StackTraceElement.java

/*
 * Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package java.lang;

import jdk.internal.loader.BuiltinClassLoader;
import jdk.internal.misc.VM;
import jdk.internal.module.ModuleHashes;
import jdk.internal.module.ModuleReferenceImpl;

import java.lang.module.ModuleReference;
import java.lang.module.ResolvedModule;
import java.util.HashSet;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;

/**
 * An element in a stack trace, as returned by {@link
 * Throwable#getStackTrace()}.  Each element represents a single stack frame.
 * All stack frames except for the one at the top of the stack represent
 * a method invocation.  The frame at the top of the stack represents the
 * execution point at which the stack trace was generated.  Typically,
 * this is the point at which the throwable corresponding to the stack trace
 * was created.
 *
 * @author Josh Bloch
 * @since 1.4
 */
// 方法调用链的栈帧
public final class StackTraceElement implements java.io.Serializable {
    private static final long serialVersionUID = 6992337162326171013L;
    
    private static final byte BUILTIN_CLASS_LOADER = 0x1;
    private static final byte JDK_NON_UPGRADEABLE_MODULE = 0x2;
    
    /**
     * For Throwables and StackWalker, the VM initially sets this field to a reference to the declaring Class.
     * The Class reference is used to construct the 'format' bitmap, and then is cleared.
     * For STEs constructed using the public constructors, this field is not used.
     */
    private transient Class<?> declaringClassObject;
    
    private byte format = 0; // Default to show all
    
    
    /*▼ 栈帧属性 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */
    
    private String moduleName;      // 模块名
    private String declaringClass;  // 类名
    private String methodName;      // 方法名
    private String fileName;        // 文件名
    private int lineNumber;         // 行号
    
    private String moduleVersion;   // 模块版本
    // Normally initialized by VM
    private String classLoaderName; // 类加载器
    
    /*▲ 栈帧属性 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */
    
    
    
    /*▼ 构造方法 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Private constructor for the factory methods to create StackTraceElement
     * for Throwable and StackFrameInfo
     */
    private StackTraceElement() {
    }
    
    /**
     * Creates a stack trace element representing the specified execution
     * point. The {@link #getModuleName module name} and {@link
     * #getModuleVersion module version} of the stack trace element will
     * be {@code null}.
     *
     * @param declaringClass the fully qualified name of the class containing
     *                       the execution point represented by the stack trace element
     * @param methodName     the name of the method containing the execution point
     *                       represented by the stack trace element
     * @param fileName       the name of the file containing the execution point
     *                       represented by the stack trace element, or {@code null} if
     *                       this information is unavailable
     * @param lineNumber     the line number of the source line containing the
     *                       execution point represented by this stack trace element, or
     *                       a negative number if this information is unavailable. A value
     *                       of -2 indicates that the method containing the execution point
     *                       is a native method
     *
     * @throws NullPointerException if {@code declaringClass} or
     *                              {@code methodName} is null
     * @revised 9
     * @spec JPMS
     * @since 1.5
     */
    public StackTraceElement(String declaringClass, String methodName, String fileName, int lineNumber) {
        this(null, null, null, declaringClass, methodName, fileName, lineNumber);
    }
    
    /**
     * Creates a stack trace element representing the specified execution
     * point.
     *
     * @param classLoaderName the class loader name if the class loader of
     *                        the class containing the execution point represented by
     *                        the stack trace is named; otherwise {@code null}
     * @param moduleName      the module name if the class containing the
     *                        execution point represented by the stack trace is in a named
     *                        module; otherwise {@code null}
     * @param moduleVersion   the module version if the class containing the
     *                        execution point represented by the stack trace is in a named
     *                        module that has a version; otherwise {@code null}
     * @param declaringClass  the fully qualified name of the class containing
     *                        the execution point represented by the stack trace element
     * @param methodName      the name of the method containing the execution point
     *                        represented by the stack trace element
     * @param fileName        the name of the file containing the execution point
     *                        represented by the stack trace element, or {@code null} if
     *                        this information is unavailable
     * @param lineNumber      the line number of the source line containing the
     *                        execution point represented by this stack trace element, or
     *                        a negative number if this information is unavailable. A value
     *                        of -2 indicates that the method containing the execution point
     *                        is a native method
     *
     * @throws NullPointerException if {@code declaringClass} is {@code null}
     *                              or {@code methodName} is {@code null}
     * @spec JPMS
     * @since 9
     */
    public StackTraceElement(String classLoaderName, String moduleName, String moduleVersion, String declaringClass, String methodName, String fileName, int lineNumber) {
        this.classLoaderName = classLoaderName;
        this.moduleName = moduleName;
        this.moduleVersion = moduleVersion;
        this.declaringClass = Objects.requireNonNull(declaringClass, "Declaring class is null");
        this.methodName = Objects.requireNonNull(methodName, "Method name is null");
        this.fileName = fileName;
        this.lineNumber = lineNumber;
    }
    
    /*▲ 构造方法 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 栈帧属性 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns the module name of the module containing the execution point
     * represented by this stack trace element.
     *
     * @return the module name of the {@code Module} containing the execution
     * point represented by this stack trace element; {@code null}
     * if the module name is not available.
     *
     * @spec JPMS
     * @see Module#getName()
     * @since 9
     */
    // 模块名
    public String getModuleName() {
        return moduleName;
    }
    
    /**
     * Returns the fully qualified name of the class containing the
     * execution point represented by this stack trace element.
     *
     * @return the fully qualified name of the {@code Class} containing
     * the execution point represented by this stack trace element.
     */
    // 类名
    public String getClassName() {
        return declaringClass;
    }
    
    /**
     * Returns the name of the method containing the execution point
     * represented by this stack trace element.  If the execution point is
     * contained in an instance or class initializer, this method will return
     * the appropriate <i>special method name</i>, {@code <init>} or
     * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual
     * Machine Specification</i>.
     *
     * @return the name of the method containing the execution point
     * represented by this stack trace element.
     */
    // 方法名
    public String getMethodName() {
        return methodName;
    }
    
    /**
     * Returns the name of the source file containing the execution point
     * represented by this stack trace element.  Generally, this corresponds
     * to the {@code SourceFile} attribute of the relevant {@code class}
     * file (as per <i>The Java Virtual Machine Specification</i>, Section
     * 4.7.7).  In some systems, the name may refer to some source code unit
     * other than a file, such as an entry in source repository.
     *
     * @return the name of the file containing the execution point
     * represented by this stack trace element, or {@code null} if
     * this information is unavailable.
     */
    // 文件名
    public String getFileName() {
        return fileName;
    }
    
    /**
     * Returns the line number of the source line containing the execution
     * point represented by this stack trace element.  Generally, this is
     * derived from the {@code LineNumberTable} attribute of the relevant
     * {@code class} file (as per <i>The Java Virtual Machine
     * Specification</i>, Section 4.7.8).
     *
     * @return the line number of the source line containing the execution
     * point represented by this stack trace element, or a negative
     * number if this information is unavailable.
     */
    // 行号
    public int getLineNumber() {
        return lineNumber;
    }
    
    /**
     * Returns the module version of the module containing the execution point
     * represented by this stack trace element.
     *
     * @return the module version of the {@code Module} containing the execution
     * point represented by this stack trace element; {@code null}
     * if the module version is not available.
     *
     * @spec JPMS
     * @see java.lang.module.ModuleDescriptor.Version
     * @since 9
     */
    // 模块版本
    public String getModuleVersion() {
        return moduleVersion;
    }
    
    /**
     * Returns the name of the class loader of the class containing the
     * execution point represented by this stack trace element.
     *
     * @return the name of the class loader of the class containing the execution
     * point represented by this stack trace element; {@code null}
     * if the class loader is not named.
     *
     * @spec JPMS
     * @see java.lang.ClassLoader#getName()
     * @since 9
     */
    // 类加载器
    public String getClassLoaderName() {
        return classLoaderName;
    }
    
    /*▲ 栈帧属性 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /**
     * Returns true if the method containing the execution point
     * represented by this stack trace element is a native method.
     *
     * @return {@code true} if the method containing the execution point
     * represented by this stack trace element is a native method.
     */
    // 是否为native方法（native方法的行号标记为-2）
    public boolean isNativeMethod() {
        return lineNumber == -2;
    }
    
    /**
     * Returns an array of StackTraceElements of the given depth filled from the backtrace of a given Throwable.
     */
    static StackTraceElement[] of(Throwable x, int depth) {
        StackTraceElement[] stackTrace = new StackTraceElement[depth];
        
        for(int i = 0; i<depth; i++) {
            stackTrace[i] = new StackTraceElement();
        }
        
        // VM to fill in StackTraceElement
        initStackTraceElements(stackTrace, x);
        
        // ensure the proper StackTraceElement initialization
        for(StackTraceElement ste : stackTrace) {
            ste.computeFormat();
        }
        
        return stackTrace;
    }
    
    /**
     * Returns a StackTraceElement from a given StackFrameInfo.
     */
    static StackTraceElement of(StackFrameInfo sfi) {
        StackTraceElement ste = new StackTraceElement();
        
        initStackTraceElement(ste, sfi);
        
        ste.computeFormat();
        
        return ste;
    }
    
    /**
     * Returns true if the module is hashed with java.base.
     * <p>
     * This method returns false when running on the exploded image
     * since JDK modules are not hashed. They have no Version attribute
     * and so "@<version>" part will be omitted anyway.
     */
    private static boolean isHashedInJavaBase(Module m) {
        // return true if module system is not initialized as the code
        // must be in java.base
        if(!VM.isModuleSystemInited())
            return true;
        
        return ModuleLayer.boot() == m.getLayer() && HashedModules.contains(m);
    }
    
    /**
     * Sets the given stack trace elements with the backtrace of the given Throwable.
     */
    private static native void initStackTraceElements(StackTraceElement[] elements, Throwable x);
    
    /**
     * Sets the given stack trace element with the given StackFrameInfo
     */
    private static native void initStackTraceElement(StackTraceElement element, StackFrameInfo sfi);
    
    
    /**
     * Returns a string representation of this stack trace element.
     *
     * @apiNote The format of this string depends on the implementation, but the
     * following examples may be regarded as typical:
     * <ul>
     * <li>
     * "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java:101)}"
     * - See the description below.
     * </li>
     * <li>
     * "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java)}"
     * - The line number is unavailable.
     * </li>
     * <li>
     * "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Unknown Source)}"
     * - Neither the file name nor the line number is available.
     * </li>
     * <li>
     * "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Native Method)}"
     * - The method containing the execution point is a native method.
     * </li>
     * <li>
     * "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}"
     * - The class of the execution point is defined in the unnamed module of
     * the class loader named {@code com.foo.loader}.
     * </li>
     * <li>
     * "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}"
     * - The class of the execution point is defined in {@code acme} module
     * loaded by a built-in class loader such as the application class loader.
     * </li>
     * <li>
     * "{@code MyClass.mash(MyClass.java:9)}"
     * - {@code MyClass} class is on the application class path.
     * </li>
     * </ul>
     *
     * <p> The first example shows a stack trace element consisting of
     * three elements, each separated by {@code "/"} followed with
     * the source file name and the line number of the source line
     * containing the execution point.
     *
     * The first element "{@code com.foo.loader}" is
     * the name of the class loader.  The second element "{@code foo@9.0}"
     * is the module name and version.  The third element is the method
     * containing the execution point; "{@code com.foo.Main"}" is the
     * fully-qualified class name and "{@code run}" is the name of the method.
     * "{@code Main.java}" is the source file name and "{@code 101}" is
     * the line number.
     *
     * <p> If a class is defined in an <em>unnamed module</em>
     * then the second element is omitted as shown in
     * "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}".
     *
     * <p> If the class loader is a <a href="ClassLoader.html#builtinLoaders">
     * built-in class loader</a> or is not named then the first element
     * and its following {@code "/"} are omitted as shown in
     * "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}".
     * If the first element is omitted and the module is an unnamed module,
     * the second element and its following {@code "/"} are also omitted
     * as shown in "{@code MyClass.mash(MyClass.java:9)}".
     *
     * <p> The {@code toString} method may return two different values on two
     * {@code StackTraceElement} instances that are
     * {@linkplain #equals(Object) equal}, for example one created via the
     * constructor, and one obtained from {@link java.lang.Throwable} or
     * {@link java.lang.StackWalker.StackFrame}, where an implementation may
     * choose to omit some element in the returned string.
     * @revised 9
     * @spec JPMS
     * @see Throwable#printStackTrace()
     */
    public String toString() {
        String s = "";
        
        if(!dropClassLoaderName() && classLoaderName != null && !classLoaderName.isEmpty()) {
            s += classLoaderName + "/";
        }
        
        if(moduleName != null && !moduleName.isEmpty()) {
            s += moduleName;
            
            if(!dropModuleVersion() && moduleVersion != null && !moduleVersion.isEmpty()) {
                s += "@" + moduleVersion;
            }
        }
        
        s = s.isEmpty() ? declaringClass : s + "/" + declaringClass;
        
        return s
            + "."
            + methodName
            + "("
            + (
            isNativeMethod()
                ? "Native Method)"
                : (
                fileName != null && lineNumber >= 0
                    ? fileName + ":" + lineNumber + ")"
                    : (
                    fileName != null
                        ? "" + fileName + ")"
                        : "Unknown Source)"
                )
            )
        );
    }
    
    /**
     * Returns true if the specified object is another
     * {@code StackTraceElement} instance representing the same execution
     * point as this instance.  Two stack trace elements {@code a} and
     * {@code b} are equal if and only if:
     * <pre>{@code
     *     equals(a.getClassLoaderName(), b.getClassLoaderName()) &&
     *     equals(a.getModuleName(), b.getModuleName()) &&
     *     equals(a.getModuleVersion(), b.getModuleVersion()) &&
     *     equals(a.getClassName(), b.getClassName()) &&
     *     equals(a.getMethodName(), b.getMethodName())
     *     equals(a.getFileName(), b.getFileName()) &&
     *     a.getLineNumber() == b.getLineNumber()
     *
     * }</pre>
     * where {@code equals} has the semantics of {@link
     * java.util.Objects#equals(Object, Object) Objects.equals}.
     *
     * @param obj the object to be compared with this stack trace element.
     *
     * @return true if the specified object is another
     * {@code StackTraceElement} instance representing the same
     * execution point as this instance.
     *
     * @revised 9
     * @spec JPMS
     */
    public boolean equals(Object obj) {
        if(obj == this)
            return true;
        
        if(!(obj instanceof StackTraceElement))
            return false;
        
        StackTraceElement e = (StackTraceElement) obj;
        
        return Objects.equals(classLoaderName, e.classLoaderName)
            && Objects.equals(moduleName, e.moduleName)
            && Objects.equals(moduleVersion, e.moduleVersion)
            && e.declaringClass.equals(declaringClass)
            && e.lineNumber == lineNumber
            && Objects.equals(methodName, e.methodName)
            && Objects.equals(fileName, e.fileName);
    }
    
    /**
     * Returns a hash code value for this stack trace element.
     */
    public int hashCode() {
        int result = 31 * declaringClass.hashCode() + methodName.hashCode();
        result = 31 * result + Objects.hashCode(classLoaderName);
        result = 31 * result + Objects.hashCode(moduleName);
        result = 31 * result + Objects.hashCode(moduleVersion);
        result = 31 * result + Objects.hashCode(fileName);
        result = 31 * result + lineNumber;
        return result;
    }
    
    
    /**
     * Called from of() methods to set the 'format' bitmap using the Class
     * reference stored in declaringClassObject, and then clear the reference.
     *
     * <p>
     * If the module is a non-upgradeable JDK module, then set
     * JDK_NON_UPGRADEABLE_MODULE to omit its version string.
     * <p>
     * If the loader is one of the built-in loaders (`boot`, `platform`, or `app`)
     * then set BUILTIN_CLASS_LOADER to omit the first element (`<loader>/`).
     */
    private synchronized void computeFormat() {
        try {
            Class<?> cls = (Class<?>) declaringClassObject;
            ClassLoader loader = cls.getClassLoader0();
            Module m = cls.getModule();
            byte bits = 0;
            
            // First element - class loader name
            // Call package-private ClassLoader::name method
            
            if(loader instanceof BuiltinClassLoader) {
                bits |= BUILTIN_CLASS_LOADER;
            }
            
            // Second element - module name and version
            
            // Omit if is a JDK non-upgradeable module (recorded in the hashes in java.base)
            if(isHashedInJavaBase(m)) {
                bits |= JDK_NON_UPGRADEABLE_MODULE;
            }
            
            format = bits;
        } finally {
            // Class reference no longer needed, clear it
            declaringClassObject = null;
        }
    }
    
    private boolean dropClassLoaderName() {
        return (format & BUILTIN_CLASS_LOADER) == BUILTIN_CLASS_LOADER;
    }
    
    private boolean dropModuleVersion() {
        return (format & JDK_NON_UPGRADEABLE_MODULE) == JDK_NON_UPGRADEABLE_MODULE;
    }
    
    /**
     * Finds JDK non-upgradeable modules, i.e. the modules that are
     * included in the hashes in java.base.
     */
    private static class HashedModules {
        static Set<String> HASHED_MODULES = hashedModules();
        
        static Set<String> hashedModules() {
            Optional<ResolvedModule> resolvedModule = ModuleLayer.boot().configuration().findModule("java.base");
            
            assert resolvedModule.isPresent();
            
            ModuleReference mref = resolvedModule.get().reference();
            
            assert mref instanceof ModuleReferenceImpl;
            
            ModuleHashes hashes = ((ModuleReferenceImpl) mref).recordedHashes();
            if(hashes != null) {
                Set<String> names = new HashSet<>(hashes.names());
                names.add("java.base");
                return names;
            }
            
            return Set.of();
        }
        
        static boolean contains(Module m) {
            return HASHED_MODULES.contains(m.getName());
        }
    }
}