InputStream类中重要的函数,只有一个抽象的有用, public abstract int read() throws IOException; 其他两个read的意义不大。 public int read(byte b[], int off, int len) throws IOException 和 public int read(byte b[]) throws IOException { return read(b, 0, b.length); } 下面看它的子类FileInputStream的实现, /* File Descriptor - handle to the open file */ private FileDescriptor fd; 这个很重要,这是文件句柄,C语言使用fopen函数的都知道。 /** * Opens the specified file for reading. * @param name the name of the file */ private native void open(String name) throws FileNotFoundException; /** * Reads a byte of data from this input stream. This method blocks * if no input is yet available. * * @return the next byte of data, or <code>-1</code> if the end of the * file is reached. * @exception IOException if an I/O error occurs. */ public native int read() throws IOException; /** * Reads a subarray as a sequence of bytes. * @param b the data to be written * @param off the start offset in the data * @param len the number of bytes that are written * @exception IOException If an I/O error has occurred. */ private native int readBytes(byte b[], int off, int len) throws IOException; 子类修改了父的实现 /** * Reads up to <code>b.length</code> bytes of data from this input * stream into an array of bytes. This method blocks until some input * is available. * * @param b the buffer into which the data is read. * @return the total number of bytes read into the buffer, or * <code>-1</code> if there is no more data because the end of * the file has been reached. * @exception IOException if an I/O error occurs. */ public int read(byte b[]) throws IOException { return readBytes(b, 0, b.length); } /** * Reads up to <code>len</code> bytes of data from this input stream * into an array of bytes. If <code>len</code> is not zero, the method * blocks until some input is available; otherwise, no * bytes are read and <code>0</code> is returned. * * @param b the buffer into which the data is read. * @param off the start offset in the destination array <code>b</code> * @param len the maximum number of bytes read. * @return the total number of bytes read into the buffer, or * <code>-1</code> if there is no more data because the end of * the file has been reached. * @exception NullPointerException If <code>b</code> is <code>null</code>. * @exception IndexOutOfBoundsException If <code>off</code> is negative, * <code>len</code> is negative, or <code>len</code> is greater than * <code>b.length - off</code> * @exception IOException if an I/O error occurs. */ public int read(byte b[], int off, int len) throws IOException { return readBytes(b, off, len); } 看出readBytes是关键的所在,windows的native code中只有 JNIEXPORT void JNICALL Java_java_io_FileInputStream_close0(JNIEnv *env, jobject this) { handleClose(env, this, fis_fd); } 是平台相关的。 其他的在share中 FileInputStream.c代码 jfieldID fis_fd; /* id for jobject 'fd' in java.io.FileInputStream */ /************************************************************** * static methods to store field ID's in initializers */ 得到fd的值,这个很重要 JNIEXPORT void JNICALL Java_java_io_FileInputStream_initIDs(JNIEnv *env, jclass fdClass) { fis_fd = (*env)->GetFieldID(env, fdClass, "fd", "Ljava/io/FileDescriptor;"); } /************************************************************** * Input stream */ JNIEXPORT void JNICALL Java_java_io_FileInputStream_open(JNIEnv *env, jobject this, jstring path) { fileOpen(env, this, path, fis_fd, O_RDONLY); } JNIEXPORT jint JNICALL Java_java_io_FileInputStream_read(JNIEnv *env, jobject this) { return readSingle(env, this, fis_fd); } JNIEXPORT jint JNICALL Java_java_io_FileInputStream_readBytes(JNIEnv *env, jobject this, jbyteArray bytes, jint off, jint len) { return readBytes(env, this, bytes, off, len, fis_fd); } JNIEXPORT jlong JNICALL Java_java_io_FileInputStream_skip(JNIEnv *env, jobject this, jlong toSkip) { jlong cur = jlong_zero; jlong end = jlong_zero; FD fd = GET_FD(this, fis_fd); if ((cur = IO_Lseek(fd, (jlong)0, (jint)SEEK_CUR)) == -1) { JNU_ThrowIOExceptionWithLastError(env, "Seek error"); } else if ((end = IO_Lseek(fd, toSkip, (jint)SEEK_CUR)) == -1) { JNU_ThrowIOExceptionWithLastError(env, "Seek error"); } return (end - cur); } JNIEXPORT jint JNICALL Java_java_io_FileInputStream_available(JNIEnv *env, jobject this) { jlong ret; FD fd = GET_FD(this, fis_fd); if (IO_Available(fd, &ret)) { if (ret > INT_MAX) { ret = (jlong) INT_MAX; } return jlong_to_jint(ret); } JNU_ThrowIOExceptionWithLastError(env, NULL); return 0; } 主要是readBytes的实现,打开io_util.c文件 /* IO helper functions */ int readSingle(JNIEnv *env, jobject this, jfieldID fid) { int nread; char ret; FD fd = GET_FD(this, fid); nread = IO_Read(fd, &ret, 1); if (nread == 0) { /* EOF */ return -1; } else if (nread == JVM_IO_ERR) { /* error */ JNU_ThrowIOExceptionWithLastError(env, "Read error"); } else if (nread == JVM_IO_INTR) { JNU_ThrowByName(env, "java/io/InterruptedIOException", 0); } return ret & 0xFF; } /* The maximum size of a stack-allocated buffer. */ #define BUF_SIZE 8192 int readBytes(JNIEnv *env, jobject this, jbyteArray bytes, jint off, jint len, jfieldID fid) { int nread, datalen; char stackBuf[BUF_SIZE]; char *buf = 0; FD fd; if (IS_NULL(bytes)) { JNU_ThrowNullPointerException(env, 0); return -1; } datalen = (*env)->GetArrayLength(env, bytes); if ((off < 0) || (off > datalen) || (len < 0) || ((off + len) > datalen) || ((off + len) < 0)) { JNU_ThrowByName(env, "java/lang/IndexOutOfBoundsException", 0); return -1; } if (len == 0) { return 0; } else if (len > BUF_SIZE) { buf = malloc(len); if (buf == 0) { JNU_ThrowOutOfMemoryError(env, 0); return 0; } } else { buf = stackBuf; } fd = GET_FD(this, fid); nread = IO_Read(fd, buf, len); if (nread > 0) { (*env)->SetByteArrayRegion(env, bytes, off, nread, (jbyte *)buf); } else if (nread == JVM_IO_ERR) { JNU_ThrowIOExceptionWithLastError(env, "Read error"); } else if (nread == JVM_IO_INTR) { /* EOF */ JNU_ThrowByName(env, "java/io/InterruptedIOException", 0); } else { /* EOF */ nread = -1; } if (buf != stackBuf) { free(buf); } return nread; } 注意IO_Read在io_util_md.h做了手脚的, #define IO_Read JVM_Read 其实就是JVM_Read,JVM_Read在hotspot源码中定义的 //%note jvm_r6 return (jint)hpi::read(fd, buf, nbytes); hpi定义了大量的函数 // HPI_FileInterface static inline char* native_path(char *path); static inline int file_type(const char *path); static inline int open(const char *name, int mode, int perm); static inline int close(int fd); static inline jlong lseek(int fd, jlong off, int whence); static inline int ftruncate(int fd, jlong length); static inline int fsync(int fd); static inline int available(int fd, jlong *bytes); static inline size_t read(int fd, void *buf, unsigned int nBytes); static inline size_t write(int fd, const void *buf, unsigned int nBytes); static inline int fsize(int fd, jlong *size); 这就是和平台相关的代码了。window下通过HPIDECL宏转换的 这就是源代码的一小段,根据他的描述,里面都有c的fopen等函数,都是有内存操作的,所以一开始就进入内存了
public abstract int read() throws IOException;
其他两个read的意义不大。
public int read(byte b[], int off, int len) throws IOException 和
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
下面看它的子类FileInputStream的实现,
/* File Descriptor - handle to the open file */
private FileDescriptor fd;
这个很重要,这是文件句柄,C语言使用fopen函数的都知道。
/**
* Opens the specified file for reading.
* @param name the name of the file
*/
private native void open(String name) throws FileNotFoundException; /**
* Reads a byte of data from this input stream. This method blocks
* if no input is yet available.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* file is reached.
* @exception IOException if an I/O error occurs.
*/
public native int read() throws IOException;
/**
* Reads a subarray as a sequence of bytes.
* @param b the data to be written
* @param off the start offset in the data
* @param len the number of bytes that are written
* @exception IOException If an I/O error has occurred.
*/
private native int readBytes(byte b[], int off, int len) throws IOException;
子类修改了父的实现
/**
* Reads up to <code>b.length</code> bytes of data from this input
* stream into an array of bytes. This method blocks until some input
* is available.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the file has been reached.
* @exception IOException if an I/O error occurs.
*/
public int read(byte b[]) throws IOException {
return readBytes(b, 0, b.length);
} /**
* Reads up to <code>len</code> bytes of data from this input stream
* into an array of bytes. If <code>len</code> is not zero, the method
* blocks until some input is available; otherwise, no
* bytes are read and <code>0</code> is returned.
*
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array <code>b</code>
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the file has been reached.
* @exception NullPointerException If <code>b</code> is <code>null</code>.
* @exception IndexOutOfBoundsException If <code>off</code> is negative,
* <code>len</code> is negative, or <code>len</code> is greater than
* <code>b.length - off</code>
* @exception IOException if an I/O error occurs.
*/
public int read(byte b[], int off, int len) throws IOException {
return readBytes(b, off, len);
}
看出readBytes是关键的所在,windows的native code中只有 JNIEXPORT void JNICALL
Java_java_io_FileInputStream_close0(JNIEnv *env, jobject this) {
handleClose(env, this, fis_fd);
}
是平台相关的。
其他的在share中
FileInputStream.c代码
jfieldID fis_fd; /* id for jobject 'fd' in java.io.FileInputStream */ /**************************************************************
* static methods to store field ID's in initializers
*/
得到fd的值,这个很重要
JNIEXPORT void JNICALL
Java_java_io_FileInputStream_initIDs(JNIEnv *env, jclass fdClass) {
fis_fd = (*env)->GetFieldID(env, fdClass, "fd", "Ljava/io/FileDescriptor;");
} /**************************************************************
* Input stream
*/ JNIEXPORT void JNICALL
Java_java_io_FileInputStream_open(JNIEnv *env, jobject this, jstring path) {
fileOpen(env, this, path, fis_fd, O_RDONLY);
} JNIEXPORT jint JNICALL
Java_java_io_FileInputStream_read(JNIEnv *env, jobject this) {
return readSingle(env, this, fis_fd);
} JNIEXPORT jint JNICALL
Java_java_io_FileInputStream_readBytes(JNIEnv *env, jobject this,
jbyteArray bytes, jint off, jint len) {
return readBytes(env, this, bytes, off, len, fis_fd);
} JNIEXPORT jlong JNICALL
Java_java_io_FileInputStream_skip(JNIEnv *env, jobject this, jlong toSkip) {
jlong cur = jlong_zero;
jlong end = jlong_zero;
FD fd = GET_FD(this, fis_fd);
if ((cur = IO_Lseek(fd, (jlong)0, (jint)SEEK_CUR)) == -1) {
JNU_ThrowIOExceptionWithLastError(env, "Seek error");
} else if ((end = IO_Lseek(fd, toSkip, (jint)SEEK_CUR)) == -1) {
JNU_ThrowIOExceptionWithLastError(env, "Seek error");
}
return (end - cur);
} JNIEXPORT jint JNICALL
Java_java_io_FileInputStream_available(JNIEnv *env, jobject this) {
jlong ret;
FD fd = GET_FD(this, fis_fd); if (IO_Available(fd, &ret)) {
if (ret > INT_MAX) {
ret = (jlong) INT_MAX;
}
return jlong_to_jint(ret);
}
JNU_ThrowIOExceptionWithLastError(env, NULL);
return 0;
}
主要是readBytes的实现,打开io_util.c文件
/* IO helper functions */ int
readSingle(JNIEnv *env, jobject this, jfieldID fid) {
int nread;
char ret;
FD fd = GET_FD(this, fid); nread = IO_Read(fd, &ret, 1);
if (nread == 0) { /* EOF */
return -1;
} else if (nread == JVM_IO_ERR) { /* error */
JNU_ThrowIOExceptionWithLastError(env, "Read error");
} else if (nread == JVM_IO_INTR) {
JNU_ThrowByName(env, "java/io/InterruptedIOException", 0);
}
return ret & 0xFF;
} /* The maximum size of a stack-allocated buffer.
*/
#define BUF_SIZE 8192
int
readBytes(JNIEnv *env, jobject this, jbyteArray bytes,
jint off, jint len, jfieldID fid)
{
int nread, datalen;
char stackBuf[BUF_SIZE];
char *buf = 0;
FD fd; if (IS_NULL(bytes)) {
JNU_ThrowNullPointerException(env, 0);
return -1;
}
datalen = (*env)->GetArrayLength(env, bytes); if ((off < 0) || (off > datalen) ||
(len < 0) || ((off + len) > datalen) || ((off + len) < 0)) {
JNU_ThrowByName(env, "java/lang/IndexOutOfBoundsException", 0);
return -1;
} if (len == 0) {
return 0;
} else if (len > BUF_SIZE) {
buf = malloc(len);
if (buf == 0) {
JNU_ThrowOutOfMemoryError(env, 0);
return 0;
}
} else {
buf = stackBuf;
} fd = GET_FD(this, fid);
nread = IO_Read(fd, buf, len);
if (nread > 0) {
(*env)->SetByteArrayRegion(env, bytes, off, nread, (jbyte *)buf);
} else if (nread == JVM_IO_ERR) {
JNU_ThrowIOExceptionWithLastError(env, "Read error");
} else if (nread == JVM_IO_INTR) { /* EOF */
JNU_ThrowByName(env, "java/io/InterruptedIOException", 0);
} else { /* EOF */
nread = -1;
} if (buf != stackBuf) {
free(buf);
}
return nread;
}
注意IO_Read在io_util_md.h做了手脚的,
#define IO_Read JVM_Read
其实就是JVM_Read,JVM_Read在hotspot源码中定义的
//%note jvm_r6
return (jint)hpi::read(fd, buf, nbytes);
hpi定义了大量的函数
// HPI_FileInterface
static inline char* native_path(char *path);
static inline int file_type(const char *path);
static inline int open(const char *name, int mode, int perm);
static inline int close(int fd);
static inline jlong lseek(int fd, jlong off, int whence);
static inline int ftruncate(int fd, jlong length);
static inline int fsync(int fd);
static inline int available(int fd, jlong *bytes);
static inline size_t read(int fd, void *buf, unsigned int nBytes);
static inline size_t write(int fd, const void *buf, unsigned int nBytes);
static inline int fsize(int fd, jlong *size);
这就是和平台相关的代码了。window下通过HPIDECL宏转换的 这就是源代码的一小段,根据他的描述,里面都有c的fopen等函数,都是有内存操作的,所以一开始就进入内存了