無法在運行時類擴展已編譯

Question

我已經將此答案作為在運行時編譯類的參考，它可以正常工作。 所以現在我需要擴展實際上找不到的已編譯類。

我已經試過了：

import java.io.File;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;

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.ToolProvider;

public class CompileSourceInMemory {

    public static Class<?> compile(String className, String sourceCode, URLClassLoader classLoader) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();

        JavaFileObject file = new JavaSourceFromString(className, sourceCode);

        Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file);
        CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);

        boolean success = task.call();

        for (Diagnostic<?> diagnostic : diagnostics.getDiagnostics()) {
            System.out.println(diagnostic.getCode());
            System.out.println(diagnostic.getKind());
            System.out.println(diagnostic.getPosition());
            System.out.println(diagnostic.getStartPosition());
            System.out.println(diagnostic.getEndPosition());
            System.out.println(diagnostic.getSource());
            System.out.println(diagnostic.getMessage(null));
        }

        System.out.println("Success: " + success);

        if (success) {
            return Class.forName(className.replace(".", "/"), true, classLoader);
        } else {
            throw new Exception("Didn't work!");
        }
    }

    public static void main(String args[]) throws Exception {
        URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new File("").toURI().toURL() });
        StringBuilder sourceCode = new StringBuilder();
        // sourceCode.append("package br.bla;");
        sourceCode.append("public class HelloWorld {");
        sourceCode.append("  public static void main(String args[]) {");
        sourceCode.append("    System.out.append(\"This is in another java file\");");
        sourceCode.append("  }");
        sourceCode.append("}");
        Class<?> helloWorld = compile("HelloWorld", sourceCode.toString(), classLoader);

        sourceCode = new StringBuilder();
        // sourceCode.append("package br.bla;");
        sourceCode.append("public class ExtendedHelloWorld extends HelloWorld {");
        sourceCode.append("  public int i = 2;");
        sourceCode.append("}");

        Class<?> extendedHelloWorld = compile("ExtendedHelloWorld", sourceCode.toString(), classLoader);
        Object object = extendedHelloWorld.newInstance();

        return;
    }
}

class JavaSourceFromString extends SimpleJavaFileObject {
    final String code;

    JavaSourceFromString(String name, String code) {
        super(URI.create("string:///" + name.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
        this.code = code;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
        return code;
    }
}

輸出為：

Success: true
compiler.err.cant.resolve
ERROR
40
40
50
JavaSourceFromString[string:///ExtendedHelloWorld.java]
cannot find symbol
  symbol: class HelloWorld
Success: false

有人知道如何編譯我的ExtendedHelloWorld類嗎？

Answer 1

編譯HelloWorld之所以成功，是因為它只需要自己的源即可。 當您嘗試編譯ExtendedHelloWorld它會失敗，因為它需要自己的源代碼和HelloWorld的源代碼。 這可以通過將每個類存儲在HashMap<String, String>中來實現，其中key是類名， value是類的源代碼。

---

我建議您對代碼進行一些更改。

我將縮小您的compile方法，並將其分為兩種不同的編譯方法。 當您要編譯不擴展從內存編譯的類的類時，將使用第一個。 當您確實想編譯擴展從內存編譯的類的類時，將使用第二個類。

/*
 * Method to compile a class which doesn't extend a class that's been compiled from memory.
 */
public static Class<?> compile(String className, String sourceCode, URLClassLoader classLoader) throws Exception {
    return compileHelper(className, classLoader, Arrays.asList(new JavaSourceFromString(className, sourceCode)));
}

/*
 * Method to compile a class which extends a class that's been compiled from
 * memory.
 * 
 * This method takes in the class name, a Set of Map.Entry<String, String>,
 * which contains class names and their sources, and a class loader. This
 * method iterates over the entries in the Set, creates JavaFileObjects from
 * the class names and their sources and adds each JavaFileObject to an
 * ArrayList which will be used in the 'compileHelper' method.
 */
public static Class<?> compile(String className, Set<Map.Entry<String, String>> nameAndSource, URLClassLoader classLoader) throws Exception {
    List<JavaFileObject> compilationUnits = new ArrayList<>();

    for(Entry<String, String> entry : nameAndSource) {
        compilationUnits.add(new JavaSourceFromString(entry.getKey(), entry.getValue()));
    }

    return compileHelper(className, classLoader, compilationUnits);
}

然后，上述方法將調用一個輔助方法，該方法將實際編譯該類。 此方法與您的compile方法非常相似，但是診斷的輸出已移至單獨的方法printDiagnostics(diagnostics) 。

/*
 * Helper method that actually does the compiling.
 */
private static Class<?> compileHelper(String className, URLClassLoader classLoader, Iterable<? extends JavaFileObject> compilationUnits) throws Exception {
    JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
    DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
    CompilationTask task = null;
    boolean success = false;

    // debug compilation units section
    System.out.println("Compiling " + className);

    System.out.println(" - compilationUnits ");
    for(JavaFileObject o : compilationUnits) {
        System.out.println("   + " + o.toString());
    }
    // end debug

    task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);
    success = task.call();

    if (success) {
        System.out.println("Successful compilation of " + className);
        return Class.forName(className.replace(".", "/"), true, classLoader);
    } else {
        System.out.println("Failed while compiling " + className);
        printDiagnostics(diagnostics);
        throw new Exception("It didn't work!");
    }
}

為了使用上面的方法，您需要使用HashMap<String, String>來存儲您要編譯的每個類的類名和源代碼。 然后，當你准備編譯撥打電話，以compile在過往entrySet()從HashMap ，如： compile(className, nameAndSource.entrySet(), classLoader)

例如：

public static void main(String args[]) throws Exception {
    Map<String, String> nameAndSource = new HashMap<>();
    URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new File("").toURI().toURL() });
    String className;
    StringBuilder sourceCode;

    // HelloWorld class
    className = "HelloWorld";
    sourceCode = new StringBuilder();        
    sourceCode.append("public class HelloWorld {");
    sourceCode.append("  public static void main(String args[]) {");
    sourceCode.append("    System.out.append(\"This is in another java file\");");
    sourceCode.append("  }");
    sourceCode.append("}");

    // pass the class name and source code to 'compile'        
    Class<?> helloWorld = compile(className, sourceCode.toString(), classLoader);

    // add HelloWorld class name and source code to HashMap
    nameAndSource.put(className, sourceCode.toString());

    // ExtendedHelloWorldClass
    className = "ExtendedHelloWorld";
    sourceCode = new StringBuilder();
    sourceCode.append("public class ExtendedHelloWorld extends HelloWorld {");
    sourceCode.append("  public int num = 2;");
    sourceCode.append("}");

    // add ExtendedHelloWorld class name and source code to HashMap
    nameAndSource.put(className, sourceCode.toString());

    // here's where we pass in the nameAndSource entrySet()
    Class<?> extendedHelloWorld = compile(className, nameAndSource.entrySet(), classLoader);

    return;
}

---

這是我上面描述的完整源代碼：

public class CompileSourceInMemory {

    /*
     * Method to compile a class which extends a class that's been compiled from
     * memory.
     * 
     * This method takes in the class name, a Set of Map.Entry<String, String>,
     * which contains class names and their sources, and a class loader. This
     * method iterates over the entries in the Set, creates JavaFileObjects from
     * the class names and their sources and adds each JavaFileObject to an
     * ArrayList which will be used the private compile method.
     */
    public static Class<?> compile(String className, Set<Map.Entry<String, String>> nameAndSource, URLClassLoader classLoader) throws Exception {
        List<JavaFileObject> compilationUnits = new ArrayList<>();

        for (Entry<String, String> entry : nameAndSource) {
            compilationUnits.add(newJavaSourceFromString(entry.getKey(), entry.getValue()));
        }

        return compileHelper(className, classLoader, compilationUnits);
    }

    /*
     * Method to compile a class which doesn't extend a class that's been
     * compiled from memory.
     */
    public static Class<?> compile(String className, String sourceCode, URLClassLoader classLoader) throws Exception {
        return compileHelper(className, classLoader, Arrays.asList(new JavaSourceFromString(className, sourceCode)));
    }

    /*
     * Helper method that actually does the compiling.
     */
    private static Class<?> compileHelper(String className, URLClassLoader classLoader, Iterable<? extends JavaFileObject> compilationUnits) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
        CompilationTask task = null;
        boolean success = false;

        // debug compilation units section
        System.out.println("Compiling " + className);

        System.out.println(" - compilationUnits ");
        for (JavaFileObject o : compilationUnits) {
            System.out.println("   + " + o.toString());
        }
        // end debug

        task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits);
        success = task.call();

        if (success) {
            System.out.println("Successful compilation of " + className);
            return Class.forName(className.replace(".", "/"), true, classLoader);
        } else {
            System.out.println("Failed while compiling " + className);
            printDiagnostics(diagnostics);
            throw new Exception("It didn't work!");
        }
    }

    public static void main(String args[]) throws Exception {
        Map<String, String> nameAndSource = new HashMap<>();
        URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new File("").toURI().toURL() });
        String className;
        StringBuilder sourceCode;

        // HelloWorld Class
        className = "HelloWorld";
        sourceCode = new StringBuilder();
        sourceCode.append("public class HelloWorld {");
        sourceCode.append("  public static void main(String args[]) {");
        sourceCode.append("    System.out.append(\"This is in another java file\");");
        sourceCode.append("  }");
        sourceCode.append("}");

        // pass the class name and source code to 'compile'
        Class<?> helloWorld = compile(className, sourceCode.toString(), classLoader);

        // add HelloWorld class name and source code to HashMap
        nameAndSource.put(className, sourceCode.toString());

        // ExtendedHelloWorld Class
        className = "ExtendedHelloWorld";
        sourceCode = new StringBuilder();
        sourceCode.append("public class ExtendedHelloWorld extends HelloWorld {");
        sourceCode.append("  public int num = 2;");
        sourceCode.append("}");

        // add ExtendedHelloWorld class name and source code to HashMap
        nameAndSource.put(className, sourceCode.toString());

        // pass the nameAndSource entrySet() to 'compile'
        Class<?> extendedHelloWorld = compile(className, nameAndSource.entrySet(), classLoader);

        // ExtendedExtendedHelloWorld Class
        className = "ExtendedExtendedHelloWorld";
        sourceCode = new StringBuilder();
        sourceCode.append("public class ExtendedExtendedHelloWorld extends ExtendedHelloWorld {");
        sourceCode.append("  public void printNum() { System.out.println(num); }");
        sourceCode.append("}");

        // add ExtendedExtendedHelloWorld class name and source code to HashMap
        nameAndSource.put(className, sourceCode.toString());

        // pass the nameAndSource entrySet() to 'compile'
        Class<?> extendedExtendedHelloWorld = compile(className, nameAndSource.entrySet(), classLoader);
        Object eehw = extendedExtendedHelloWorld.newInstance();

        return;
    }

    private static void printDiagnostics(DiagnosticCollector<JavaFileObject> diagnostics) {
        StringBuilder sb = new StringBuilder("-- Diagnostics --\n");
        for (Diagnostic<?> d : diagnostics.getDiagnostics()) {
            sb.append(String
                    .format("d.getCode() - %s%nd.getKind() - %s%nd.getPosition() - %d%nd.getStartPosition() - %d%nd.getEndPosition() - %d%nd.getSource() - %s%nd.getMessage(null) - %s%n",
                            d.getCode(), d.getKind().toString(),
                            d.getPosition(), d.getStartPosition(),
                            d.getEndPosition(), d.getSource().toString(),
                            d.getMessage(null)));
        }
        System.out.println(sb.append("--").toString());
    }
}

class JavaSourceFromString extends SimpleJavaFileObject {
    final String code;

    JavaSourceFromString(String name, String code) {
        super(URI.create("string:///" + name.replace('.', '/')
                + Kind.SOURCE.extension), Kind.SOURCE);
        this.code = code;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
        return code;
    }
}

這是運行上面的代碼的輸出：

Compiling HelloWorld
 - compilationUnits 
   + JavaSourceFromString[string:///HelloWorld.java]
Successful compilation of HelloWorld
Compiling ExtendedHelloWorld
 - compilationUnits 
   + JavaSourceFromString[string:///ExtendedHelloWorld.java]
   + JavaSourceFromString[string:///HelloWorld.java]
Successful compilation of ExtendedHelloWorld
Compiling ExtendedExtendedHelloWorld
 - compilationUnits 
   + JavaSourceFromString[string:///ExtendedHelloWorld.java]
   + JavaSourceFromString[string:///ExtendedExtendedHelloWorld.java]
   + JavaSourceFromString[string:///HelloWorld.java]
Successful compilation of ExtendedExtendedHelloWorld