GeoTools学习笔记-----ShapeFile文件说明----读取DBF文件——DbaseFileReader类的说明

本文介绍了一个用于读取dBase III格式文件的Java类DbaseFileReader。该类提供了读取文件头、记录和字段的方法，并展示了如何使用这些方法来处理DBF文件中的数据。

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/* * GeoTools - The Open Source Java GIS Toolkit * http://geotools.org * * (C) 2002-2008, Open Source Geospatial Foundation (OSGeo) * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; * version 2.1 of the License. * * This library 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 * Lesser General Public License for more details. * * This file is based on an origional contained in the GISToolkit project: * http://gistoolkit.sourceforge.net/ * * * ------------------- * 程序说明文件 * 张恒才 */ package org.geotools.data.shapefile.dbf; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.CharBuffer; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; import java.nio.channels.ReadableByteChannel; import java.nio.charset.Charset; import java.nio.charset.CharsetDecoder; import java.util.Calendar; import org.geotools.data.shapefile.FileReader; import org.geotools.data.shapefile.ShpFileType; import org.geotools.data.shapefile.ShpFiles; import org.geotools.data.shapefile.StreamLogging; import org.geotools.resources.NIOUtilities; /** * A DbaseFileReader is used to read a dbase III format file. <br> * The general use of this class is: <CODE><PRE> * * FileChannel in = new FileInputStream("thefile.dbf").getChannel(); * DbaseFileReader r = new DbaseFileReader( in ) Object[] fields = new * Object[r.getHeader().getNumFields()]; while (r.hasNext()) { * r.readEntry(fields); // do stuff } r.close(); * * </PRE></CODE> For consumers who wish to be a bit more selective with their reading * of rows, the Row object has been added. The semantics are the same as using * the readEntry method, but remember that the Row object is always the same. * The values are parsed as they are read, so it pays to copy them out (as each * call to Row.read() will result in an expensive String parse). <br> * <b>EACH CALL TO readEntry OR readRow ADVANCES THE FILE!</b><br> * An example of using the Row method of reading: <CODE><PRE> * * FileChannel in = new FileInputStream("thefile.dbf").getChannel(); * DbaseFileReader r = new DbaseFileReader( in ) int fields = * r.getHeader().getNumFields(); while (r.hasNext()) { DbaseFileReader.Row row = * r.readRow(); for (int i = 0; i < fields; i++) { // do stuff Foo.bar( * row.read(i) ); } } r.close(); * * </PRE></CODE> * * @author Ian Schneider * @source $URL: * http://svn.geotools.org/geotools/trunk/gt/modules/plugin/shapefile/src/main/java/org/geotools/data/shapefile/dbf/DbaseFileReader.java $ * ----------------------- *该文件说明了怎样的给出一个读取和写dbf文件并给出了一些例子说明 *功能主要目的： *（１）返回dbf文件头 *（2）返回一行记录 *（3）返回一行记录中某个字段值 */ public class DbaseFileReader implements FileReader { // 需要明确行的概念 public final class Row { // 返回某一列的值也就是某一行所对应的字段 public Object read(int column) throws IOException { int offset = getOffset(column); return readObject(offset, column); } // 给出行的描述 // 输出结果： // DBF ROW--FieldName: 个数 public String toString() { StringBuffer ret = new StringBuffer("DBF Row - "); for (int i = 0; i < header.getNumFields(); i++) { ret.append(header.getFieldName(i)).append(": /""); try { ret.append(this.read(i)); } catch (IOException ioe) { ret.append(ioe.getMessage()); } ret.append("/" "); } return ret.toString(); } } // ------------------------------------------------------- // 读取dbf是需要赋值 // 比较重要的变量 // 文件头 DbaseFileHeader header; ByteBuffer buffer; ReadableByteChannel channel; CharBuffer charBuffer; Charset charset; CharsetDecoder decoder; char[] fieldTypes; int[] fieldLengths; int cnt = 1; Row row; // -------------------------------------------------------------------- protected boolean useMemoryMappedBuffer; protected boolean randomAccessEnabled; protected int currentOffset = 0; private StreamLogging streamLogger = new StreamLogging("Dbase File Reader"); private Charset stringCharset; /** * Creates a new instance of DBaseFileReader * * @param shapefileFiles. * The readable channel to use. * @throws IOException * If an error occurs while initializing. * * ------ 读取函数 */ public DbaseFileReader(ShpFiles shapefileFiles, boolean useMemoryMappedBuffer, Charset charset) throws IOException { ReadableByteChannel dbfChannel = shapefileFiles.getReadChannel( ShpFileType.DBF, this); init(dbfChannel, useMemoryMappedBuffer, charset); } // 函数重载 public DbaseFileReader(ReadableByteChannel readChannel, boolean useMemoryMappedBuffer, Charset charset) throws IOException { init(readChannel, useMemoryMappedBuffer, charset); } // 重要的函数 // 实际的读取函数 private void init(ReadableByteChannel dbfChannel, boolean useMemoryMappedBuffer, Charset charset) throws IOException { this.channel = dbfChannel; this.stringCharset = charset; this.charset = Charset.forName("ISO-8859-1"); // charset; this.useMemoryMappedBuffer = useMemoryMappedBuffer; this.randomAccessEnabled = (channel instanceof FileChannel); streamLogger.open(); header = new DbaseFileHeader(); // 读取文件头 header.readHeader(channel); // create the ByteBuffer // if we have a FileChannel, lets map it if (channel instanceof FileChannel && this.useMemoryMappedBuffer) { FileChannel fc = (FileChannel) channel; buffer = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size()); buffer.position((int) fc.position()); this.currentOffset = 0; } else { // Force useMemoryMappedBuffer to false this.useMemoryMappedBuffer = false; // Some other type of channel // start with a 8K buffer, should be more than adequate int size = 8 * 1024; // if for some reason its not, resize it size = header.getRecordLength() > size ? header.getRecordLength() : size; buffer = ByteBuffer.allocateDirect(size); // fill it and reset fill(buffer, channel); buffer.flip(); this.currentOffset = header.getHeaderLength(); } // The entire file is in little endian buffer.order(ByteOrder.LITTLE_ENDIAN); // Set up some buffers and lookups for efficiency fieldTypes = new char[header.getNumFields()]; fieldLengths = new int[header.getNumFields()]; for (int i = 0, ii = header.getNumFields(); i < ii; i++) { fieldTypes[i] = header.getFieldType(i); fieldLengths[i] = header.getFieldLength(i); } charBuffer = CharBuffer.allocate(header.getRecordLength() - 1); decoder = charset.newDecoder(); row = new Row(); } protected int fill(ByteBuffer buffer, ReadableByteChannel channel) throws IOException { int r = buffer.remaining(); // channel reads return -1 when EOF or other error // because they a non-blocking reads, 0 is a valid return value!! while (buffer.remaining() > 0 && r != -1) { r = channel.read(buffer); } if (r == -1) { buffer.limit(buffer.position()); } return r; } private void bufferCheck() throws IOException { // remaining is less than record length // compact the remaining data and read again if (!buffer.isReadOnly() && buffer.remaining() < header.getRecordLength()) { // if (!this.useMemoryMappedBuffer) { this.currentOffset += buffer.position(); // } buffer.compact(); fill(buffer, channel); buffer.position(0); } } private int getOffset(int column) { int offset = 0; for (int i = 0, ii = column; i < ii; i++) { offset += fieldLengths[i]; } return offset; } /** * Get the header from this file. The header is read upon instantiation. * * @return The header associated with this file or null if an error * occurred. * * 返回文件头的说明 */ public DbaseFileHeader getHeader() { return header; } /** * Clean up all resources associated with this reader.<B>Highly recomended.</B> * * @throws IOException * If an error occurs. 关闭读写 */ public void close() throws IOException { if (channel.isOpen()) { channel.close(); streamLogger.close(); } if (buffer instanceof MappedByteBuffer) { NIOUtilities.clean(buffer); } buffer = null; channel = null; charBuffer = null; decoder = null; header = null; row = null; } /** * Query the reader as to whether there is another record. * * @return True if more records exist, false otherwise. * * 根据文件头中记录个数进行查找 */ public boolean hasNext() { return cnt < header.getNumRecords() + 1; } /** * Get the next record (entry). Will return a new array of values. * * @throws IOException * If an error occurs. * @return A new array of values. */ public Object[] readEntry() throws IOException { // /读取一条记录 return readEntry(new Object[header.getNumFields()]); } public Row readRow() throws IOException { read(); return row; } /** * Skip the next record. * * @throws IOException * If an error occurs. 跳过一条记录 */ public void skip() throws IOException { boolean foundRecord = false; while (!foundRecord) { bufferCheck(); // read the deleted flag char tempDeleted = (char) buffer.get(); // skip the next bytes buffer.position(buffer.position() + header.getRecordLength() - 1); // the // 1 is // for // the // deleted // flag // just // read. // add the row if it is not deleted. if (tempDeleted != '*') { foundRecord = true; } } } /** * Copy the next record into the array starting at offset. * * @param entry * Th array to copy into. * @param offset * The offset to start at * @throws IOException * If an error occurs. * @return The same array passed in. 复制一条记录到一个数组 */ public Object[] readEntry(Object[] entry, final int offset) throws IOException { if (entry.length - offset < header.getNumFields()) { throw new ArrayIndexOutOfBoundsException(); } read(); // retrieve the record length final int numFields = header.getNumFields(); int fieldOffset = 0; for (int j = 0; j < numFields; j++) { entry[j + offset] = readObject(fieldOffset, j); fieldOffset += fieldLengths[j]; } return entry; } /** * Reads a single field from the current record and returns it. Remember to * call {@link #read()} before starting to read fields from the dbf, and * call it every time you need to move to the next record. * * @param fieldNum * The field number to be read (zero based) * @throws IOException * If an error occurs. * @return The value of the field ----- 返回当前记录的中某个字段所对应的值实际调用的是ReadObject的 */ public Object readField(int fieldNum) throws IOException { // retrieve the record length int fieldOffset = 0; for (int j = 0; j < fieldNum; j++) { fieldOffset += fieldLengths[j]; } return readObject(fieldOffset, fieldNum); } /** * Transfer, by bytes, the next record to the writer. */ public void transferTo(DbaseFileWriter writer) throws IOException { bufferCheck(); buffer.limit(buffer.position() + header.getRecordLength()); writer.channel.write(buffer); buffer.limit(buffer.capacity()); cnt++; } /** * Reads the next record into memory. You need to use this directly when * reading only a subset of the fields using {@link #readField(int)}. * * @throws IOException */ public void read() throws IOException { boolean foundRecord = false; while (!foundRecord) { bufferCheck(); // read the deleted flag char deleted = (char) buffer.get(); if (deleted == '*') { continue; } charBuffer.position(0); buffer.limit(buffer.position() + header.getRecordLength() - 1); decoder.decode(buffer, charBuffer, true); buffer.limit(buffer.capacity()); charBuffer.flip(); foundRecord = true; } cnt++; } /** * Copy the next entry into the array. * * @param entry * The array to copy into. * @throws IOException * If an error occurs. * @return The same array passed in. */ public Object[] readEntry(Object[] entry) throws IOException { return readEntry(entry, 0); } private Object readObject(final int fieldOffset, final int fieldNum) throws IOException { final char type = fieldTypes[fieldNum]; final int fieldLen = fieldLengths[fieldNum]; Object object = null; // System.out.println( charBuffer.subSequence(fieldOffset,fieldOffset + // fieldLen)); if (fieldLen > 0) { switch (type) { // (L)logical (T,t,F,f,Y,y,N,n) case 'l': case 'L': switch (charBuffer.charAt(fieldOffset)) { case 't': case 'T': case 'Y': case 'y': object = Boolean.TRUE; break; case 'f': case 'F': case 'N': case 'n': object = Boolean.FALSE; break; default: throw new IOException("Unknown logical value : '" + charBuffer.charAt(fieldOffset) + "'"); } break; // (C)character (String) case 'c': case 'C': // oh, this seems like a lot of work to parse strings...but, // For some reason if zero characters ( (int) char == 0 ) are // allowed // in these strings, they do not compare correctly later on down // the // line.... int start = fieldOffset; int end = fieldOffset + fieldLen - 1; charBuffer.limit(charBuffer.capacity()); // trim off whitespace and 'zero' chars while (start < end) { char c = charBuffer.get(start); if (c == 0 || Character.isWhitespace(c)) { start++; } else break; } while (end > start) { char c = charBuffer.get(end); if (c == 0 || Character.isWhitespace(c)) { end--; } else break; } // set up the new indexes for start and end charBuffer.position(start).limit(end + 1); String s = charBuffer.toString(); charBuffer.clear(); object = s; break; // (D)date (Date) case 'd': case 'D': try { String tempString = charBuffer.subSequence(fieldOffset, fieldOffset + 4).toString(); int tempYear = Integer.parseInt(tempString); tempString = charBuffer.subSequence(fieldOffset + 4, fieldOffset + 6).toString(); int tempMonth = Integer.parseInt(tempString) - 1; tempString = charBuffer.subSequence(fieldOffset + 6, fieldOffset + 8).toString(); int tempDay = Integer.parseInt(tempString); Calendar cal = Calendar.getInstance(); cal.clear(); cal.set(Calendar.YEAR, tempYear); cal.set(Calendar.MONTH, tempMonth); cal.set(Calendar.DAY_OF_MONTH, tempDay); object = cal.getTime(); } catch (NumberFormatException nfe) { // todo: use progresslistener, this isn't a grave error. } break; // (F)floating (Double) case 'n': case 'N': try { final Class clazz = header.getFieldClass(fieldNum); final String number = extractNumberString(charBuffer, fieldOffset, fieldLen); if (clazz == Integer.class) { object = new Integer(number); break; } else if (clazz == Long.class) { object = new Long(number); break; } // else will fall through to the floating point number } catch (NumberFormatException e) { // todo: use progresslistener, this isn't a grave error. // don't do this!!! the Double parse will be attemted as we // fall // through, so no need to create a new Object. -IanS // object = new Integer(0); // Lets try parsing a long instead... try { object = new Long(extractNumberString(charBuffer, fieldOffset, fieldLen)); break; } catch (NumberFormatException e2) { } } case 'f': case 'F': // floating point number try { object = new Double(extractNumberString(charBuffer, fieldOffset, fieldLen)); } catch (NumberFormatException e) { // todo: use progresslistener, this isn't a grave error, // though it // does indicate something is wrong // okay, now whatever we got was truly undigestable. Lets go // with // a zero Double. object = new Double(0.0); } break; default: throw new IOException("Invalid field type : " + type); } } return object; } /** * @param charBuffer2 * TODO * @param fieldOffset * @param fieldLen */ private final String extractNumberString(final CharBuffer charBuffer2, final int fieldOffset, final int fieldLen) { String thing = charBuffer2.subSequence(fieldOffset, fieldOffset + fieldLen).toString().trim(); return thing; } // 文件测试代码 /** * 传递参数SHP文件名字 */ public static void main(String[] args) throws Exception { // 新建一个类 DbaseFileReader reader = new DbaseFileReader(new ShpFiles(args[0]), false, Charset.forName("ISO-8859-1")); // 输出文件头 System.out.println(reader.getHeader()); int r = 0; // 迭代读取记录 while (reader.hasNext()) { System.out.println(++r + "," + java.util.Arrays.asList(reader.readEntry())); } // 关闭 reader.close(); } /**=================================== * public void zhc_testRow() { FileChannel in = new FileInputStream("thefile.dbf").getChannel(); DbaseFileReader r = new DbaseFileReader(in); int fields = r.getHeader().getNumFields(); while (r.hasNext()) { //-------一条记录存储在ROW中----------------------------------------------- DbaseFileReader.Row row = r.readRow();//读取一行实际调用Read() for (int i = 0; i < fields; i++) { row.read(i);//某个字段的值--实际调用readObject } //-------------------------------------------------- } r.close(); } public void zhc_testReadEntry() { FileChannel in = new FileInputStream("thefile.dbf").getChannel(); DbaseFileReader r = new DbaseFileReader( in ) ; Object[] fields = new Object[r.getHeader().getNumFields()]; while (r.hasNext()) {//判断是够存在记录 //----------一条记录存储在Fields数组中------------------------------------------------ r.readEntry(fields);//实际调用----Read() //------------------------------------------------------------- } } * */ public String id() { return getClass().getName(); } }