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25 
26 package java.util.jar;
27 
28 import java.util.zip.*;
29 import java.io.*;
30 
31 /**
32  * The <code>JarOutputStream</code> class is used to write the contents
33  * of a JAR file to any output stream. It extends the class
34  * <code>java.util.zip.ZipOutputStream</code> with support
35  * for writing an optional <code>Manifest</code> entry. The
36  * <code>Manifest</code> can be used to specify meta-information about
37  * the JAR file and its entries.
38  *
39  * @author  David Connelly
40  * @see     Manifest
41  * @see     java.util.zip.ZipOutputStream
42  * @since   1.2
43  */
44 public
45 class JarOutputStream extends ZipOutputStream {
46     private static final int JAR_MAGIC = 0xCAFE;
47 
48     /**
49      * Creates a new <code>JarOutputStream</code> with the specified
50      * <code>Manifest</code>. The manifest is written as the first
51      * entry to the output stream.
52      *
53      * @param out the actual output stream
54      * @param man the optional <code>Manifest</code>
55      * @exception IOException if an I/O error has occurred
56      */
JarOutputStream(OutputStream out, Manifest man)57     public JarOutputStream(OutputStream out, Manifest man) throws IOException {
58         super(out);
59         if (man == null) {
60             throw new NullPointerException("man");
61         }
62         ZipEntry e = new ZipEntry(JarFile.MANIFEST_NAME);
63         putNextEntry(e);
64         man.write(new BufferedOutputStream(this));
65         closeEntry();
66     }
67 
68     /**
69      * Creates a new <code>JarOutputStream</code> with no manifest.
70      * @param out the actual output stream
71      * @exception IOException if an I/O error has occurred
72      */
JarOutputStream(OutputStream out)73     public JarOutputStream(OutputStream out) throws IOException {
74         super(out);
75     }
76 
77     /**
78      * Begins writing a new JAR file entry and positions the stream
79      * to the start of the entry data. This method will also close
80      * any previous entry. The default compression method will be
81      * used if no compression method was specified for the entry.
82      * The current time will be used if the entry has no set modification
83      * time.
84      *
85      * @param ze the ZIP/JAR entry to be written
86      * @exception ZipException if a ZIP error has occurred
87      * @exception IOException if an I/O error has occurred
88      */
putNextEntry(ZipEntry ze)89     public void putNextEntry(ZipEntry ze) throws IOException {
90         if (firstEntry) {
91             // Make sure that extra field data for first JAR
92             // entry includes JAR magic number id.
93             byte[] edata = ze.getExtra();
94             if (edata == null || !hasMagic(edata)) {
95                 if (edata == null) {
96                     edata = new byte[4];
97                 } else {
98                     // Prepend magic to existing extra data
99                     byte[] tmp = new byte[edata.length + 4];
100                     System.arraycopy(edata, 0, tmp, 4, edata.length);
101                     edata = tmp;
102                 }
103                 set16(edata, 0, JAR_MAGIC); // extra field id
104                 set16(edata, 2, 0);         // extra field size
105                 ze.setExtra(edata);
106             }
107             firstEntry = false;
108         }
109         super.putNextEntry(ze);
110     }
111 
112     private boolean firstEntry = true;
113 
114     /*
115      * Returns true if specified byte array contains the
116      * jar magic extra field id.
117      */
hasMagic(byte[] edata)118     private static boolean hasMagic(byte[] edata) {
119         try {
120             int i = 0;
121             while (i < edata.length) {
122                 if (get16(edata, i) == JAR_MAGIC) {
123                     return true;
124                 }
125                 i += get16(edata, i + 2) + 4;
126             }
127         } catch (ArrayIndexOutOfBoundsException e) {
128             // Invalid extra field data
129         }
130         return false;
131     }
132 
133     /*
134      * Fetches unsigned 16-bit value from byte array at specified offset.
135      * The bytes are assumed to be in Intel (little-endian) byte order.
136      */
get16(byte[] b, int off)137     private static int get16(byte[] b, int off) {
138         return Byte.toUnsignedInt(b[off]) | ( Byte.toUnsignedInt(b[off+1]) << 8);
139     }
140 
141     /*
142      * Sets 16-bit value at specified offset. The bytes are assumed to
143      * be in Intel (little-endian) byte order.
144      */
set16(byte[] b, int off, int value)145     private static void set16(byte[] b, int off, int value) {
146         b[off+0] = (byte)value;
147         b[off+1] = (byte)(value >> 8);
148     }
149 }
150