用Java实现JVM第六章《类和对象》

2019/05/07

案例介绍

本案例通过java代码实现jvm规范中指令集和解释器,完成后就可以开始执行1到100的加和计算。

Java虚拟机顾名思义,就是一台虚拟的机器,而字节码(bytecode)就是运行在这台虚拟机器上的机器码。我们已经知道,每一个类或者接口都会被Java编译器编译成一个class文件,类或接口的方法信息就放在class文件的method_info结构中。如果方法不是抽象的,也不是本地方法,方法的Java代码就会被编译器编译成字节码(即使方法是空的,编译器也会生成一条return语句),存在method_info结构的Code属性中。

环境准备

  1. jdk 1.8.0
  2. IntelliJ IDEA Community Edition 2018.3.1 x64

配置信息

  1. 调试配置
    1. 配置位置:Run/Debug Configurations -> program arguments
    2. 配置内容:-Xjre “C:\Program Files\Java\jdk1.8.0_161\jre” E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-06\target\test-classes\org\itstack\demo\test\HelloWorld

代码示例

itstack-demo-jvm-06
├── pom.xml
└── src
    └── main
        └── java
            └── org.itstack.demo.jvm
	             ├── classfile
                    ├── attributes   {BootstrapMethods/Code/ConstantValue...}
                    ├── constantpool {CONSTANT_TAG_CLASS/CONSTANT_TAG_FIELDREF/CONSTANT_TAG_METHODREF...}
                    ├── ClassFile.java
                    ├── ClassReader.java
                    └── MemberInfo.java	
                 ├── classpath
                    ├── impl
                       ├── CompositeEntry.java
                       ├── DirEntry.java 
                       ├── WildcardEntry.java 
                       └── ZipEntry.java    
                    ├── Classpath.java
                    └── Entry.java   
                 ├── classpath
                    ├── base
                    ├── comparisons
                    ├── constants
                    ├── control
                    ├── conversions
                    ├── extended
                    ├── loads
                    ├── math
                       ├── add
                       ├── and
                       ├── div
                       ├── iinc
                       ├── mul
                       ├── neg
                       ├── or
                       ├── rem
                       ├── sh
                       ├── sub
                       └── xor
                    ├── stack
                    ├── store
                    └── Factory	
                 ├── rtda
                    ├── heap
                       ├── constantpool
                       ├── methodarea
                          ├── Class.java 	
                          ├── ClassMember.java	
                          ├── Field.java	
                          ├── Method.java	
                          ├── Object.java	
                          └── Slots.java		
                       └── ClassLoader.java	
                    ├── Frame.java
                    ├── JvmStack.java
                    ├── LocalVars.java
                    ├── OperandStack.java
                    ├── Slot.java	
                    └── Thread.java
                 ├── Cmd.java
                 ├── Interpret.java	
                 └── Main.java
    └── test
         └── java
             └── org.itstack.demo.test
                 └── HelloWorld.java

Class.java

public class Class {

    public int accessFlags;
    public String name;
    public String superClassName;
    public String[] interfaceNames;
    public RunTimeConstantPool runTimeConstantPool;
    public Field[] fields;
    public Method[] methods;
    public ClassLoader loader;
    public Class superClass;
    public Class[] interfaces;
    public int instanceSlotCount;
    public int staticSlotCount;
    public Slots staticVars;

    public Class(ClassFile classFile) {
        this.accessFlags = classFile.accessFlags();
        this.name = classFile.className();
        this.superClassName = classFile.superClassName();
        this.interfaceNames = classFile.interfaceNames();
        this.runTimeConstantPool = new RunTimeConstantPool(this, classFile.constantPool());
        this.fields = new Field().newFields(this, classFile.fields());
        this.methods = new Method().newMethods(this, classFile.methods());
    }

    public boolean isPublic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PUBLIC);
    }

    public boolean isFinal() {
        return 0 != (this.accessFlags & AccessFlags.ACC_FINAL);
    }

    public boolean isSuper() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SUPER);
    }

    public boolean isInterface() {
        return 0 != (this.accessFlags & AccessFlags.ACC_INTERFACE);
    }

    public boolean isAbstract() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ABSTRACT);
    }

    public boolean isSynthetic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNTHETIC);
    }

    public boolean isAnnotation() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ANNOTATION);
    }

    public boolean isEnum() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ENUM);
    }

    public RunTimeConstantPool constantPool() {
        return this.runTimeConstantPool;
    }

    public Slots staticVars() {
        return this.staticVars;
    }

    public boolean isAccessibleTo(Class other) {
        return this.isPublic() || this.getPackageName().equals(other.getPackageName());
    }

    public String getPackageName() {
        int i = this.name.lastIndexOf("/");
        if (i >= 0) return this.name;
        return "";
    }

    public Method getMainMethod() {
        return this.getStaticMethod("main", "([Ljava/lang/String;)V");
    }

    private Method getStaticMethod(String name, String descriptor) {
        for (Method method : this.methods) {
            if (method.name.equals(name) && method.descriptor.equals(descriptor)) {
                return method;
            }
        }
        return null;
    }

    public Object newObject() {
        return new Object(this);
    }

    public boolean isAssignableFrom(Class other) {
        if (this == other) return true;
        if (!other.isInterface()) {
            return this.isSubClassOf(other);
        } else {
            return this.isImplements(other);
        }
    }

    public boolean isSubClassOf(Class other) {
        for (Class c = this.superClass; c != null; c = c.superClass) {
            if (c == other) {
                return true;
            }
        }
        return false;
    }

    private boolean isImplements(Class other) {

        for (Class c = this; c != null; c = c.superClass) {
            for (Class clazz : c.interfaces) {
                if (clazz == other || clazz.isSubInterfaceOf(other)) {
                    return true;
                }
            }
        }
        return false;

    }

    public boolean isSubInterfaceOf(Class iface) {
        for (Class superInterface : this.interfaces) {
            if (superInterface == iface || superInterface.isSubInterfaceOf(iface)) {
                return true;
            }
        }
        return false;
    }

}

ClassMember.java

public class ClassMember {

    public int accessFlags;
    public String name;
    public String descriptor;
    public Class clazz;

    public void copyMemberInfo(MemberInfo memberInfo) {
        this.accessFlags = memberInfo.accessFlags();
        this.name = memberInfo.name();
        this.descriptor = memberInfo.descriptor();
    }

    public boolean isPublic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PUBLIC);
    }

    public boolean isPrivate() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PRIVATE);
    }

    public boolean isProtected() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PROTECTED);
    }

    public boolean isStatic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_STATIC);
    }

    public boolean isFinal() {
        return 0 != (this.accessFlags & AccessFlags.ACC_FINAL);
    }

    public boolean isSynthetic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNTHETIC);
    }

    public String name() {
        return this.name;
    }

    public String descriptor() {
        return this.descriptor;
    }

    public Class clazz() {
        return this.clazz;
    }

    public boolean isAccessibleTo(Class d) {
        if (this.isPublic()) {
            return true;
        }
        Class c = this.clazz;
        if (this.isProtected()) {
            return d == c || c.getPackageName().equals(d.getPackageName());
        }
        if (!this.isPrivate()) {
            return c.getPackageName().equals(d.getPackageName());
        }
        return d == c;
    }

}

Field.java

package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.classfile.MemberInfo;
import org.itstack.demo.jvm.classfile.attributes.impl.ConstantValueAttribute;
import org.itstack.demo.jvm.rtda.heap.constantpool.AccessFlags;

public class Field extends ClassMember {

    public int constValueIndex;
    public int slotId;

    public Field[] newFields(Class clazz, MemberInfo[] cfFields) {
        Field[] fields = new Field[cfFields.length];
        for (int i = 0; i < cfFields.length; i++) {
            fields[i] = new Field();
            fields[i].clazz = clazz;
            fields[i].copyMemberInfo(cfFields[i]);
            fields[i].copyAttributes(cfFields[i]);
        }
        return fields;
    }

    public void copyAttributes(MemberInfo cfField) {
        ConstantValueAttribute valAttr = cfField.ConstantValueAttribute();
        if (null != valAttr) {
            this.constValueIndex = valAttr.constantValueIdx();
        }
    }

    public boolean isVolatile() {
        return 0 != (this.accessFlags & AccessFlags.ACC_VOLATILE);
    }

    public boolean isTransient() {
        return 0 != (this.accessFlags & AccessFlags.ACC_TRANSIENT);
    }

    public boolean isEnum() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ENUM);
    }

    public int constValueIndex() {
        return this.constValueIndex;
    }

    public int slotId() {
        return this.slotId;
    }

    public boolean isLongOrDouble() {
        return this.descriptor.equals("J") || this.descriptor.equals("D");
    }


}

Method.java

package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.classfile.MemberInfo;
import org.itstack.demo.jvm.classfile.attributes.impl.CodeAttribute;
import org.itstack.demo.jvm.rtda.heap.constantpool.AccessFlags;

public class Method extends ClassMember {

    public int maxStack;
    public int maxLocals;
    public byte[] code;

    public Method[] newMethods(Class clazz, MemberInfo[] cfMethods) {
        Method[] methods = new Method[cfMethods.length];
        for (int i = 0; i < cfMethods.length; i++) {
            methods[i] = new Method();
            methods[i].clazz = clazz;
            methods[i].copyMemberInfo(cfMethods[i]);
            methods[i].copyAttributes(cfMethods[i]);
        }
        return methods;
    }

    public void copyAttributes(MemberInfo cfMethod) {
        CodeAttribute codeAttr = cfMethod.codeAttribute();
        if (null != codeAttr) {
            this.maxStack = codeAttr.maxStack();
            this.maxLocals = codeAttr.maxLocals();
            this.code = codeAttr.data();
        }
    }

    public boolean isSynchronized() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNCHRONIZED);
    }

    public boolean isBridge() {
        return 0 != (this.accessFlags & AccessFlags.ACC_BRIDGE);
    }

    public boolean isVarargs() {
        return 0 != (this.accessFlags & AccessFlags.ACC_VARARGS);
    }

    public boolean isNative() {
        return 0 != (this.accessFlags & AccessFlags.ACC_NATIVE);
    }

    public boolean isAbstract() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ABSTRACT);
    }

    public boolean isStrict() {
        return 0 != (this.accessFlags & AccessFlags.ACC_STRICT);
    }

    public int maxStack() {
        return this.maxStack;
    }

    public int maxLocals() {
        return this.maxLocals;
    }

    public byte[] code() {
        return this.code;
    }

}

Object.java

package org.itstack.demo.jvm.rtda.heap.methodarea;

public class Object {

    Class clazz;
    Slots fields;

    public Object(Class clazz){
        this.clazz = clazz;
        this.fields = new Slots(clazz.instanceSlotCount);
    }

    public Class clazz(){
        return this.clazz;
    }

    public Slots fields(){
        return this.fields;
    }

    public boolean isInstanceOf(Class clazz){
        return clazz.isAssignableFrom(this.clazz);
    }

}

Slots.java

package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.rtda.Slot;

public class Slots {

    private Slot[] slots;

    public Slots(int slotCount) {
        if (slotCount > 0) {
            slots = new Slot[slotCount];
            for (int i = 0; i < slotCount; i++) {
                slots[i] = new Slot();
            }
        }
    }

    public void setInt(int idx, int val) {
        this.slots[idx].num = val;
    }

    public int getInt(int idx) {
        return this.slots[idx].num;
    }

    public void setFloat(int idx, float val) {
        this.slots[idx].num = (int) val;
    }

    public float getFloat(int idx) {
        return this.slots[idx].num;
    }

    public void setLong(int idx, long val) {
        this.slots[idx].num = (int) val;
        this.slots[idx + 1].num = (int) (val >> 32);
    }

    public long getLong(int idx) {
        int low = this.slots[idx].num;
        int high = this.slots[idx + 1].num;
        return (long) high << 32 | (long) low;
    }

    public void setDouble(int idx, double val) {
        this.setLong(idx, (long) val);
    }

    public Double getDouble(int idx) {
        return (double) this.getLong(idx);
    }

    public void setRef(int idx, Object ref) {
        this.slots[idx].ref = ref;
    }

    public Object getRef(int idx){
        return this.slots[idx].ref;
    }

}

测试结果 {可以看到已经输出;5050}

"C:\Program Files\Java\jdk1.8.0_161\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\lib\idea_rt.jar=61887:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_161\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\rt.jar;E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-05\target\classes;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\beust\jcommander\1.72\jcommander-1.72.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\org\projectlombok\lombok\1.18.0\lombok-1.18.0.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\alibaba\fastjson\1.2.40\fastjson-1.2.40.jar" org.itstack.demo.jvm.Main -Xjre "C:\Program Files\Java\jdk1.8.0_161\jre" E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-05\target\test-classes\org\itstack\demo\test\HelloWorld
classpath:org.itstack.demo.jvm.classpath.Classpath@4bf558aa class:E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-05\target\test-classes\org\itstack\demo\test\HelloWorld args:null
寄存器(指令)0x03 -> ICONST_0 => 局部变量表:[{"num":0},{"num":0}] 操作数栈:[{"num":0},{"num":0}]
寄存器(指令)0x3c -> ISTORE_1 => 局部变量表:[{"num":0},{"num":0}] 操作数栈:[{"num":0},{"num":0}]
寄存器(指令)0x04 -> ICONST_1 => 局部变量表:[{"num":0},{"num":0}] 操作数栈:[{"num":0},{"num":0}]
寄存器(指令)0x3d -> ISTORE_2 => 局部变量表:[{"num":1},{"num":0}] 操作数栈:[{"num":1},{"num":0}]
寄存器(指令)0x1c -> ILOAD_2 => 局部变量表:[{"num":1},{"num":0}] 操作数栈:[{"num":1},{"num":0}]
寄存器(指令)0x10 -> BIPUSH => 局部变量表:[{"num":1},{"num":0}] 操作数栈:[{"num":1},{"num":0}]
寄存器(指令)0xa3 -> IF_ICMPGT => 局部变量表:[{"num":1},{"num":100}] 操作数栈:[{"num":1},{"num":100}]
寄存器(指令)0x1b -> ILOAD_1 => 局部变量表:[{"num":1},{"num":100}] 操作数栈:[{"num":1},{"num":100}]
寄存器(指令)0x1c -> ILOAD_2 => 局部变量表:[{"num":0},{"num":100}] 操作数栈:[{"num":0},{"num":100}]

... ...

寄存器(指令)0x60 -> IADD => 局部变量表:[{"num":4950},{"num":100}] 操作数栈:[{"num":4950},{"num":100}]
寄存器(指令)0x3c -> ISTORE_1 => 局部变量表:[{"num":5050},{"num":100}] 操作数栈:[{"num":5050},{"num":100}]
寄存器(指令)0x84 -> IINC => 局部变量表:[{"num":5050},{"num":100}] 操作数栈:[{"num":5050},{"num":100}]
寄存器(指令)0xa7 -> GOTO => 局部变量表:[{"num":5050},{"num":100}] 操作数栈:[{"num":5050},{"num":100}]
寄存器(指令)0x1c -> ILOAD_2 => 局部变量表:[{"num":5050},{"num":100}] 操作数栈:[{"num":5050},{"num":100}]
寄存器(指令)0x10 -> BIPUSH => 局部变量表:[{"num":101},{"num":100}] 操作数栈:[{"num":101},{"num":100}]
寄存器(指令)0xa3 -> IF_ICMPGT => 局部变量表:[{"num":101},{"num":100}] 操作数栈:[{"num":101},{"num":100}]
5050
寄存器(指令)0xb1 -> RETURN => 局部变量表:[{"num":101},{"num":5050}] 操作数栈:[{"num":101},{"num":5050}]
Exception in thread "main" java.lang.RuntimeException: jvm stack is empty!
	at org.itstack.demo.jvm.rtda.JvmStack.pop(JvmStack.java:33)


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