Modifying a text file in a ZIP archive in Java

Java 7 introduced a much simpler way for doing zip archive manipulations – FileSystems API, which allows to access contents of a file as a file system.

Besides much more straightforward API, it is doing the modification in-place and doesn’t require to rewrite other (irrelevant) files in a zip archive (as done in the accepted answer).

Here’s sample code that solves OP’s use case:

import java.io.*;
import java.nio.file.*;

public static void main(String[] args) throws IOException {
    modifyTextFileInZip("test.zip");
}

static void modifyTextFileInZip(String zipPath) throws IOException {
    Path zipFilePath = Paths.get(zipPath);
    try (FileSystem fs = FileSystems.newFileSystem(zipFilePath, null)) {
        Path source = fs.getPath("/abc.txt");
        Path temp = fs.getPath("/___abc___.txt");
        if (Files.exists(temp)) {
            throw new IOException("temp file exists, generate another name");
        }
        Files.move(source, temp);
        streamCopy(temp, source);
        Files.delete(temp);
    }
}

static void streamCopy(Path src, Path dst) throws IOException {
    try (BufferedReader br = new BufferedReader(
            new InputStreamReader(Files.newInputStream(src)));
         BufferedWriter bw = new BufferedWriter(
            new OutputStreamWriter(Files.newOutputStream(dst)))) {

        String line;
        while ((line = br.readLine()) != null) {
            line = line.replace("key1=value1", "key1=value2");
            bw.write(line);
            bw.newLine();
        }
    }
}

For more zip archive manipulation examples, see demo/nio/zipfs/Demo.java sample which you can download here (look for JDK 8 Demos and Samples).