method = clazz.getMethod(methodName, new Class<?>[]{String[].class});//重置输入流， 需要存放数据文件的文件名fis = new FileInputStream(new File("数据文件地址"));System.setIn(fis);//重置输出流，需要获得控制台的输出ByteArrayOutputStream bao = new ByteArrayOutputStream();ps = new PrintStream(bao);System.setOut(ps);long startFreeMemory = runtime.freeMemory();//Java 虚拟机中的空闲内存量//执行时间也是无法知道，因为dos执行java命令，程序无法知道它到底执行到那里了，两个进程，互不了解long startCurrentTime = System.currentTimeMillis();//获取系统当前时间method.invoke(null, new Object[]{null});long endCurrentTime = System.currentTimeMillis();long endFreeMemory = runtime.freeMemory();//内存的使用情况，不是很精确useMemory = (startFreeMemory-endFreeMemory)/1024.0;if(useMemory > limitMemory) throw new Exception("Out Limit Memory!");useTime = endCurrentTime-startCurrentTime;if(useTime > limitTime) throw new Exception("Time Limited!");//获得控制台的输出br = new BufferedReader(new InputStreamReader(new ByteArrayInputStream(bao.toByteArray())));String outc = null;while((outc = br.readLine()) != null)outMsg.append(outc).append("\n");//正常编译并运行isCompileAndRunOK = true;} else {isCompilerError = true;//打印编译的错误信息Pattern p = Pattern.compile("Main.java\\D*(\\d+):", Pattern.DOTALL);for (Diagnostic<? extends JavaFileObject> oDiagnostic : oDiagnosticCollector.getDiagnostics()){/*信息示例：Compiler Error: Main.java:8: 找不到符号符号： 类 Scanner位置： 类 Main*///将行号减1Matcher m = p.matcher("Compiler Error: " + oDiagnostic.getMessage(null));if(m.find()) {ce.append(m.replaceAll("Main.java " + String.valueOf(Integer.valueOf(m.group(1))-1)) + ":").append("\n");} else {ce.append("Compiler Error: " + oDiagnostic.getMessage(null)).append("\n");}}}} catch (Exception e) {isRunningError = true;StringWriter sw = new StringWriter();e.printStackTrace(new PrintWriter(sw, true));Pattern p = Pattern.compile("Main.java\\D*(\\d+)", Pattern.DOTALL);Matcher m = p.matcher(sw.toString());if(m.find()){error = m.replaceAll("Main.java " + String.valueOf(Integer.valueOf(m.group(1))-1) + ":");} else {error = sw.toString();}} finally {//关闭流try {if(fis != null)fis.close();if(ps != null)ps.close();    if(br != null)br.close();} catch (IOException e) {e.printStackTrace();}//恢复输入输出流
            System.setIn(stdIn);System.setOut(stdOut);}}private class StringSourceJavaObject extends SimpleJavaFileObject {private String content = null;public StringSourceJavaObject(String name, String content) {super(URI.create(name.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);this.content = content;}public CharSequence getCharContent(boolean ignoreEncodingErrors) {return content;}}
}

View Code

五．运行结果显示

1.正常运行

运行时间: 16ms

内存使用: 225.5546875kb

运行结果:

5 4 3 2 1

2.编译错误

编译错误: Compiler Error: Main.java 8 找不到符号

符号：类 Scanner

位置：类 Main:

Compiler Error: Main.java 8 找不到符号

符号：类 Scanner

位置：类 Main:

3.运行错误

(1)运行错误: java.lang.reflect.InvocationTargetException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at com.test.CompileAndRunJavaFile.compileAndRunJavaFile(CompileAndRunJavaFile.java:163)

at com.test.CompileAndRunJavaFile.main(CompileAndRunJavaFile.java:44)

Caused by: java.lang.StackOverflowError

at Main.fun(Main.java 4:)

(2)运行错误: java.lang.reflect.InvocationTargetException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at com.test.CompileAndRunJavaFile.compileAndRunJavaFile(CompileAndRunJavaFile.java:163)

at com.test.CompileAndRunJavaFile.main(CompileAndRunJavaFile.java:44)

Caused by: java.lang.ArrayIndexOutOfBoundsException: 6

at Main.main(Main.java 18:)

... 6 more

六．测试程序

public class Main {public static void fun(){fun();}public static void main(String[] args) {Scanner scan = new Scanner(System.in);int n = scan.nextInt();int[] array = new int[n];for(int i=0; i<n; ++i)array[i] = scan.nextInt();for(int i=0; i<n; ++i)System.out.print(array[i] + " ");System.out.println();//array[n+1] = 0;//fun();
    }}