技术教程 编程教程 简单java在线测评程序 正文

简单java在线测评程序

2023-03-10,,

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 bootclasspath

    try {

        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：ms

    private int limitTime = 2000;

    //程序所占内存, 单位 ：KB

    private 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 information

            DiagnosticCollector<JavaFileObject> oDiagnosticCollector = new DiagnosticCollector<JavaFileObject>();

            StandardJavaFileManager fileManager = compiler.getStandardFileManager(oDiagnosticCollector, null, null);

            // set class output location

            fileManager.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1

                    Matcher 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;

        }

    }

}

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:)

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();

    }

}


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