1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
grpc Examples
==============================================
The examples require grpc-java to already be built. You are strongly encouraged
to check out a git release tag, since there will already be a build of grpc
available. Otherwise you must follow [COMPILING](../COMPILING.md).
You may want to read through the
[Quick Start Guide](https://grpc.io/docs/quickstart/java.html)
before trying out the examples.
## Basic examples
- [Hello world](src/main/java/io/grpc/examples/helloworld)
- [Route guide](src/main/java/io/grpc/examples/routeguide)
- [Metadata](src/main/java/io/grpc/examples/header)
- [Error handling](src/main/java/io/grpc/examples/errorhandling)
- [Compression](src/main/java/io/grpc/examples/experimental)
- [Flow control](src/main/java/io/grpc/examples/manualflowcontrol)
- [Json serialization](src/main/java/io/grpc/examples/advanced)
- <details>
<summary>Hedging</summary>
The [hedging example](src/main/java/io/grpc/examples/hedging) demonstrates that enabling hedging
can reduce tail latency. (Users should note that enabling hedging may introduce other overhead;
and in some scenarios, such as when some server resource gets exhausted for a period of time and
almost every RPC during that time has high latency or fails, hedging may make things worse.
Setting a throttle in the service config is recommended to protect the server from too many
inappropriate retry or hedging requests.)
The server and the client in the example are basically the same as those in the
[hello world](src/main/java/io/grpc/examples/helloworld) example, except that the server mimics a
long tail of latency, and the client sends 2000 requests and can turn on and off hedging.
To mimic the latency, the server randomly delays the RPC handling by 2 seconds at 10% chance, 5
seconds at 5% chance, and 10 seconds at 1% chance.
When running the client enabling the following hedging policy
```json
"hedgingPolicy": {
"maxAttempts": 3,
"hedgingDelay": "1s"
}
```
Then the latency summary in the client log is like the following
```text
Total RPCs sent: 2,000. Total RPCs failed: 0
[Hedging enabled]
========================
50% latency: 0ms
90% latency: 6ms
95% latency: 1,003ms
99% latency: 2,002ms
99.9% latency: 2,011ms
Max latency: 5,272ms
========================
```
See [the section below](#to-build-the-examples) for how to build and run the example. The
executables for the server and the client are `hedging-hello-world-server` and
`hedging-hello-world-client`.
To disable hedging, set environment variable `DISABLE_HEDGING_IN_HEDGING_EXAMPLE=true` before
running the client. That produces a latency summary in the client log like the following
```text
Total RPCs sent: 2,000. Total RPCs failed: 0
[Hedging disabled]
========================
50% latency: 0ms
90% latency: 2,002ms
95% latency: 5,002ms
99% latency: 10,004ms
99.9% latency: 10,007ms
Max latency: 10,007ms
========================
```
</details>
### <a name="to-build-the-examples"></a> To build the examples
1. **[Install gRPC Java library SNAPSHOT locally, including code generation plugin](../COMPILING.md) (Only need this step for non-released versions, e.g. master HEAD).**
2. From grpc-java/examples directory:
```
$ ./gradlew installDist
```
This creates the scripts `hello-world-server`, `hello-world-client`,
`route-guide-server`, `route-guide-client`, etc. in the
`build/install/examples/bin/` directory that run the examples. Each
example requires the server to be running before starting the client.
For example, to try the hello world example first run:
```
$ ./build/install/examples/bin/hello-world-server
```
And in a different terminal window run:
```
$ ./build/install/examples/bin/hello-world-client
```
That's it!
Please refer to gRPC Java's [README](../README.md) and
[tutorial](https://grpc.io/docs/tutorials/basic/java.html) for more
information.
### Maven
If you prefer to use Maven:
1. **[Install gRPC Java library SNAPSHOT locally, including code generation plugin](../COMPILING.md) (Only need this step for non-released versions, e.g. master HEAD).**
2. Run in this directory:
```
$ mvn verify
$ # Run the server
$ mvn exec:java -Dexec.mainClass=io.grpc.examples.helloworld.HelloWorldServer
$ # In another terminal run the client
$ mvn exec:java -Dexec.mainClass=io.grpc.examples.helloworld.HelloWorldClient
```
### Bazel
If you prefer to use Bazel:
```
$ bazel build :hello-world-server :hello-world-client
$ # Run the server
$ bazel-bin/hello-world-server
$ # In another terminal run the client
$ bazel-bin/hello-world-client
```
## Other examples
- [Android examples](android)
- Secure channel examples
+ [TLS examples](example-tls)
+ [ALTS examples](example-alts)
- [Google Authentication](example-gauth)
- [Kotlin examples](example-kotlin)
- [Kotlin Android examples](example-kotlin/android)
## Unit test examples
Examples for unit testing gRPC clients and servers are located in [examples/src/test](src/test).
In general, we DO NOT allow overriding the client stub and we DO NOT support mocking final methods
in gRPC-Java library. Users should be cautious that using tools like PowerMock or
[mockito-inline](https://search.maven.org/search?q=g:org.mockito%20a:mockito-inline) can easily
break this rule of thumb. We encourage users to leverage `InProcessTransport` as demonstrated in the
examples to write unit tests. `InProcessTransport` is light-weight and runs the server
and client in the same process without any socket/TCP connection.
Mocking the client stub provides a false sense of security when writing tests. Mocking stubs and responses
allows for tests that don't map to reality, causing the tests to pass, but the system-under-test to fail.
The gRPC client library is complicated, and accurately reproducing that complexity with mocks is very hard.
You will be better off and write less code by using `InProcessTransport` instead.
Example bugs not caught by mocked stub tests include:
* Calling the stub with a `null` message
* Not calling `close()`
* Sending invalid headers
* Ignoring deadlines
* Ignoring cancellation
For testing a gRPC client, create the client with a real stub
using an
[InProcessChannel](../core/src/main/java/io/grpc/inprocess/InProcessChannelBuilder.java),
and test it against an
[InProcessServer](../core/src/main/java/io/grpc/inprocess/InProcessServerBuilder.java)
with a mock/fake service implementation.
For testing a gRPC server, create the server as an InProcessServer,
and test it against a real client stub with an InProcessChannel.
The gRPC-java library also provides a JUnit rule,
[GrpcCleanupRule](../testing/src/main/java/io/grpc/testing/GrpcCleanupRule.java), to do the graceful
shutdown boilerplate for you.
## Even more examples
A wide variety of third-party examples can be found [here](https://github.com/saturnism/grpc-java-by-example).
|
