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59 lines
2.9 KiB
Markdown
59 lines
2.9 KiB
Markdown
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---
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title: File System support
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---
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CheerpJ provides full filesystem support for converted Java applications.
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Read only and read/write filesystems are exposed in Java and can be used to read, write and manipulate files as normally when running on a JVM.
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**Note**: CheerpJ provides access to a virtualized filesystem, which does not correspond to the local computer. Accessing local files from the browser it's forbidden for security reasons.
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# File Systems in CheerpJ
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CheerpJ implements three main filesystem concepts:
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1. A read-only, HTTP-based filesystem
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2. A read/write, IndexedDB-based, persistent filesystem
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3. A read-only, memory based filesystem
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CheerpJ filesystems are implemented as UNIX-style virtual filesystems with multiple mount points. The default mount points are defined as follows:
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1. ```/app/``` → An HTTP-based read-only filesystem, used to access JARs and data from your local server.
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2. ```/files/``` → An IndexedDB-based, persistent read-write file system
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3. ```/lt/``` → Another HTTP-based read-only filesystem, pointing to the CheerpJ runtime
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4. ```/str/``` → A read-only filesystem to easily share JavaScript Strings or binary data (an ```Uint8Array```) with Java code
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# ```/app/``` mount point
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The /app/ mount point corresponds to a virtual read-only, HTTP-based filesystem. ```/app/``` is used to access JAR files and data from your local server.
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The ```/app/``` directory is virtual, and only exists inside of CheerpJ. It is required to distinguish files from the local server from runtime files and files stored in the browser database.
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The ```/app/``` directory refers to the root of your web server. So, assuming that your web server is available at ```http://127.0.0.1:8080/```, here are some example file mappings:
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* ```/app/example.jar``` → ```http://127.0.0.1:8080/example.jar```
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* ```/app/subdirectory/example.txt``` → ```http://127.0.0.1:8080/subdirectory/example.txt```
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# ```/files/``` mount point
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The ```/files/``` mount point corresponds to a virtual read-write, IndexedDB-based filesystem. ```/files/``` is used to store persistent data on the browser client.
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The ```/files/``` directory is a virtual concept used by CheerpJ to store and refer to files.
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# ```/str/``` mount point
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The ```/str/``` mount point is a simple read-only filesystem that can be populated from JavaScript to share data with Java code.
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From JavaScript you can add files into the filesystem using the ```cheerpjAddStringFile``` API. Example:
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```
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cheerpjAddStringFile("/str/fileName.txt", "Some text in a JS String");
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```
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You can access this data from Java, for example:
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```
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import java.io.FileReader;
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...
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FileReader f = new FileReader("/str/fileName.txt")
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...
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```
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The ```cheerpjAddStringFile``` API can be used with JavaScript ```String```s or ```Uint8Array```s. ```Uint8Array```s may be useful to provide binary data to the Java application, for example a user selected file coming from an HTML5 ```<input type="file">``` tag.
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