需求：要实现一个web网页中输入java代码，然后能知道编译结果以及执行结果
类似于菜鸟java在线工具的效果：https://c.runoob.com/compile/10
刚开始从什么概念都没有到最后封装成一个完整的工具类，中间查阅了很多资料才了解其中的概念以及流程，参考文献在文章最后面。
重点需要了解的概念是：
JavaFileManage、JavaFileObject
推荐先看这篇文章：http://blog.onlycatch.com/post/java-Compiler-API
这里是一个封装的demo代码：
package compiler.mydemo;
import javax.tools.Diagnostic;
import javax.tools.DiagnosticCollector;
import javax.tools.FileObject;
import javax.tools.ForwardingJavaFileManager;
import javax.tools.JavaCompiler;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URI;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* Create by andy on 2018-12-06 21:25
*/
public class CustomStringJavaCompiler {
//类全名
private String fullClassName;
private String sourceCode;
//存放编译之后的字节码(key:类全名,value:编译之后输出的字节码)
private Map javaFileObjectMap = new ConcurrentHashMap<>();
//获取java的编译器
private JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
//存放编译过程中输出的信息
private DiagnosticCollector diagnosticsCollector = new DiagnosticCollector<>();
//执行结果（控制台输出的内容）
private String runResult;
//编译耗时(单位ms)
private long compilerTakeTime;
//运行耗时(单位ms)
private long runTakeTime;
public CustomStringJavaCompiler(String sourceCode) {
this.sourceCode = sourceCode;
this.fullClassName = getFullClassName(sourceCode);
}
/**
* 编译字符串源代码,编译失败在 diagnosticsCollector 中获取提示信息
*
* @return true:编译成功 false:编译失败
*/
public boolean compiler() {
long startTime = System.currentTimeMillis();
//标准的内容管理器,更换成自己的实现，覆盖部分方法
StandardJavaFileManager standardFileManager = compiler.getStandardFileManager(diagnosticsCollector, null, null);
JavaFileManager javaFileManager = new StringJavaFileManage(standardFileManager);
//构造源代码对象
JavaFileObject javaFileObject = new StringJavaFileObject(fullClassName, sourceCode);
//获取一个编译任务
JavaCompiler.CompilationTask task = compiler.getTask(null, javaFileManager, diagnosticsCollector, null, null, Arrays.asList(javaFileObject));
//设置编译耗时
compilerTakeTime = System.currentTimeMillis() - startTime;
return task.call();
}
/**
* 执行main方法，重定向System.out.print
*/
public void runMainMethod() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException, UnsupportedEncodingException {
PrintStream out = System.out;
try {
long startTime = System.currentTimeMillis();
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
PrintStream printStream = new PrintStream(outputStream);
//PrintStream PrintStream = new PrintStream("/Users/andy/Desktop/tem.sql"); //输出到文件
System.setOut(printStream);
StringClassLoader scl = new StringClassLoader();
Class aClass = scl.findClass(fullClassName);
Method main = aClass.getMethod("main", String[].class);
Object[] pars = new Object[]{1};
pars[0] = new String[]{};
main.invoke(null, pars); //调用main方法
//设置运行耗时
runTakeTime = System.currentTimeMillis() - startTime;
//设置打印输出的内容
runResult = new String(outputStream.toByteArray(), "utf-8");
} finally {
//还原默认打印的对象
System.setOut(out);
}
}
/**
* @return 编译信息(错误 警告)
*/
public String getCompilerMessage() {
StringBuilder sb = new StringBuilder();
List> diagnostics = diagnosticsCollector.getDiagnostics();
for (Diagnostic diagnostic : diagnostics) {
sb.append(diagnostic.toString()).append("\r\n");
}
return sb.toString();
}
/**
* @return 控制台打印的信息
*/
public String getRunResult() {
return runResult;
}
public long getCompilerTakeTime() {
return compilerTakeTime;
}
public long getRunTakeTime() {
return runTakeTime;
}
/**
* 获取类的全名称
*
* @param sourceCode 源码
* @return 类的全名称
*/
public static String getFullClassName(String sourceCode) {
String className = "";
Pattern pattern = Pattern.compile("package\\s+\\S+\\s*;");
Matcher matcher = pattern.matcher(sourceCode);
if (matcher.find()) {
className = matcher.group().replaceFirst("package", "").replace(";", "").trim() + ".";
}
pattern = Pattern.compile("class\\s+\\S+\\s+\\{");
matcher = pattern.matcher(sourceCode);
if (matcher.find()) {
className += matcher.group().replaceFirst("class", "").replace("{", "").trim();
}
return className;
}
/**
* 自定义一个字符串的源码对象
*/
private class StringJavaFileObject extends SimpleJavaFileObject {
//等待编译的源码字段
private String contents;
//java源代码 => StringJavaFileObject对象 的时候使用
public StringJavaFileObject(String className, String contents) {
super(URI.create("string:///" + className.replaceAll("\\.", "/") + Kind.SOURCE.extension), Kind.SOURCE);
this.contents = contents;
}
//字符串源码会调用该方法
@Override
public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
return contents;
}
}
/**
* 自定义一个编译之后的字节码对象
*/
private class ByteJavaFileObject extends SimpleJavaFileObject {
//存放编译后的字节码
private ByteArrayOutputStream outPutStream;
public ByteJavaFileObject(String className, Kind kind) {
super(URI.create("string:///" + className.replaceAll("\\.", "/") + Kind.SOURCE.extension), kind);
}
//StringJavaFileManage 编译之后的字节码输出会调用该方法（把字节码输出到outputStream）
@Override
public OutputStream openOutputStream() {
outPutStream = new ByteArrayOutputStream();
return outPutStream;
}
//在类加载器加载的时候需要用到
public byte[] getCompiledBytes() {
return outPutStream.toByteArray();
}
}
/**
* 自定义一个JavaFileManage来控制编译之后字节码的输出位置
*/
private class StringJavaFileManage extends ForwardingJavaFileManager {
StringJavaFileManage(JavaFileManager fileManager) {
super(fileManager);
}
//获取输出的文件对象，它表示给定位置处指定类型的指定类。
@Override
public JavaFileObject getJavaFileForOutput(Location location, String className, JavaFileObject.Kind kind, FileObject sibling) throws IOException {
ByteJavaFileObject javaFileObject = new ByteJavaFileObject(className, kind);
javaFileObjectMap.put(className, javaFileObject);
return javaFileObject;
}
}
/**
* 自定义类加载器, 用来加载动态的字节码
*/
private class StringClassLoader extends ClassLoader {
@Override
protected Class findClass(String name) throws ClassNotFoundException {
ByteJavaFileObject fileObject = javaFileObjectMap.get(name);
if (fileObject != null) {
byte[] bytes = fileObject.getCompiledBytes();
return defineClass(name, bytes, 0, bytes.length);
}
try {
return ClassLoader.getSystemClassLoader().loadClass(name);
} catch (Exception e) {
return super.findClass(name);
}
}
}
}
测试代码：
package compiler.mydemo;
/**
* Create by andy on 2018-12-06 15:21
*/
public class Test1 {
public static void main(String[] args) {
String code = "public class HelloWorld {\n" +
" public static void main(String []args) {\n" +
"\t\tfor(int i=0; i < 1; i++){\n" +
"\t\t\t System.out.println(\"Hello World!\");\n" +
"\t\t}\n" +
" }\n" +
"}";
CustomStringJavaCompiler compiler = new CustomStringJavaCompiler(code);
boolean res = compiler.compiler();
if (res) {
System.out.println("编译成功");
System.out.println("compilerTakeTime：" + compiler.getCompilerTakeTime());
try {
compiler.runMainMethod();
System.out.println("runTakeTime：" + compiler.getRunTakeTime());
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(compiler.getRunResult());
System.out.println("诊断信息：" + compiler.getCompilerMessage());
} else {
System.out.println("编译失败");
System.out.println(compiler.getCompilerMessage());
}
}
}
下一篇介绍了如果处置动态代码的死循环的思路：
java动态编译 （java在线执行代码后端实现原理）（二）
下面一些文章对我的理解有很大的帮助：
http://blog.onlycatch.com/post/java-Compiler-API （这篇文章循环渐进，对理解概念有很大帮助）
https://www.liaoxuefeng.com/article/0014617596492474eea2227bf04477e83e6d094683e0536000
https://www.ibm.com/developerworks/cn/java/j-jcomp/
http://www.cnblogs.com/liaoyu/p/real-time-compile-and-run-java-code-web-app.html
http://www.timehaswingss.top/blog/java/dynamic.html