| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.iapi.services.io.LimitReader |
| 4 | |
| 5 | Copyright 1999, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.iapi.services.io; |
| 22 | |
| 23 | import java.io.Reader; |
| 24 | import java.io.IOException; |
| 25 | |
| 26 | /** |
| 27 | A Reader that provides methods to limit the range that |
| 28 | can be read from the reader. |
| 29 | */ |
| 30 | public final class LimitReader extends Reader implements Limit |
| 31 | { |
| 32 | private int remainingCharacters; |
| 33 | private boolean limitInPlace; |
| 34 | private Reader reader; |
| 35 | |
| 36 | /** |
| 37 | Construct a LimitReader and call the clearLimit() method. |
| 38 | */ |
| 39 | public LimitReader(Reader reader) |
| 40 | { |
| 41 | super(); |
| 42 | this.reader = reader; |
| 43 | clearLimit(); |
| 44 | } |
| 45 | |
| 46 | public int read() throws IOException |
| 47 | { |
| 48 | |
| 49 | if (!limitInPlace) |
| 50 | return reader.read(); |
| 51 | |
| 52 | if (remainingCharacters == 0) |
| 53 | return -1; // end of file |
| 54 | |
| 55 | |
| 56 | int value = reader.read(); |
| 57 | if (value >= 0) |
| 58 | remainingCharacters--; |
| 59 | return value; |
| 60 | |
| 61 | } |
| 62 | |
| 63 | public int read(char c[], int off, int len) throws IOException |
| 64 | { |
| 65 | if (!limitInPlace) |
| 66 | return reader.read(c, off, len); |
| 67 | |
| 68 | if (remainingCharacters == 0) |
| 69 | return -1; |
| 70 | |
| 71 | if (remainingCharacters < len) |
| 72 | { |
| 73 | len = remainingCharacters; // end of file |
| 74 | } |
| 75 | |
| 76 | len = reader.read(c, off, len); |
| 77 | if (len >= 0) |
| 78 | remainingCharacters -= len; |
| 79 | return len; |
| 80 | } |
| 81 | |
| 82 | public long skip(long count) |
| 83 | throws IOException |
| 84 | { |
| 85 | if (!limitInPlace) |
| 86 | return reader.skip(count); |
| 87 | |
| 88 | if (remainingCharacters == 0) |
| 89 | return 0; // end of file |
| 90 | |
| 91 | if (remainingCharacters < count) |
| 92 | count = remainingCharacters; |
| 93 | |
| 94 | count = reader.skip(count); |
| 95 | remainingCharacters -= count; |
| 96 | return count; |
| 97 | } |
| 98 | |
| 99 | public void close() |
| 100 | throws IOException |
| 101 | { |
| 102 | reader.close(); |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | Set the limit of the stream that can be read. After this |
| 107 | call up to and including length characters can be read from |
| 108 | or skipped in the stream. |
| 109 | Any attempt to read more than length characters will |
| 110 | result in an EOFException |
| 111 | |
| 112 | @exception IOException IOException from some underlying stream |
| 113 | @exception EOFException The set limit would exceed |
| 114 | the available data in the stream. |
| 115 | */ |
| 116 | public void setLimit(int length) |
| 117 | { |
| 118 | remainingCharacters = length; |
| 119 | limitInPlace = true; |
| 120 | return; |
| 121 | } |
| 122 | |
| 123 | /** |
| 124 | * return limit of the stream that can be read without throwing |
| 125 | * EOFException |
| 126 | * @return the remaining characters left to be read from the stream |
| 127 | */ |
| 128 | public final int getLimit() |
| 129 | { |
| 130 | return remainingCharacters; |
| 131 | } |
| 132 | |
| 133 | /** |
| 134 | Clear any limit set by setLimit. After this call no limit checking |
| 135 | will be made on any read until a setLimit()) call is made. |
| 136 | |
| 137 | @return the number of bytes within the limit that have not been read. |
| 138 | -1 if not limit was set. |
| 139 | */ |
| 140 | public int clearLimit() |
| 141 | { |
| 142 | int leftOver = remainingCharacters; |
| 143 | limitInPlace = false; |
| 144 | remainingCharacters = -1; |
| 145 | return leftOver; |
| 146 | } |
| 147 | } |